1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  *  linux/fs/buffer.c
4  *
5  *  Copyright (C) 1991, 1992, 2002  Linus Torvalds
6  */
7 
8 /*
9  * Start bdflush() with kernel_thread not syscall - Paul Gortmaker, 12/95
10  *
11  * Removed a lot of unnecessary code and simplified things now that
12  * the buffer cache isn't our primary cache - Andrew Tridgell 12/96
13  *
14  * Speed up hash, lru, and free list operations.  Use gfp() for allocating
15  * hash table, use SLAB cache for buffer heads. SMP threading.  -DaveM
16  *
17  * Added 32k buffer block sizes - these are required older ARM systems. - RMK
18  *
19  * async buffer flushing, 1999 Andrea Arcangeli <andrea@suse.de>
20  */
21 
22 #include <linux/kernel.h>
23 #include <linux/sched/signal.h>
24 #include <linux/syscalls.h>
25 #include <linux/fs.h>
26 #include <linux/iomap.h>
27 #include <linux/mm.h>
28 #include <linux/percpu.h>
29 #include <linux/slab.h>
30 #include <linux/capability.h>
31 #include <linux/blkdev.h>
32 #include <linux/file.h>
33 #include <linux/quotaops.h>
34 #include <linux/highmem.h>
35 #include <linux/export.h>
36 #include <linux/backing-dev.h>
37 #include <linux/writeback.h>
38 #include <linux/hash.h>
39 #include <linux/suspend.h>
40 #include <linux/buffer_head.h>
41 #include <linux/task_io_accounting_ops.h>
42 #include <linux/bio.h>
43 #include <linux/cpu.h>
44 #include <linux/bitops.h>
45 #include <linux/mpage.h>
46 #include <linux/bit_spinlock.h>
47 #include <linux/pagevec.h>
48 #include <linux/sched/mm.h>
49 #include <trace/events/block.h>
50 #include <linux/fscrypt.h>
51 
52 #include "internal.h"
53 
54 static int fsync_buffers_list(spinlock_t *lock, struct list_head *list);
55 static int submit_bh_wbc(int op, int op_flags, struct buffer_head *bh,
56 			 struct writeback_control *wbc);
57 
58 #define BH_ENTRY(list) list_entry((list), struct buffer_head, b_assoc_buffers)
59 
touch_buffer(struct buffer_head * bh)60 inline void touch_buffer(struct buffer_head *bh)
61 {
62 	trace_block_touch_buffer(bh);
63 	mark_page_accessed(bh->b_page);
64 }
65 EXPORT_SYMBOL(touch_buffer);
66 
__lock_buffer(struct buffer_head * bh)67 void __lock_buffer(struct buffer_head *bh)
68 {
69 	wait_on_bit_lock_io(&bh->b_state, BH_Lock, TASK_UNINTERRUPTIBLE);
70 }
71 EXPORT_SYMBOL(__lock_buffer);
72 
unlock_buffer(struct buffer_head * bh)73 void unlock_buffer(struct buffer_head *bh)
74 {
75 	clear_bit_unlock(BH_Lock, &bh->b_state);
76 	smp_mb__after_atomic();
77 	wake_up_bit(&bh->b_state, BH_Lock);
78 }
79 EXPORT_SYMBOL(unlock_buffer);
80 
81 /*
82  * Returns if the folio has dirty or writeback buffers. If all the buffers
83  * are unlocked and clean then the folio_test_dirty information is stale. If
84  * any of the buffers are locked, it is assumed they are locked for IO.
85  */
buffer_check_dirty_writeback(struct folio * folio,bool * dirty,bool * writeback)86 void buffer_check_dirty_writeback(struct folio *folio,
87 				     bool *dirty, bool *writeback)
88 {
89 	struct buffer_head *head, *bh;
90 	*dirty = false;
91 	*writeback = false;
92 
93 	BUG_ON(!folio_test_locked(folio));
94 
95 	head = folio_buffers(folio);
96 	if (!head)
97 		return;
98 
99 	if (folio_test_writeback(folio))
100 		*writeback = true;
101 
102 	bh = head;
103 	do {
104 		if (buffer_locked(bh))
105 			*writeback = true;
106 
107 		if (buffer_dirty(bh))
108 			*dirty = true;
109 
110 		bh = bh->b_this_page;
111 	} while (bh != head);
112 }
113 EXPORT_SYMBOL(buffer_check_dirty_writeback);
114 
115 /*
116  * Block until a buffer comes unlocked.  This doesn't stop it
117  * from becoming locked again - you have to lock it yourself
118  * if you want to preserve its state.
119  */
__wait_on_buffer(struct buffer_head * bh)120 void __wait_on_buffer(struct buffer_head * bh)
121 {
122 	wait_on_bit_io(&bh->b_state, BH_Lock, TASK_UNINTERRUPTIBLE);
123 }
124 EXPORT_SYMBOL(__wait_on_buffer);
125 
buffer_io_error(struct buffer_head * bh,char * msg)126 static void buffer_io_error(struct buffer_head *bh, char *msg)
127 {
128 	if (!test_bit(BH_Quiet, &bh->b_state))
129 		printk_ratelimited(KERN_ERR
130 			"Buffer I/O error on dev %pg, logical block %llu%s\n",
131 			bh->b_bdev, (unsigned long long)bh->b_blocknr, msg);
132 }
133 
134 /*
135  * End-of-IO handler helper function which does not touch the bh after
136  * unlocking it.
137  * Note: unlock_buffer() sort-of does touch the bh after unlocking it, but
138  * a race there is benign: unlock_buffer() only use the bh's address for
139  * hashing after unlocking the buffer, so it doesn't actually touch the bh
140  * itself.
141  */
__end_buffer_read_notouch(struct buffer_head * bh,int uptodate)142 static void __end_buffer_read_notouch(struct buffer_head *bh, int uptodate)
143 {
144 	if (uptodate) {
145 		set_buffer_uptodate(bh);
146 	} else {
147 		/* This happens, due to failed read-ahead attempts. */
148 		clear_buffer_uptodate(bh);
149 	}
150 	unlock_buffer(bh);
151 }
152 
153 /*
154  * Default synchronous end-of-IO handler..  Just mark it up-to-date and
155  * unlock the buffer. This is what ll_rw_block uses too.
156  */
end_buffer_read_sync(struct buffer_head * bh,int uptodate)157 void end_buffer_read_sync(struct buffer_head *bh, int uptodate)
158 {
159 	__end_buffer_read_notouch(bh, uptodate);
160 	put_bh(bh);
161 }
162 EXPORT_SYMBOL(end_buffer_read_sync);
163 
end_buffer_write_sync(struct buffer_head * bh,int uptodate)164 void end_buffer_write_sync(struct buffer_head *bh, int uptodate)
165 {
166 	if (uptodate) {
167 		set_buffer_uptodate(bh);
168 	} else {
169 		buffer_io_error(bh, ", lost sync page write");
170 		mark_buffer_write_io_error(bh);
171 		clear_buffer_uptodate(bh);
172 	}
173 	unlock_buffer(bh);
174 	put_bh(bh);
175 }
176 EXPORT_SYMBOL(end_buffer_write_sync);
177 
178 /*
179  * Various filesystems appear to want __find_get_block to be non-blocking.
180  * But it's the page lock which protects the buffers.  To get around this,
181  * we get exclusion from try_to_free_buffers with the blockdev mapping's
182  * private_lock.
183  *
184  * Hack idea: for the blockdev mapping, private_lock contention
185  * may be quite high.  This code could TryLock the page, and if that
186  * succeeds, there is no need to take private_lock.
187  */
188 static struct buffer_head *
__find_get_block_slow(struct block_device * bdev,sector_t block)189 __find_get_block_slow(struct block_device *bdev, sector_t block)
190 {
191 	struct inode *bd_inode = bdev->bd_inode;
192 	struct address_space *bd_mapping = bd_inode->i_mapping;
193 	struct buffer_head *ret = NULL;
194 	pgoff_t index;
195 	struct buffer_head *bh;
196 	struct buffer_head *head;
197 	struct page *page;
198 	int all_mapped = 1;
199 	static DEFINE_RATELIMIT_STATE(last_warned, HZ, 1);
200 
201 	index = block >> (PAGE_SHIFT - bd_inode->i_blkbits);
202 	page = find_get_page_flags(bd_mapping, index, FGP_ACCESSED);
203 	if (!page)
204 		goto out;
205 
206 	spin_lock(&bd_mapping->private_lock);
207 	if (!page_has_buffers(page))
208 		goto out_unlock;
209 	head = page_buffers(page);
210 	bh = head;
211 	do {
212 		if (!buffer_mapped(bh))
213 			all_mapped = 0;
214 		else if (bh->b_blocknr == block) {
215 			ret = bh;
216 			get_bh(bh);
217 			goto out_unlock;
218 		}
219 		bh = bh->b_this_page;
220 	} while (bh != head);
221 
222 	/* we might be here because some of the buffers on this page are
223 	 * not mapped.  This is due to various races between
224 	 * file io on the block device and getblk.  It gets dealt with
225 	 * elsewhere, don't buffer_error if we had some unmapped buffers
226 	 */
227 	ratelimit_set_flags(&last_warned, RATELIMIT_MSG_ON_RELEASE);
228 	if (all_mapped && __ratelimit(&last_warned)) {
229 		printk("__find_get_block_slow() failed. block=%llu, "
230 		       "b_blocknr=%llu, b_state=0x%08lx, b_size=%zu, "
231 		       "device %pg blocksize: %d\n",
232 		       (unsigned long long)block,
233 		       (unsigned long long)bh->b_blocknr,
234 		       bh->b_state, bh->b_size, bdev,
235 		       1 << bd_inode->i_blkbits);
236 	}
237 out_unlock:
238 	spin_unlock(&bd_mapping->private_lock);
239 	put_page(page);
240 out:
241 	return ret;
242 }
243 
end_buffer_async_read(struct buffer_head * bh,int uptodate)244 static void end_buffer_async_read(struct buffer_head *bh, int uptodate)
245 {
246 	unsigned long flags;
247 	struct buffer_head *first;
248 	struct buffer_head *tmp;
249 	struct page *page;
250 	int page_uptodate = 1;
251 
252 	BUG_ON(!buffer_async_read(bh));
253 
254 	page = bh->b_page;
255 	if (uptodate) {
256 		set_buffer_uptodate(bh);
257 	} else {
258 		clear_buffer_uptodate(bh);
259 		buffer_io_error(bh, ", async page read");
260 		SetPageError(page);
261 	}
262 
263 	/*
264 	 * Be _very_ careful from here on. Bad things can happen if
265 	 * two buffer heads end IO at almost the same time and both
266 	 * decide that the page is now completely done.
267 	 */
268 	first = page_buffers(page);
269 	spin_lock_irqsave(&first->b_uptodate_lock, flags);
270 	clear_buffer_async_read(bh);
271 	unlock_buffer(bh);
272 	tmp = bh;
273 	do {
274 		if (!buffer_uptodate(tmp))
275 			page_uptodate = 0;
276 		if (buffer_async_read(tmp)) {
277 			BUG_ON(!buffer_locked(tmp));
278 			goto still_busy;
279 		}
280 		tmp = tmp->b_this_page;
281 	} while (tmp != bh);
282 	spin_unlock_irqrestore(&first->b_uptodate_lock, flags);
283 
284 	/*
285 	 * If none of the buffers had errors and they are all
286 	 * uptodate then we can set the page uptodate.
287 	 */
288 	if (page_uptodate && !PageError(page))
289 		SetPageUptodate(page);
290 	unlock_page(page);
291 	return;
292 
293 still_busy:
294 	spin_unlock_irqrestore(&first->b_uptodate_lock, flags);
295 	return;
296 }
297 
298 struct decrypt_bh_ctx {
299 	struct work_struct work;
300 	struct buffer_head *bh;
301 };
302 
decrypt_bh(struct work_struct * work)303 static void decrypt_bh(struct work_struct *work)
304 {
305 	struct decrypt_bh_ctx *ctx =
306 		container_of(work, struct decrypt_bh_ctx, work);
307 	struct buffer_head *bh = ctx->bh;
308 	int err;
309 
310 	err = fscrypt_decrypt_pagecache_blocks(bh->b_page, bh->b_size,
311 					       bh_offset(bh));
312 	end_buffer_async_read(bh, err == 0);
313 	kfree(ctx);
314 }
315 
316 /*
317  * I/O completion handler for block_read_full_folio() - pages
318  * which come unlocked at the end of I/O.
319  */
end_buffer_async_read_io(struct buffer_head * bh,int uptodate)320 static void end_buffer_async_read_io(struct buffer_head *bh, int uptodate)
321 {
322 	/* Decrypt if needed */
323 	if (uptodate &&
324 	    fscrypt_inode_uses_fs_layer_crypto(bh->b_page->mapping->host)) {
325 		struct decrypt_bh_ctx *ctx = kmalloc(sizeof(*ctx), GFP_ATOMIC);
326 
327 		if (ctx) {
328 			INIT_WORK(&ctx->work, decrypt_bh);
329 			ctx->bh = bh;
330 			fscrypt_enqueue_decrypt_work(&ctx->work);
331 			return;
332 		}
333 		uptodate = 0;
334 	}
335 	end_buffer_async_read(bh, uptodate);
336 }
337 
338 /*
339  * Completion handler for block_write_full_page() - pages which are unlocked
340  * during I/O, and which have PageWriteback cleared upon I/O completion.
341  */
end_buffer_async_write(struct buffer_head * bh,int uptodate)342 void end_buffer_async_write(struct buffer_head *bh, int uptodate)
343 {
344 	unsigned long flags;
345 	struct buffer_head *first;
346 	struct buffer_head *tmp;
347 	struct page *page;
348 
349 	BUG_ON(!buffer_async_write(bh));
350 
351 	page = bh->b_page;
352 	if (uptodate) {
353 		set_buffer_uptodate(bh);
354 	} else {
355 		buffer_io_error(bh, ", lost async page write");
356 		mark_buffer_write_io_error(bh);
357 		clear_buffer_uptodate(bh);
358 		SetPageError(page);
359 	}
360 
361 	first = page_buffers(page);
362 	spin_lock_irqsave(&first->b_uptodate_lock, flags);
363 
364 	clear_buffer_async_write(bh);
365 	unlock_buffer(bh);
366 	tmp = bh->b_this_page;
367 	while (tmp != bh) {
368 		if (buffer_async_write(tmp)) {
369 			BUG_ON(!buffer_locked(tmp));
370 			goto still_busy;
371 		}
372 		tmp = tmp->b_this_page;
373 	}
374 	spin_unlock_irqrestore(&first->b_uptodate_lock, flags);
375 	end_page_writeback(page);
376 	return;
377 
378 still_busy:
379 	spin_unlock_irqrestore(&first->b_uptodate_lock, flags);
380 	return;
381 }
382 EXPORT_SYMBOL(end_buffer_async_write);
383 
384 /*
385  * If a page's buffers are under async readin (end_buffer_async_read
386  * completion) then there is a possibility that another thread of
387  * control could lock one of the buffers after it has completed
388  * but while some of the other buffers have not completed.  This
389  * locked buffer would confuse end_buffer_async_read() into not unlocking
390  * the page.  So the absence of BH_Async_Read tells end_buffer_async_read()
391  * that this buffer is not under async I/O.
392  *
393  * The page comes unlocked when it has no locked buffer_async buffers
394  * left.
395  *
396  * PageLocked prevents anyone starting new async I/O reads any of
397  * the buffers.
398  *
399  * PageWriteback is used to prevent simultaneous writeout of the same
400  * page.
401  *
402  * PageLocked prevents anyone from starting writeback of a page which is
403  * under read I/O (PageWriteback is only ever set against a locked page).
404  */
mark_buffer_async_read(struct buffer_head * bh)405 static void mark_buffer_async_read(struct buffer_head *bh)
406 {
407 	bh->b_end_io = end_buffer_async_read_io;
408 	set_buffer_async_read(bh);
409 }
410 
mark_buffer_async_write_endio(struct buffer_head * bh,bh_end_io_t * handler)411 static void mark_buffer_async_write_endio(struct buffer_head *bh,
412 					  bh_end_io_t *handler)
413 {
414 	bh->b_end_io = handler;
415 	set_buffer_async_write(bh);
416 }
417 
mark_buffer_async_write(struct buffer_head * bh)418 void mark_buffer_async_write(struct buffer_head *bh)
419 {
420 	mark_buffer_async_write_endio(bh, end_buffer_async_write);
421 }
422 EXPORT_SYMBOL(mark_buffer_async_write);
423 
424 
425 /*
426  * fs/buffer.c contains helper functions for buffer-backed address space's
427  * fsync functions.  A common requirement for buffer-based filesystems is
428  * that certain data from the backing blockdev needs to be written out for
429  * a successful fsync().  For example, ext2 indirect blocks need to be
430  * written back and waited upon before fsync() returns.
431  *
432  * The functions mark_buffer_inode_dirty(), fsync_inode_buffers(),
433  * inode_has_buffers() and invalidate_inode_buffers() are provided for the
434  * management of a list of dependent buffers at ->i_mapping->private_list.
435  *
436  * Locking is a little subtle: try_to_free_buffers() will remove buffers
437  * from their controlling inode's queue when they are being freed.  But
438  * try_to_free_buffers() will be operating against the *blockdev* mapping
439  * at the time, not against the S_ISREG file which depends on those buffers.
440  * So the locking for private_list is via the private_lock in the address_space
441  * which backs the buffers.  Which is different from the address_space
442  * against which the buffers are listed.  So for a particular address_space,
443  * mapping->private_lock does *not* protect mapping->private_list!  In fact,
444  * mapping->private_list will always be protected by the backing blockdev's
445  * ->private_lock.
446  *
447  * Which introduces a requirement: all buffers on an address_space's
448  * ->private_list must be from the same address_space: the blockdev's.
449  *
450  * address_spaces which do not place buffers at ->private_list via these
451  * utility functions are free to use private_lock and private_list for
452  * whatever they want.  The only requirement is that list_empty(private_list)
453  * be true at clear_inode() time.
454  *
455  * FIXME: clear_inode should not call invalidate_inode_buffers().  The
456  * filesystems should do that.  invalidate_inode_buffers() should just go
457  * BUG_ON(!list_empty).
458  *
459  * FIXME: mark_buffer_dirty_inode() is a data-plane operation.  It should
460  * take an address_space, not an inode.  And it should be called
461  * mark_buffer_dirty_fsync() to clearly define why those buffers are being
462  * queued up.
463  *
464  * FIXME: mark_buffer_dirty_inode() doesn't need to add the buffer to the
465  * list if it is already on a list.  Because if the buffer is on a list,
466  * it *must* already be on the right one.  If not, the filesystem is being
467  * silly.  This will save a ton of locking.  But first we have to ensure
468  * that buffers are taken *off* the old inode's list when they are freed
469  * (presumably in truncate).  That requires careful auditing of all
470  * filesystems (do it inside bforget()).  It could also be done by bringing
471  * b_inode back.
472  */
473 
474 /*
475  * The buffer's backing address_space's private_lock must be held
476  */
__remove_assoc_queue(struct buffer_head * bh)477 static void __remove_assoc_queue(struct buffer_head *bh)
478 {
479 	list_del_init(&bh->b_assoc_buffers);
480 	WARN_ON(!bh->b_assoc_map);
481 	bh->b_assoc_map = NULL;
482 }
483 
inode_has_buffers(struct inode * inode)484 int inode_has_buffers(struct inode *inode)
485 {
486 	return !list_empty(&inode->i_data.private_list);
487 }
488 
489 /*
490  * osync is designed to support O_SYNC io.  It waits synchronously for
491  * all already-submitted IO to complete, but does not queue any new
492  * writes to the disk.
493  *
494  * To do O_SYNC writes, just queue the buffer writes with ll_rw_block as
495  * you dirty the buffers, and then use osync_inode_buffers to wait for
496  * completion.  Any other dirty buffers which are not yet queued for
497  * write will not be flushed to disk by the osync.
498  */
osync_buffers_list(spinlock_t * lock,struct list_head * list)499 static int osync_buffers_list(spinlock_t *lock, struct list_head *list)
500 {
501 	struct buffer_head *bh;
502 	struct list_head *p;
503 	int err = 0;
504 
505 	spin_lock(lock);
506 repeat:
507 	list_for_each_prev(p, list) {
508 		bh = BH_ENTRY(p);
509 		if (buffer_locked(bh)) {
510 			get_bh(bh);
511 			spin_unlock(lock);
512 			wait_on_buffer(bh);
513 			if (!buffer_uptodate(bh))
514 				err = -EIO;
515 			brelse(bh);
516 			spin_lock(lock);
517 			goto repeat;
518 		}
519 	}
520 	spin_unlock(lock);
521 	return err;
522 }
523 
emergency_thaw_bdev(struct super_block * sb)524 void emergency_thaw_bdev(struct super_block *sb)
525 {
526 	while (sb->s_bdev && !thaw_bdev(sb->s_bdev))
527 		printk(KERN_WARNING "Emergency Thaw on %pg\n", sb->s_bdev);
528 }
529 
530 /**
531  * sync_mapping_buffers - write out & wait upon a mapping's "associated" buffers
532  * @mapping: the mapping which wants those buffers written
533  *
534  * Starts I/O against the buffers at mapping->private_list, and waits upon
535  * that I/O.
536  *
537  * Basically, this is a convenience function for fsync().
538  * @mapping is a file or directory which needs those buffers to be written for
539  * a successful fsync().
540  */
sync_mapping_buffers(struct address_space * mapping)541 int sync_mapping_buffers(struct address_space *mapping)
542 {
543 	struct address_space *buffer_mapping = mapping->private_data;
544 
545 	if (buffer_mapping == NULL || list_empty(&mapping->private_list))
546 		return 0;
547 
548 	return fsync_buffers_list(&buffer_mapping->private_lock,
549 					&mapping->private_list);
550 }
551 EXPORT_SYMBOL(sync_mapping_buffers);
552 
553 /*
554  * Called when we've recently written block `bblock', and it is known that
555  * `bblock' was for a buffer_boundary() buffer.  This means that the block at
556  * `bblock + 1' is probably a dirty indirect block.  Hunt it down and, if it's
557  * dirty, schedule it for IO.  So that indirects merge nicely with their data.
558  */
write_boundary_block(struct block_device * bdev,sector_t bblock,unsigned blocksize)559 void write_boundary_block(struct block_device *bdev,
560 			sector_t bblock, unsigned blocksize)
561 {
562 	struct buffer_head *bh = __find_get_block(bdev, bblock + 1, blocksize);
563 	if (bh) {
564 		if (buffer_dirty(bh))
565 			ll_rw_block(REQ_OP_WRITE, 0, 1, &bh);
566 		put_bh(bh);
567 	}
568 }
569 
mark_buffer_dirty_inode(struct buffer_head * bh,struct inode * inode)570 void mark_buffer_dirty_inode(struct buffer_head *bh, struct inode *inode)
571 {
572 	struct address_space *mapping = inode->i_mapping;
573 	struct address_space *buffer_mapping = bh->b_page->mapping;
574 
575 	mark_buffer_dirty(bh);
576 	if (!mapping->private_data) {
577 		mapping->private_data = buffer_mapping;
578 	} else {
579 		BUG_ON(mapping->private_data != buffer_mapping);
580 	}
581 	if (!bh->b_assoc_map) {
582 		spin_lock(&buffer_mapping->private_lock);
583 		list_move_tail(&bh->b_assoc_buffers,
584 				&mapping->private_list);
585 		bh->b_assoc_map = mapping;
586 		spin_unlock(&buffer_mapping->private_lock);
587 	}
588 }
589 EXPORT_SYMBOL(mark_buffer_dirty_inode);
590 
591 /*
592  * Add a page to the dirty page list.
593  *
594  * It is a sad fact of life that this function is called from several places
595  * deeply under spinlocking.  It may not sleep.
596  *
597  * If the page has buffers, the uptodate buffers are set dirty, to preserve
598  * dirty-state coherency between the page and the buffers.  It the page does
599  * not have buffers then when they are later attached they will all be set
600  * dirty.
601  *
602  * The buffers are dirtied before the page is dirtied.  There's a small race
603  * window in which a writepage caller may see the page cleanness but not the
604  * buffer dirtiness.  That's fine.  If this code were to set the page dirty
605  * before the buffers, a concurrent writepage caller could clear the page dirty
606  * bit, see a bunch of clean buffers and we'd end up with dirty buffers/clean
607  * page on the dirty page list.
608  *
609  * We use private_lock to lock against try_to_free_buffers while using the
610  * page's buffer list.  Also use this to protect against clean buffers being
611  * added to the page after it was set dirty.
612  *
613  * FIXME: may need to call ->reservepage here as well.  That's rather up to the
614  * address_space though.
615  */
block_dirty_folio(struct address_space * mapping,struct folio * folio)616 bool block_dirty_folio(struct address_space *mapping, struct folio *folio)
617 {
618 	struct buffer_head *head;
619 	bool newly_dirty;
620 
621 	spin_lock(&mapping->private_lock);
622 	head = folio_buffers(folio);
623 	if (head) {
624 		struct buffer_head *bh = head;
625 
626 		do {
627 			set_buffer_dirty(bh);
628 			bh = bh->b_this_page;
629 		} while (bh != head);
630 	}
631 	/*
632 	 * Lock out page's memcg migration to keep PageDirty
633 	 * synchronized with per-memcg dirty page counters.
634 	 */
635 	folio_memcg_lock(folio);
636 	newly_dirty = !folio_test_set_dirty(folio);
637 	spin_unlock(&mapping->private_lock);
638 
639 	if (newly_dirty)
640 		__folio_mark_dirty(folio, mapping, 1);
641 
642 	folio_memcg_unlock(folio);
643 
644 	if (newly_dirty)
645 		__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
646 
647 	return newly_dirty;
648 }
649 EXPORT_SYMBOL(block_dirty_folio);
650 
651 /*
652  * Write out and wait upon a list of buffers.
653  *
654  * We have conflicting pressures: we want to make sure that all
655  * initially dirty buffers get waited on, but that any subsequently
656  * dirtied buffers don't.  After all, we don't want fsync to last
657  * forever if somebody is actively writing to the file.
658  *
659  * Do this in two main stages: first we copy dirty buffers to a
660  * temporary inode list, queueing the writes as we go.  Then we clean
661  * up, waiting for those writes to complete.
662  *
663  * During this second stage, any subsequent updates to the file may end
664  * up refiling the buffer on the original inode's dirty list again, so
665  * there is a chance we will end up with a buffer queued for write but
666  * not yet completed on that list.  So, as a final cleanup we go through
667  * the osync code to catch these locked, dirty buffers without requeuing
668  * any newly dirty buffers for write.
669  */
fsync_buffers_list(spinlock_t * lock,struct list_head * list)670 static int fsync_buffers_list(spinlock_t *lock, struct list_head *list)
671 {
672 	struct buffer_head *bh;
673 	struct list_head tmp;
674 	struct address_space *mapping;
675 	int err = 0, err2;
676 	struct blk_plug plug;
677 
678 	INIT_LIST_HEAD(&tmp);
679 	blk_start_plug(&plug);
680 
681 	spin_lock(lock);
682 	while (!list_empty(list)) {
683 		bh = BH_ENTRY(list->next);
684 		mapping = bh->b_assoc_map;
685 		__remove_assoc_queue(bh);
686 		/* Avoid race with mark_buffer_dirty_inode() which does
687 		 * a lockless check and we rely on seeing the dirty bit */
688 		smp_mb();
689 		if (buffer_dirty(bh) || buffer_locked(bh)) {
690 			list_add(&bh->b_assoc_buffers, &tmp);
691 			bh->b_assoc_map = mapping;
692 			if (buffer_dirty(bh)) {
693 				get_bh(bh);
694 				spin_unlock(lock);
695 				/*
696 				 * Ensure any pending I/O completes so that
697 				 * write_dirty_buffer() actually writes the
698 				 * current contents - it is a noop if I/O is
699 				 * still in flight on potentially older
700 				 * contents.
701 				 */
702 				write_dirty_buffer(bh, REQ_SYNC);
703 
704 				/*
705 				 * Kick off IO for the previous mapping. Note
706 				 * that we will not run the very last mapping,
707 				 * wait_on_buffer() will do that for us
708 				 * through sync_buffer().
709 				 */
710 				brelse(bh);
711 				spin_lock(lock);
712 			}
713 		}
714 	}
715 
716 	spin_unlock(lock);
717 	blk_finish_plug(&plug);
718 	spin_lock(lock);
719 
720 	while (!list_empty(&tmp)) {
721 		bh = BH_ENTRY(tmp.prev);
722 		get_bh(bh);
723 		mapping = bh->b_assoc_map;
724 		__remove_assoc_queue(bh);
725 		/* Avoid race with mark_buffer_dirty_inode() which does
726 		 * a lockless check and we rely on seeing the dirty bit */
727 		smp_mb();
728 		if (buffer_dirty(bh)) {
729 			list_add(&bh->b_assoc_buffers,
730 				 &mapping->private_list);
731 			bh->b_assoc_map = mapping;
732 		}
733 		spin_unlock(lock);
734 		wait_on_buffer(bh);
735 		if (!buffer_uptodate(bh))
736 			err = -EIO;
737 		brelse(bh);
738 		spin_lock(lock);
739 	}
740 
741 	spin_unlock(lock);
742 	err2 = osync_buffers_list(lock, list);
743 	if (err)
744 		return err;
745 	else
746 		return err2;
747 }
748 
749 /*
750  * Invalidate any and all dirty buffers on a given inode.  We are
751  * probably unmounting the fs, but that doesn't mean we have already
752  * done a sync().  Just drop the buffers from the inode list.
753  *
754  * NOTE: we take the inode's blockdev's mapping's private_lock.  Which
755  * assumes that all the buffers are against the blockdev.  Not true
756  * for reiserfs.
757  */
invalidate_inode_buffers(struct inode * inode)758 void invalidate_inode_buffers(struct inode *inode)
759 {
760 	if (inode_has_buffers(inode)) {
761 		struct address_space *mapping = &inode->i_data;
762 		struct list_head *list = &mapping->private_list;
763 		struct address_space *buffer_mapping = mapping->private_data;
764 
765 		spin_lock(&buffer_mapping->private_lock);
766 		while (!list_empty(list))
767 			__remove_assoc_queue(BH_ENTRY(list->next));
768 		spin_unlock(&buffer_mapping->private_lock);
769 	}
770 }
771 EXPORT_SYMBOL(invalidate_inode_buffers);
772 
773 /*
774  * Remove any clean buffers from the inode's buffer list.  This is called
775  * when we're trying to free the inode itself.  Those buffers can pin it.
776  *
777  * Returns true if all buffers were removed.
778  */
remove_inode_buffers(struct inode * inode)779 int remove_inode_buffers(struct inode *inode)
780 {
781 	int ret = 1;
782 
783 	if (inode_has_buffers(inode)) {
784 		struct address_space *mapping = &inode->i_data;
785 		struct list_head *list = &mapping->private_list;
786 		struct address_space *buffer_mapping = mapping->private_data;
787 
788 		spin_lock(&buffer_mapping->private_lock);
789 		while (!list_empty(list)) {
790 			struct buffer_head *bh = BH_ENTRY(list->next);
791 			if (buffer_dirty(bh)) {
792 				ret = 0;
793 				break;
794 			}
795 			__remove_assoc_queue(bh);
796 		}
797 		spin_unlock(&buffer_mapping->private_lock);
798 	}
799 	return ret;
800 }
801 
802 /*
803  * Create the appropriate buffers when given a page for data area and
804  * the size of each buffer.. Use the bh->b_this_page linked list to
805  * follow the buffers created.  Return NULL if unable to create more
806  * buffers.
807  *
808  * The retry flag is used to differentiate async IO (paging, swapping)
809  * which may not fail from ordinary buffer allocations.
810  */
alloc_page_buffers(struct page * page,unsigned long size,bool retry)811 struct buffer_head *alloc_page_buffers(struct page *page, unsigned long size,
812 		bool retry)
813 {
814 	struct buffer_head *bh, *head;
815 	gfp_t gfp = GFP_NOFS | __GFP_ACCOUNT;
816 	long offset;
817 	struct mem_cgroup *memcg, *old_memcg;
818 
819 	if (retry)
820 		gfp |= __GFP_NOFAIL;
821 
822 	/* The page lock pins the memcg */
823 	memcg = page_memcg(page);
824 	old_memcg = set_active_memcg(memcg);
825 
826 	head = NULL;
827 	offset = PAGE_SIZE;
828 	while ((offset -= size) >= 0) {
829 		bh = alloc_buffer_head(gfp);
830 		if (!bh)
831 			goto no_grow;
832 
833 		bh->b_this_page = head;
834 		bh->b_blocknr = -1;
835 		head = bh;
836 
837 		bh->b_size = size;
838 
839 		/* Link the buffer to its page */
840 		set_bh_page(bh, page, offset);
841 	}
842 out:
843 	set_active_memcg(old_memcg);
844 	return head;
845 /*
846  * In case anything failed, we just free everything we got.
847  */
848 no_grow:
849 	if (head) {
850 		do {
851 			bh = head;
852 			head = head->b_this_page;
853 			free_buffer_head(bh);
854 		} while (head);
855 	}
856 
857 	goto out;
858 }
859 EXPORT_SYMBOL_GPL(alloc_page_buffers);
860 
861 static inline void
link_dev_buffers(struct page * page,struct buffer_head * head)862 link_dev_buffers(struct page *page, struct buffer_head *head)
863 {
864 	struct buffer_head *bh, *tail;
865 
866 	bh = head;
867 	do {
868 		tail = bh;
869 		bh = bh->b_this_page;
870 	} while (bh);
871 	tail->b_this_page = head;
872 	attach_page_private(page, head);
873 }
874 
blkdev_max_block(struct block_device * bdev,unsigned int size)875 static sector_t blkdev_max_block(struct block_device *bdev, unsigned int size)
876 {
877 	sector_t retval = ~((sector_t)0);
878 	loff_t sz = bdev_nr_bytes(bdev);
879 
880 	if (sz) {
881 		unsigned int sizebits = blksize_bits(size);
882 		retval = (sz >> sizebits);
883 	}
884 	return retval;
885 }
886 
887 /*
888  * Initialise the state of a blockdev page's buffers.
889  */
890 static sector_t
init_page_buffers(struct page * page,struct block_device * bdev,sector_t block,int size)891 init_page_buffers(struct page *page, struct block_device *bdev,
892 			sector_t block, int size)
893 {
894 	struct buffer_head *head = page_buffers(page);
895 	struct buffer_head *bh = head;
896 	int uptodate = PageUptodate(page);
897 	sector_t end_block = blkdev_max_block(bdev, size);
898 
899 	do {
900 		if (!buffer_mapped(bh)) {
901 			bh->b_end_io = NULL;
902 			bh->b_private = NULL;
903 			bh->b_bdev = bdev;
904 			bh->b_blocknr = block;
905 			if (uptodate)
906 				set_buffer_uptodate(bh);
907 			if (block < end_block)
908 				set_buffer_mapped(bh);
909 		}
910 		block++;
911 		bh = bh->b_this_page;
912 	} while (bh != head);
913 
914 	/*
915 	 * Caller needs to validate requested block against end of device.
916 	 */
917 	return end_block;
918 }
919 
920 /*
921  * Create the page-cache page that contains the requested block.
922  *
923  * This is used purely for blockdev mappings.
924  */
925 static int
grow_dev_page(struct block_device * bdev,sector_t block,pgoff_t index,int size,int sizebits,gfp_t gfp)926 grow_dev_page(struct block_device *bdev, sector_t block,
927 	      pgoff_t index, int size, int sizebits, gfp_t gfp)
928 {
929 	struct inode *inode = bdev->bd_inode;
930 	struct page *page;
931 	struct buffer_head *bh;
932 	sector_t end_block;
933 	int ret = 0;
934 	gfp_t gfp_mask;
935 
936 	gfp_mask = mapping_gfp_constraint(inode->i_mapping, ~__GFP_FS) | gfp;
937 
938 	/*
939 	 * XXX: __getblk_slow() can not really deal with failure and
940 	 * will endlessly loop on improvised global reclaim.  Prefer
941 	 * looping in the allocator rather than here, at least that
942 	 * code knows what it's doing.
943 	 */
944 	gfp_mask |= __GFP_NOFAIL;
945 
946 	page = find_or_create_page(inode->i_mapping, index, gfp_mask);
947 
948 	BUG_ON(!PageLocked(page));
949 
950 	if (page_has_buffers(page)) {
951 		bh = page_buffers(page);
952 		if (bh->b_size == size) {
953 			end_block = init_page_buffers(page, bdev,
954 						(sector_t)index << sizebits,
955 						size);
956 			goto done;
957 		}
958 		if (!try_to_free_buffers(page_folio(page)))
959 			goto failed;
960 	}
961 
962 	/*
963 	 * Allocate some buffers for this page
964 	 */
965 	bh = alloc_page_buffers(page, size, true);
966 
967 	/*
968 	 * Link the page to the buffers and initialise them.  Take the
969 	 * lock to be atomic wrt __find_get_block(), which does not
970 	 * run under the page lock.
971 	 */
972 	spin_lock(&inode->i_mapping->private_lock);
973 	link_dev_buffers(page, bh);
974 	end_block = init_page_buffers(page, bdev, (sector_t)index << sizebits,
975 			size);
976 	spin_unlock(&inode->i_mapping->private_lock);
977 done:
978 	ret = (block < end_block) ? 1 : -ENXIO;
979 failed:
980 	unlock_page(page);
981 	put_page(page);
982 	return ret;
983 }
984 
985 /*
986  * Create buffers for the specified block device block's page.  If
987  * that page was dirty, the buffers are set dirty also.
988  */
989 static int
grow_buffers(struct block_device * bdev,sector_t block,int size,gfp_t gfp)990 grow_buffers(struct block_device *bdev, sector_t block, int size, gfp_t gfp)
991 {
992 	pgoff_t index;
993 	int sizebits;
994 
995 	sizebits = PAGE_SHIFT - __ffs(size);
996 	index = block >> sizebits;
997 
998 	/*
999 	 * Check for a block which wants to lie outside our maximum possible
1000 	 * pagecache index.  (this comparison is done using sector_t types).
1001 	 */
1002 	if (unlikely(index != block >> sizebits)) {
1003 		printk(KERN_ERR "%s: requested out-of-range block %llu for "
1004 			"device %pg\n",
1005 			__func__, (unsigned long long)block,
1006 			bdev);
1007 		return -EIO;
1008 	}
1009 
1010 	/* Create a page with the proper size buffers.. */
1011 	return grow_dev_page(bdev, block, index, size, sizebits, gfp);
1012 }
1013 
1014 static struct buffer_head *
__getblk_slow(struct block_device * bdev,sector_t block,unsigned size,gfp_t gfp)1015 __getblk_slow(struct block_device *bdev, sector_t block,
1016 	     unsigned size, gfp_t gfp)
1017 {
1018 	/* Size must be multiple of hard sectorsize */
1019 	if (unlikely(size & (bdev_logical_block_size(bdev)-1) ||
1020 			(size < 512 || size > PAGE_SIZE))) {
1021 		printk(KERN_ERR "getblk(): invalid block size %d requested\n",
1022 					size);
1023 		printk(KERN_ERR "logical block size: %d\n",
1024 					bdev_logical_block_size(bdev));
1025 
1026 		dump_stack();
1027 		return NULL;
1028 	}
1029 
1030 	for (;;) {
1031 		struct buffer_head *bh;
1032 		int ret;
1033 
1034 		bh = __find_get_block(bdev, block, size);
1035 		if (bh)
1036 			return bh;
1037 
1038 		ret = grow_buffers(bdev, block, size, gfp);
1039 		if (ret < 0)
1040 			return NULL;
1041 	}
1042 }
1043 
1044 /*
1045  * The relationship between dirty buffers and dirty pages:
1046  *
1047  * Whenever a page has any dirty buffers, the page's dirty bit is set, and
1048  * the page is tagged dirty in the page cache.
1049  *
1050  * At all times, the dirtiness of the buffers represents the dirtiness of
1051  * subsections of the page.  If the page has buffers, the page dirty bit is
1052  * merely a hint about the true dirty state.
1053  *
1054  * When a page is set dirty in its entirety, all its buffers are marked dirty
1055  * (if the page has buffers).
1056  *
1057  * When a buffer is marked dirty, its page is dirtied, but the page's other
1058  * buffers are not.
1059  *
1060  * Also.  When blockdev buffers are explicitly read with bread(), they
1061  * individually become uptodate.  But their backing page remains not
1062  * uptodate - even if all of its buffers are uptodate.  A subsequent
1063  * block_read_full_folio() against that folio will discover all the uptodate
1064  * buffers, will set the folio uptodate and will perform no I/O.
1065  */
1066 
1067 /**
1068  * mark_buffer_dirty - mark a buffer_head as needing writeout
1069  * @bh: the buffer_head to mark dirty
1070  *
1071  * mark_buffer_dirty() will set the dirty bit against the buffer, then set
1072  * its backing page dirty, then tag the page as dirty in the page cache
1073  * and then attach the address_space's inode to its superblock's dirty
1074  * inode list.
1075  *
1076  * mark_buffer_dirty() is atomic.  It takes bh->b_page->mapping->private_lock,
1077  * i_pages lock and mapping->host->i_lock.
1078  */
mark_buffer_dirty(struct buffer_head * bh)1079 void mark_buffer_dirty(struct buffer_head *bh)
1080 {
1081 	WARN_ON_ONCE(!buffer_uptodate(bh));
1082 
1083 	trace_block_dirty_buffer(bh);
1084 
1085 	/*
1086 	 * Very *carefully* optimize the it-is-already-dirty case.
1087 	 *
1088 	 * Don't let the final "is it dirty" escape to before we
1089 	 * perhaps modified the buffer.
1090 	 */
1091 	if (buffer_dirty(bh)) {
1092 		smp_mb();
1093 		if (buffer_dirty(bh))
1094 			return;
1095 	}
1096 
1097 	if (!test_set_buffer_dirty(bh)) {
1098 		struct page *page = bh->b_page;
1099 		struct address_space *mapping = NULL;
1100 
1101 		lock_page_memcg(page);
1102 		if (!TestSetPageDirty(page)) {
1103 			mapping = page_mapping(page);
1104 			if (mapping)
1105 				__set_page_dirty(page, mapping, 0);
1106 		}
1107 		unlock_page_memcg(page);
1108 		if (mapping)
1109 			__mark_inode_dirty(mapping->host, I_DIRTY_PAGES);
1110 	}
1111 }
1112 EXPORT_SYMBOL(mark_buffer_dirty);
1113 
mark_buffer_write_io_error(struct buffer_head * bh)1114 void mark_buffer_write_io_error(struct buffer_head *bh)
1115 {
1116 	struct super_block *sb;
1117 
1118 	set_buffer_write_io_error(bh);
1119 	/* FIXME: do we need to set this in both places? */
1120 	if (bh->b_page && bh->b_page->mapping)
1121 		mapping_set_error(bh->b_page->mapping, -EIO);
1122 	if (bh->b_assoc_map)
1123 		mapping_set_error(bh->b_assoc_map, -EIO);
1124 	rcu_read_lock();
1125 	sb = READ_ONCE(bh->b_bdev->bd_super);
1126 	if (sb)
1127 		errseq_set(&sb->s_wb_err, -EIO);
1128 	rcu_read_unlock();
1129 }
1130 EXPORT_SYMBOL(mark_buffer_write_io_error);
1131 
1132 /*
1133  * Decrement a buffer_head's reference count.  If all buffers against a page
1134  * have zero reference count, are clean and unlocked, and if the page is clean
1135  * and unlocked then try_to_free_buffers() may strip the buffers from the page
1136  * in preparation for freeing it (sometimes, rarely, buffers are removed from
1137  * a page but it ends up not being freed, and buffers may later be reattached).
1138  */
__brelse(struct buffer_head * buf)1139 void __brelse(struct buffer_head * buf)
1140 {
1141 	if (atomic_read(&buf->b_count)) {
1142 		put_bh(buf);
1143 		return;
1144 	}
1145 	WARN(1, KERN_ERR "VFS: brelse: Trying to free free buffer\n");
1146 }
1147 EXPORT_SYMBOL(__brelse);
1148 
1149 /*
1150  * bforget() is like brelse(), except it discards any
1151  * potentially dirty data.
1152  */
__bforget(struct buffer_head * bh)1153 void __bforget(struct buffer_head *bh)
1154 {
1155 	clear_buffer_dirty(bh);
1156 	if (bh->b_assoc_map) {
1157 		struct address_space *buffer_mapping = bh->b_page->mapping;
1158 
1159 		spin_lock(&buffer_mapping->private_lock);
1160 		list_del_init(&bh->b_assoc_buffers);
1161 		bh->b_assoc_map = NULL;
1162 		spin_unlock(&buffer_mapping->private_lock);
1163 	}
1164 	__brelse(bh);
1165 }
1166 EXPORT_SYMBOL(__bforget);
1167 
__bread_slow(struct buffer_head * bh)1168 static struct buffer_head *__bread_slow(struct buffer_head *bh)
1169 {
1170 	lock_buffer(bh);
1171 	if (buffer_uptodate(bh)) {
1172 		unlock_buffer(bh);
1173 		return bh;
1174 	} else {
1175 		get_bh(bh);
1176 		bh->b_end_io = end_buffer_read_sync;
1177 		submit_bh(REQ_OP_READ, 0, bh);
1178 		wait_on_buffer(bh);
1179 		if (buffer_uptodate(bh))
1180 			return bh;
1181 	}
1182 	brelse(bh);
1183 	return NULL;
1184 }
1185 
1186 /*
1187  * Per-cpu buffer LRU implementation.  To reduce the cost of __find_get_block().
1188  * The bhs[] array is sorted - newest buffer is at bhs[0].  Buffers have their
1189  * refcount elevated by one when they're in an LRU.  A buffer can only appear
1190  * once in a particular CPU's LRU.  A single buffer can be present in multiple
1191  * CPU's LRUs at the same time.
1192  *
1193  * This is a transparent caching front-end to sb_bread(), sb_getblk() and
1194  * sb_find_get_block().
1195  *
1196  * The LRUs themselves only need locking against invalidate_bh_lrus.  We use
1197  * a local interrupt disable for that.
1198  */
1199 
1200 #define BH_LRU_SIZE	16
1201 
1202 struct bh_lru {
1203 	struct buffer_head *bhs[BH_LRU_SIZE];
1204 };
1205 
1206 static DEFINE_PER_CPU(struct bh_lru, bh_lrus) = {{ NULL }};
1207 
1208 #ifdef CONFIG_SMP
1209 #define bh_lru_lock()	local_irq_disable()
1210 #define bh_lru_unlock()	local_irq_enable()
1211 #else
1212 #define bh_lru_lock()	preempt_disable()
1213 #define bh_lru_unlock()	preempt_enable()
1214 #endif
1215 
check_irqs_on(void)1216 static inline void check_irqs_on(void)
1217 {
1218 #ifdef irqs_disabled
1219 	BUG_ON(irqs_disabled());
1220 #endif
1221 }
1222 
1223 /*
1224  * Install a buffer_head into this cpu's LRU.  If not already in the LRU, it is
1225  * inserted at the front, and the buffer_head at the back if any is evicted.
1226  * Or, if already in the LRU it is moved to the front.
1227  */
bh_lru_install(struct buffer_head * bh)1228 static void bh_lru_install(struct buffer_head *bh)
1229 {
1230 	struct buffer_head *evictee = bh;
1231 	struct bh_lru *b;
1232 	int i;
1233 
1234 	check_irqs_on();
1235 	bh_lru_lock();
1236 
1237 	/*
1238 	 * the refcount of buffer_head in bh_lru prevents dropping the
1239 	 * attached page(i.e., try_to_free_buffers) so it could cause
1240 	 * failing page migration.
1241 	 * Skip putting upcoming bh into bh_lru until migration is done.
1242 	 */
1243 	if (lru_cache_disabled()) {
1244 		bh_lru_unlock();
1245 		return;
1246 	}
1247 
1248 	b = this_cpu_ptr(&bh_lrus);
1249 	for (i = 0; i < BH_LRU_SIZE; i++) {
1250 		swap(evictee, b->bhs[i]);
1251 		if (evictee == bh) {
1252 			bh_lru_unlock();
1253 			return;
1254 		}
1255 	}
1256 
1257 	get_bh(bh);
1258 	bh_lru_unlock();
1259 	brelse(evictee);
1260 }
1261 
1262 /*
1263  * Look up the bh in this cpu's LRU.  If it's there, move it to the head.
1264  */
1265 static struct buffer_head *
lookup_bh_lru(struct block_device * bdev,sector_t block,unsigned size)1266 lookup_bh_lru(struct block_device *bdev, sector_t block, unsigned size)
1267 {
1268 	struct buffer_head *ret = NULL;
1269 	unsigned int i;
1270 
1271 	check_irqs_on();
1272 	bh_lru_lock();
1273 	for (i = 0; i < BH_LRU_SIZE; i++) {
1274 		struct buffer_head *bh = __this_cpu_read(bh_lrus.bhs[i]);
1275 
1276 		if (bh && bh->b_blocknr == block && bh->b_bdev == bdev &&
1277 		    bh->b_size == size) {
1278 			if (i) {
1279 				while (i) {
1280 					__this_cpu_write(bh_lrus.bhs[i],
1281 						__this_cpu_read(bh_lrus.bhs[i - 1]));
1282 					i--;
1283 				}
1284 				__this_cpu_write(bh_lrus.bhs[0], bh);
1285 			}
1286 			get_bh(bh);
1287 			ret = bh;
1288 			break;
1289 		}
1290 	}
1291 	bh_lru_unlock();
1292 	return ret;
1293 }
1294 
1295 /*
1296  * Perform a pagecache lookup for the matching buffer.  If it's there, refresh
1297  * it in the LRU and mark it as accessed.  If it is not present then return
1298  * NULL
1299  */
1300 struct buffer_head *
__find_get_block(struct block_device * bdev,sector_t block,unsigned size)1301 __find_get_block(struct block_device *bdev, sector_t block, unsigned size)
1302 {
1303 	struct buffer_head *bh = lookup_bh_lru(bdev, block, size);
1304 
1305 	if (bh == NULL) {
1306 		/* __find_get_block_slow will mark the page accessed */
1307 		bh = __find_get_block_slow(bdev, block);
1308 		if (bh)
1309 			bh_lru_install(bh);
1310 	} else
1311 		touch_buffer(bh);
1312 
1313 	return bh;
1314 }
1315 EXPORT_SYMBOL(__find_get_block);
1316 
1317 /*
1318  * __getblk_gfp() will locate (and, if necessary, create) the buffer_head
1319  * which corresponds to the passed block_device, block and size. The
1320  * returned buffer has its reference count incremented.
1321  *
1322  * __getblk_gfp() will lock up the machine if grow_dev_page's
1323  * try_to_free_buffers() attempt is failing.  FIXME, perhaps?
1324  */
1325 struct buffer_head *
__getblk_gfp(struct block_device * bdev,sector_t block,unsigned size,gfp_t gfp)1326 __getblk_gfp(struct block_device *bdev, sector_t block,
1327 	     unsigned size, gfp_t gfp)
1328 {
1329 	struct buffer_head *bh = __find_get_block(bdev, block, size);
1330 
1331 	might_sleep();
1332 	if (bh == NULL)
1333 		bh = __getblk_slow(bdev, block, size, gfp);
1334 	return bh;
1335 }
1336 EXPORT_SYMBOL(__getblk_gfp);
1337 
1338 /*
1339  * Do async read-ahead on a buffer..
1340  */
__breadahead(struct block_device * bdev,sector_t block,unsigned size)1341 void __breadahead(struct block_device *bdev, sector_t block, unsigned size)
1342 {
1343 	struct buffer_head *bh = __getblk(bdev, block, size);
1344 	if (likely(bh)) {
1345 		ll_rw_block(REQ_OP_READ, REQ_RAHEAD, 1, &bh);
1346 		brelse(bh);
1347 	}
1348 }
1349 EXPORT_SYMBOL(__breadahead);
1350 
__breadahead_gfp(struct block_device * bdev,sector_t block,unsigned size,gfp_t gfp)1351 void __breadahead_gfp(struct block_device *bdev, sector_t block, unsigned size,
1352 		      gfp_t gfp)
1353 {
1354 	struct buffer_head *bh = __getblk_gfp(bdev, block, size, gfp);
1355 	if (likely(bh)) {
1356 		ll_rw_block(REQ_OP_READ, REQ_RAHEAD, 1, &bh);
1357 		brelse(bh);
1358 	}
1359 }
1360 EXPORT_SYMBOL(__breadahead_gfp);
1361 
1362 /**
1363  *  __bread_gfp() - reads a specified block and returns the bh
1364  *  @bdev: the block_device to read from
1365  *  @block: number of block
1366  *  @size: size (in bytes) to read
1367  *  @gfp: page allocation flag
1368  *
1369  *  Reads a specified block, and returns buffer head that contains it.
1370  *  The page cache can be allocated from non-movable area
1371  *  not to prevent page migration if you set gfp to zero.
1372  *  It returns NULL if the block was unreadable.
1373  */
1374 struct buffer_head *
__bread_gfp(struct block_device * bdev,sector_t block,unsigned size,gfp_t gfp)1375 __bread_gfp(struct block_device *bdev, sector_t block,
1376 		   unsigned size, gfp_t gfp)
1377 {
1378 	struct buffer_head *bh = __getblk_gfp(bdev, block, size, gfp);
1379 
1380 	if (likely(bh) && !buffer_uptodate(bh))
1381 		bh = __bread_slow(bh);
1382 	return bh;
1383 }
1384 EXPORT_SYMBOL(__bread_gfp);
1385 
__invalidate_bh_lrus(struct bh_lru * b)1386 static void __invalidate_bh_lrus(struct bh_lru *b)
1387 {
1388 	int i;
1389 
1390 	for (i = 0; i < BH_LRU_SIZE; i++) {
1391 		brelse(b->bhs[i]);
1392 		b->bhs[i] = NULL;
1393 	}
1394 }
1395 /*
1396  * invalidate_bh_lrus() is called rarely - but not only at unmount.
1397  * This doesn't race because it runs in each cpu either in irq
1398  * or with preempt disabled.
1399  */
invalidate_bh_lru(void * arg)1400 static void invalidate_bh_lru(void *arg)
1401 {
1402 	struct bh_lru *b = &get_cpu_var(bh_lrus);
1403 
1404 	__invalidate_bh_lrus(b);
1405 	put_cpu_var(bh_lrus);
1406 }
1407 
has_bh_in_lru(int cpu,void * dummy)1408 bool has_bh_in_lru(int cpu, void *dummy)
1409 {
1410 	struct bh_lru *b = per_cpu_ptr(&bh_lrus, cpu);
1411 	int i;
1412 
1413 	for (i = 0; i < BH_LRU_SIZE; i++) {
1414 		if (b->bhs[i])
1415 			return true;
1416 	}
1417 
1418 	return false;
1419 }
1420 
invalidate_bh_lrus(void)1421 void invalidate_bh_lrus(void)
1422 {
1423 	on_each_cpu_cond(has_bh_in_lru, invalidate_bh_lru, NULL, 1);
1424 }
1425 EXPORT_SYMBOL_GPL(invalidate_bh_lrus);
1426 
1427 /*
1428  * It's called from workqueue context so we need a bh_lru_lock to close
1429  * the race with preemption/irq.
1430  */
invalidate_bh_lrus_cpu(void)1431 void invalidate_bh_lrus_cpu(void)
1432 {
1433 	struct bh_lru *b;
1434 
1435 	bh_lru_lock();
1436 	b = this_cpu_ptr(&bh_lrus);
1437 	__invalidate_bh_lrus(b);
1438 	bh_lru_unlock();
1439 }
1440 
set_bh_page(struct buffer_head * bh,struct page * page,unsigned long offset)1441 void set_bh_page(struct buffer_head *bh,
1442 		struct page *page, unsigned long offset)
1443 {
1444 	bh->b_page = page;
1445 	BUG_ON(offset >= PAGE_SIZE);
1446 	if (PageHighMem(page))
1447 		/*
1448 		 * This catches illegal uses and preserves the offset:
1449 		 */
1450 		bh->b_data = (char *)(0 + offset);
1451 	else
1452 		bh->b_data = page_address(page) + offset;
1453 }
1454 EXPORT_SYMBOL(set_bh_page);
1455 
1456 /*
1457  * Called when truncating a buffer on a page completely.
1458  */
1459 
1460 /* Bits that are cleared during an invalidate */
1461 #define BUFFER_FLAGS_DISCARD \
1462 	(1 << BH_Mapped | 1 << BH_New | 1 << BH_Req | \
1463 	 1 << BH_Delay | 1 << BH_Unwritten)
1464 
discard_buffer(struct buffer_head * bh)1465 static void discard_buffer(struct buffer_head * bh)
1466 {
1467 	unsigned long b_state, b_state_old;
1468 
1469 	lock_buffer(bh);
1470 	clear_buffer_dirty(bh);
1471 	bh->b_bdev = NULL;
1472 	b_state = bh->b_state;
1473 	for (;;) {
1474 		b_state_old = cmpxchg(&bh->b_state, b_state,
1475 				      (b_state & ~BUFFER_FLAGS_DISCARD));
1476 		if (b_state_old == b_state)
1477 			break;
1478 		b_state = b_state_old;
1479 	}
1480 	unlock_buffer(bh);
1481 }
1482 
1483 /**
1484  * block_invalidate_folio - Invalidate part or all of a buffer-backed folio.
1485  * @folio: The folio which is affected.
1486  * @offset: start of the range to invalidate
1487  * @length: length of the range to invalidate
1488  *
1489  * block_invalidate_folio() is called when all or part of the folio has been
1490  * invalidated by a truncate operation.
1491  *
1492  * block_invalidate_folio() does not have to release all buffers, but it must
1493  * ensure that no dirty buffer is left outside @offset and that no I/O
1494  * is underway against any of the blocks which are outside the truncation
1495  * point.  Because the caller is about to free (and possibly reuse) those
1496  * blocks on-disk.
1497  */
block_invalidate_folio(struct folio * folio,size_t offset,size_t length)1498 void block_invalidate_folio(struct folio *folio, size_t offset, size_t length)
1499 {
1500 	struct buffer_head *head, *bh, *next;
1501 	size_t curr_off = 0;
1502 	size_t stop = length + offset;
1503 
1504 	BUG_ON(!folio_test_locked(folio));
1505 
1506 	/*
1507 	 * Check for overflow
1508 	 */
1509 	BUG_ON(stop > folio_size(folio) || stop < length);
1510 
1511 	head = folio_buffers(folio);
1512 	if (!head)
1513 		return;
1514 
1515 	bh = head;
1516 	do {
1517 		size_t next_off = curr_off + bh->b_size;
1518 		next = bh->b_this_page;
1519 
1520 		/*
1521 		 * Are we still fully in range ?
1522 		 */
1523 		if (next_off > stop)
1524 			goto out;
1525 
1526 		/*
1527 		 * is this block fully invalidated?
1528 		 */
1529 		if (offset <= curr_off)
1530 			discard_buffer(bh);
1531 		curr_off = next_off;
1532 		bh = next;
1533 	} while (bh != head);
1534 
1535 	/*
1536 	 * We release buffers only if the entire folio is being invalidated.
1537 	 * The get_block cached value has been unconditionally invalidated,
1538 	 * so real IO is not possible anymore.
1539 	 */
1540 	if (length == folio_size(folio))
1541 		filemap_release_folio(folio, 0);
1542 out:
1543 	return;
1544 }
1545 EXPORT_SYMBOL(block_invalidate_folio);
1546 
1547 
1548 /*
1549  * We attach and possibly dirty the buffers atomically wrt
1550  * block_dirty_folio() via private_lock.  try_to_free_buffers
1551  * is already excluded via the page lock.
1552  */
create_empty_buffers(struct page * page,unsigned long blocksize,unsigned long b_state)1553 void create_empty_buffers(struct page *page,
1554 			unsigned long blocksize, unsigned long b_state)
1555 {
1556 	struct buffer_head *bh, *head, *tail;
1557 
1558 	head = alloc_page_buffers(page, blocksize, true);
1559 	bh = head;
1560 	do {
1561 		bh->b_state |= b_state;
1562 		tail = bh;
1563 		bh = bh->b_this_page;
1564 	} while (bh);
1565 	tail->b_this_page = head;
1566 
1567 	spin_lock(&page->mapping->private_lock);
1568 	if (PageUptodate(page) || PageDirty(page)) {
1569 		bh = head;
1570 		do {
1571 			if (PageDirty(page))
1572 				set_buffer_dirty(bh);
1573 			if (PageUptodate(page))
1574 				set_buffer_uptodate(bh);
1575 			bh = bh->b_this_page;
1576 		} while (bh != head);
1577 	}
1578 	attach_page_private(page, head);
1579 	spin_unlock(&page->mapping->private_lock);
1580 }
1581 EXPORT_SYMBOL(create_empty_buffers);
1582 
1583 /**
1584  * clean_bdev_aliases: clean a range of buffers in block device
1585  * @bdev: Block device to clean buffers in
1586  * @block: Start of a range of blocks to clean
1587  * @len: Number of blocks to clean
1588  *
1589  * We are taking a range of blocks for data and we don't want writeback of any
1590  * buffer-cache aliases starting from return from this function and until the
1591  * moment when something will explicitly mark the buffer dirty (hopefully that
1592  * will not happen until we will free that block ;-) We don't even need to mark
1593  * it not-uptodate - nobody can expect anything from a newly allocated buffer
1594  * anyway. We used to use unmap_buffer() for such invalidation, but that was
1595  * wrong. We definitely don't want to mark the alias unmapped, for example - it
1596  * would confuse anyone who might pick it with bread() afterwards...
1597  *
1598  * Also..  Note that bforget() doesn't lock the buffer.  So there can be
1599  * writeout I/O going on against recently-freed buffers.  We don't wait on that
1600  * I/O in bforget() - it's more efficient to wait on the I/O only if we really
1601  * need to.  That happens here.
1602  */
clean_bdev_aliases(struct block_device * bdev,sector_t block,sector_t len)1603 void clean_bdev_aliases(struct block_device *bdev, sector_t block, sector_t len)
1604 {
1605 	struct inode *bd_inode = bdev->bd_inode;
1606 	struct address_space *bd_mapping = bd_inode->i_mapping;
1607 	struct pagevec pvec;
1608 	pgoff_t index = block >> (PAGE_SHIFT - bd_inode->i_blkbits);
1609 	pgoff_t end;
1610 	int i, count;
1611 	struct buffer_head *bh;
1612 	struct buffer_head *head;
1613 
1614 	end = (block + len - 1) >> (PAGE_SHIFT - bd_inode->i_blkbits);
1615 	pagevec_init(&pvec);
1616 	while (pagevec_lookup_range(&pvec, bd_mapping, &index, end)) {
1617 		count = pagevec_count(&pvec);
1618 		for (i = 0; i < count; i++) {
1619 			struct page *page = pvec.pages[i];
1620 
1621 			if (!page_has_buffers(page))
1622 				continue;
1623 			/*
1624 			 * We use page lock instead of bd_mapping->private_lock
1625 			 * to pin buffers here since we can afford to sleep and
1626 			 * it scales better than a global spinlock lock.
1627 			 */
1628 			lock_page(page);
1629 			/* Recheck when the page is locked which pins bhs */
1630 			if (!page_has_buffers(page))
1631 				goto unlock_page;
1632 			head = page_buffers(page);
1633 			bh = head;
1634 			do {
1635 				if (!buffer_mapped(bh) || (bh->b_blocknr < block))
1636 					goto next;
1637 				if (bh->b_blocknr >= block + len)
1638 					break;
1639 				clear_buffer_dirty(bh);
1640 				wait_on_buffer(bh);
1641 				clear_buffer_req(bh);
1642 next:
1643 				bh = bh->b_this_page;
1644 			} while (bh != head);
1645 unlock_page:
1646 			unlock_page(page);
1647 		}
1648 		pagevec_release(&pvec);
1649 		cond_resched();
1650 		/* End of range already reached? */
1651 		if (index > end || !index)
1652 			break;
1653 	}
1654 }
1655 EXPORT_SYMBOL(clean_bdev_aliases);
1656 
1657 /*
1658  * Size is a power-of-two in the range 512..PAGE_SIZE,
1659  * and the case we care about most is PAGE_SIZE.
1660  *
1661  * So this *could* possibly be written with those
1662  * constraints in mind (relevant mostly if some
1663  * architecture has a slow bit-scan instruction)
1664  */
block_size_bits(unsigned int blocksize)1665 static inline int block_size_bits(unsigned int blocksize)
1666 {
1667 	return ilog2(blocksize);
1668 }
1669 
create_page_buffers(struct page * page,struct inode * inode,unsigned int b_state)1670 static struct buffer_head *create_page_buffers(struct page *page, struct inode *inode, unsigned int b_state)
1671 {
1672 	BUG_ON(!PageLocked(page));
1673 
1674 	if (!page_has_buffers(page))
1675 		create_empty_buffers(page, 1 << READ_ONCE(inode->i_blkbits),
1676 				     b_state);
1677 	return page_buffers(page);
1678 }
1679 
1680 /*
1681  * NOTE! All mapped/uptodate combinations are valid:
1682  *
1683  *	Mapped	Uptodate	Meaning
1684  *
1685  *	No	No		"unknown" - must do get_block()
1686  *	No	Yes		"hole" - zero-filled
1687  *	Yes	No		"allocated" - allocated on disk, not read in
1688  *	Yes	Yes		"valid" - allocated and up-to-date in memory.
1689  *
1690  * "Dirty" is valid only with the last case (mapped+uptodate).
1691  */
1692 
1693 /*
1694  * While block_write_full_page is writing back the dirty buffers under
1695  * the page lock, whoever dirtied the buffers may decide to clean them
1696  * again at any time.  We handle that by only looking at the buffer
1697  * state inside lock_buffer().
1698  *
1699  * If block_write_full_page() is called for regular writeback
1700  * (wbc->sync_mode == WB_SYNC_NONE) then it will redirty a page which has a
1701  * locked buffer.   This only can happen if someone has written the buffer
1702  * directly, with submit_bh().  At the address_space level PageWriteback
1703  * prevents this contention from occurring.
1704  *
1705  * If block_write_full_page() is called with wbc->sync_mode ==
1706  * WB_SYNC_ALL, the writes are posted using REQ_SYNC; this
1707  * causes the writes to be flagged as synchronous writes.
1708  */
__block_write_full_page(struct inode * inode,struct page * page,get_block_t * get_block,struct writeback_control * wbc,bh_end_io_t * handler)1709 int __block_write_full_page(struct inode *inode, struct page *page,
1710 			get_block_t *get_block, struct writeback_control *wbc,
1711 			bh_end_io_t *handler)
1712 {
1713 	int err;
1714 	sector_t block;
1715 	sector_t last_block;
1716 	struct buffer_head *bh, *head;
1717 	unsigned int blocksize, bbits;
1718 	int nr_underway = 0;
1719 	int write_flags = wbc_to_write_flags(wbc);
1720 
1721 	head = create_page_buffers(page, inode,
1722 					(1 << BH_Dirty)|(1 << BH_Uptodate));
1723 
1724 	/*
1725 	 * Be very careful.  We have no exclusion from block_dirty_folio
1726 	 * here, and the (potentially unmapped) buffers may become dirty at
1727 	 * any time.  If a buffer becomes dirty here after we've inspected it
1728 	 * then we just miss that fact, and the page stays dirty.
1729 	 *
1730 	 * Buffers outside i_size may be dirtied by block_dirty_folio;
1731 	 * handle that here by just cleaning them.
1732 	 */
1733 
1734 	bh = head;
1735 	blocksize = bh->b_size;
1736 	bbits = block_size_bits(blocksize);
1737 
1738 	block = (sector_t)page->index << (PAGE_SHIFT - bbits);
1739 	last_block = (i_size_read(inode) - 1) >> bbits;
1740 
1741 	/*
1742 	 * Get all the dirty buffers mapped to disk addresses and
1743 	 * handle any aliases from the underlying blockdev's mapping.
1744 	 */
1745 	do {
1746 		if (block > last_block) {
1747 			/*
1748 			 * mapped buffers outside i_size will occur, because
1749 			 * this page can be outside i_size when there is a
1750 			 * truncate in progress.
1751 			 */
1752 			/*
1753 			 * The buffer was zeroed by block_write_full_page()
1754 			 */
1755 			clear_buffer_dirty(bh);
1756 			set_buffer_uptodate(bh);
1757 		} else if ((!buffer_mapped(bh) || buffer_delay(bh)) &&
1758 			   buffer_dirty(bh)) {
1759 			WARN_ON(bh->b_size != blocksize);
1760 			err = get_block(inode, block, bh, 1);
1761 			if (err)
1762 				goto recover;
1763 			clear_buffer_delay(bh);
1764 			if (buffer_new(bh)) {
1765 				/* blockdev mappings never come here */
1766 				clear_buffer_new(bh);
1767 				clean_bdev_bh_alias(bh);
1768 			}
1769 		}
1770 		bh = bh->b_this_page;
1771 		block++;
1772 	} while (bh != head);
1773 
1774 	do {
1775 		if (!buffer_mapped(bh))
1776 			continue;
1777 		/*
1778 		 * If it's a fully non-blocking write attempt and we cannot
1779 		 * lock the buffer then redirty the page.  Note that this can
1780 		 * potentially cause a busy-wait loop from writeback threads
1781 		 * and kswapd activity, but those code paths have their own
1782 		 * higher-level throttling.
1783 		 */
1784 		if (wbc->sync_mode != WB_SYNC_NONE) {
1785 			lock_buffer(bh);
1786 		} else if (!trylock_buffer(bh)) {
1787 			redirty_page_for_writepage(wbc, page);
1788 			continue;
1789 		}
1790 		if (test_clear_buffer_dirty(bh)) {
1791 			mark_buffer_async_write_endio(bh, handler);
1792 		} else {
1793 			unlock_buffer(bh);
1794 		}
1795 	} while ((bh = bh->b_this_page) != head);
1796 
1797 	/*
1798 	 * The page and its buffers are protected by PageWriteback(), so we can
1799 	 * drop the bh refcounts early.
1800 	 */
1801 	BUG_ON(PageWriteback(page));
1802 	set_page_writeback(page);
1803 
1804 	do {
1805 		struct buffer_head *next = bh->b_this_page;
1806 		if (buffer_async_write(bh)) {
1807 			submit_bh_wbc(REQ_OP_WRITE, write_flags, bh, wbc);
1808 			nr_underway++;
1809 		}
1810 		bh = next;
1811 	} while (bh != head);
1812 	unlock_page(page);
1813 
1814 	err = 0;
1815 done:
1816 	if (nr_underway == 0) {
1817 		/*
1818 		 * The page was marked dirty, but the buffers were
1819 		 * clean.  Someone wrote them back by hand with
1820 		 * ll_rw_block/submit_bh.  A rare case.
1821 		 */
1822 		end_page_writeback(page);
1823 
1824 		/*
1825 		 * The page and buffer_heads can be released at any time from
1826 		 * here on.
1827 		 */
1828 	}
1829 	return err;
1830 
1831 recover:
1832 	/*
1833 	 * ENOSPC, or some other error.  We may already have added some
1834 	 * blocks to the file, so we need to write these out to avoid
1835 	 * exposing stale data.
1836 	 * The page is currently locked and not marked for writeback
1837 	 */
1838 	bh = head;
1839 	/* Recovery: lock and submit the mapped buffers */
1840 	do {
1841 		if (buffer_mapped(bh) && buffer_dirty(bh) &&
1842 		    !buffer_delay(bh)) {
1843 			lock_buffer(bh);
1844 			mark_buffer_async_write_endio(bh, handler);
1845 		} else {
1846 			/*
1847 			 * The buffer may have been set dirty during
1848 			 * attachment to a dirty page.
1849 			 */
1850 			clear_buffer_dirty(bh);
1851 		}
1852 	} while ((bh = bh->b_this_page) != head);
1853 	SetPageError(page);
1854 	BUG_ON(PageWriteback(page));
1855 	mapping_set_error(page->mapping, err);
1856 	set_page_writeback(page);
1857 	do {
1858 		struct buffer_head *next = bh->b_this_page;
1859 		if (buffer_async_write(bh)) {
1860 			clear_buffer_dirty(bh);
1861 			submit_bh_wbc(REQ_OP_WRITE, write_flags, bh, wbc);
1862 			nr_underway++;
1863 		}
1864 		bh = next;
1865 	} while (bh != head);
1866 	unlock_page(page);
1867 	goto done;
1868 }
1869 EXPORT_SYMBOL(__block_write_full_page);
1870 
1871 /*
1872  * If a page has any new buffers, zero them out here, and mark them uptodate
1873  * and dirty so they'll be written out (in order to prevent uninitialised
1874  * block data from leaking). And clear the new bit.
1875  */
page_zero_new_buffers(struct page * page,unsigned from,unsigned to)1876 void page_zero_new_buffers(struct page *page, unsigned from, unsigned to)
1877 {
1878 	unsigned int block_start, block_end;
1879 	struct buffer_head *head, *bh;
1880 
1881 	BUG_ON(!PageLocked(page));
1882 	if (!page_has_buffers(page))
1883 		return;
1884 
1885 	bh = head = page_buffers(page);
1886 	block_start = 0;
1887 	do {
1888 		block_end = block_start + bh->b_size;
1889 
1890 		if (buffer_new(bh)) {
1891 			if (block_end > from && block_start < to) {
1892 				if (!PageUptodate(page)) {
1893 					unsigned start, size;
1894 
1895 					start = max(from, block_start);
1896 					size = min(to, block_end) - start;
1897 
1898 					zero_user(page, start, size);
1899 					set_buffer_uptodate(bh);
1900 				}
1901 
1902 				clear_buffer_new(bh);
1903 				mark_buffer_dirty(bh);
1904 			}
1905 		}
1906 
1907 		block_start = block_end;
1908 		bh = bh->b_this_page;
1909 	} while (bh != head);
1910 }
1911 EXPORT_SYMBOL(page_zero_new_buffers);
1912 
1913 static void
iomap_to_bh(struct inode * inode,sector_t block,struct buffer_head * bh,const struct iomap * iomap)1914 iomap_to_bh(struct inode *inode, sector_t block, struct buffer_head *bh,
1915 		const struct iomap *iomap)
1916 {
1917 	loff_t offset = block << inode->i_blkbits;
1918 
1919 	bh->b_bdev = iomap->bdev;
1920 
1921 	/*
1922 	 * Block points to offset in file we need to map, iomap contains
1923 	 * the offset at which the map starts. If the map ends before the
1924 	 * current block, then do not map the buffer and let the caller
1925 	 * handle it.
1926 	 */
1927 	BUG_ON(offset >= iomap->offset + iomap->length);
1928 
1929 	switch (iomap->type) {
1930 	case IOMAP_HOLE:
1931 		/*
1932 		 * If the buffer is not up to date or beyond the current EOF,
1933 		 * we need to mark it as new to ensure sub-block zeroing is
1934 		 * executed if necessary.
1935 		 */
1936 		if (!buffer_uptodate(bh) ||
1937 		    (offset >= i_size_read(inode)))
1938 			set_buffer_new(bh);
1939 		break;
1940 	case IOMAP_DELALLOC:
1941 		if (!buffer_uptodate(bh) ||
1942 		    (offset >= i_size_read(inode)))
1943 			set_buffer_new(bh);
1944 		set_buffer_uptodate(bh);
1945 		set_buffer_mapped(bh);
1946 		set_buffer_delay(bh);
1947 		break;
1948 	case IOMAP_UNWRITTEN:
1949 		/*
1950 		 * For unwritten regions, we always need to ensure that regions
1951 		 * in the block we are not writing to are zeroed. Mark the
1952 		 * buffer as new to ensure this.
1953 		 */
1954 		set_buffer_new(bh);
1955 		set_buffer_unwritten(bh);
1956 		fallthrough;
1957 	case IOMAP_MAPPED:
1958 		if ((iomap->flags & IOMAP_F_NEW) ||
1959 		    offset >= i_size_read(inode))
1960 			set_buffer_new(bh);
1961 		bh->b_blocknr = (iomap->addr + offset - iomap->offset) >>
1962 				inode->i_blkbits;
1963 		set_buffer_mapped(bh);
1964 		break;
1965 	}
1966 }
1967 
__block_write_begin_int(struct folio * folio,loff_t pos,unsigned len,get_block_t * get_block,const struct iomap * iomap)1968 int __block_write_begin_int(struct folio *folio, loff_t pos, unsigned len,
1969 		get_block_t *get_block, const struct iomap *iomap)
1970 {
1971 	unsigned from = pos & (PAGE_SIZE - 1);
1972 	unsigned to = from + len;
1973 	struct inode *inode = folio->mapping->host;
1974 	unsigned block_start, block_end;
1975 	sector_t block;
1976 	int err = 0;
1977 	unsigned blocksize, bbits;
1978 	struct buffer_head *bh, *head, *wait[2], **wait_bh=wait;
1979 
1980 	BUG_ON(!folio_test_locked(folio));
1981 	BUG_ON(from > PAGE_SIZE);
1982 	BUG_ON(to > PAGE_SIZE);
1983 	BUG_ON(from > to);
1984 
1985 	head = create_page_buffers(&folio->page, inode, 0);
1986 	blocksize = head->b_size;
1987 	bbits = block_size_bits(blocksize);
1988 
1989 	block = (sector_t)folio->index << (PAGE_SHIFT - bbits);
1990 
1991 	for(bh = head, block_start = 0; bh != head || !block_start;
1992 	    block++, block_start=block_end, bh = bh->b_this_page) {
1993 		block_end = block_start + blocksize;
1994 		if (block_end <= from || block_start >= to) {
1995 			if (folio_test_uptodate(folio)) {
1996 				if (!buffer_uptodate(bh))
1997 					set_buffer_uptodate(bh);
1998 			}
1999 			continue;
2000 		}
2001 		if (buffer_new(bh))
2002 			clear_buffer_new(bh);
2003 		if (!buffer_mapped(bh)) {
2004 			WARN_ON(bh->b_size != blocksize);
2005 			if (get_block) {
2006 				err = get_block(inode, block, bh, 1);
2007 				if (err)
2008 					break;
2009 			} else {
2010 				iomap_to_bh(inode, block, bh, iomap);
2011 			}
2012 
2013 			if (buffer_new(bh)) {
2014 				clean_bdev_bh_alias(bh);
2015 				if (folio_test_uptodate(folio)) {
2016 					clear_buffer_new(bh);
2017 					set_buffer_uptodate(bh);
2018 					mark_buffer_dirty(bh);
2019 					continue;
2020 				}
2021 				if (block_end > to || block_start < from)
2022 					folio_zero_segments(folio,
2023 						to, block_end,
2024 						block_start, from);
2025 				continue;
2026 			}
2027 		}
2028 		if (folio_test_uptodate(folio)) {
2029 			if (!buffer_uptodate(bh))
2030 				set_buffer_uptodate(bh);
2031 			continue;
2032 		}
2033 		if (!buffer_uptodate(bh) && !buffer_delay(bh) &&
2034 		    !buffer_unwritten(bh) &&
2035 		     (block_start < from || block_end > to)) {
2036 			ll_rw_block(REQ_OP_READ, 0, 1, &bh);
2037 			*wait_bh++=bh;
2038 		}
2039 	}
2040 	/*
2041 	 * If we issued read requests - let them complete.
2042 	 */
2043 	while(wait_bh > wait) {
2044 		wait_on_buffer(*--wait_bh);
2045 		if (!buffer_uptodate(*wait_bh))
2046 			err = -EIO;
2047 	}
2048 	if (unlikely(err))
2049 		page_zero_new_buffers(&folio->page, from, to);
2050 	return err;
2051 }
2052 
__block_write_begin(struct page * page,loff_t pos,unsigned len,get_block_t * get_block)2053 int __block_write_begin(struct page *page, loff_t pos, unsigned len,
2054 		get_block_t *get_block)
2055 {
2056 	return __block_write_begin_int(page_folio(page), pos, len, get_block,
2057 				       NULL);
2058 }
2059 EXPORT_SYMBOL(__block_write_begin);
2060 
__block_commit_write(struct inode * inode,struct page * page,unsigned from,unsigned to)2061 static int __block_commit_write(struct inode *inode, struct page *page,
2062 		unsigned from, unsigned to)
2063 {
2064 	unsigned block_start, block_end;
2065 	int partial = 0;
2066 	unsigned blocksize;
2067 	struct buffer_head *bh, *head;
2068 
2069 	bh = head = page_buffers(page);
2070 	blocksize = bh->b_size;
2071 
2072 	block_start = 0;
2073 	do {
2074 		block_end = block_start + blocksize;
2075 		if (block_end <= from || block_start >= to) {
2076 			if (!buffer_uptodate(bh))
2077 				partial = 1;
2078 		} else {
2079 			set_buffer_uptodate(bh);
2080 			mark_buffer_dirty(bh);
2081 		}
2082 		if (buffer_new(bh))
2083 			clear_buffer_new(bh);
2084 
2085 		block_start = block_end;
2086 		bh = bh->b_this_page;
2087 	} while (bh != head);
2088 
2089 	/*
2090 	 * If this is a partial write which happened to make all buffers
2091 	 * uptodate then we can optimize away a bogus read_folio() for
2092 	 * the next read(). Here we 'discover' whether the page went
2093 	 * uptodate as a result of this (potentially partial) write.
2094 	 */
2095 	if (!partial)
2096 		SetPageUptodate(page);
2097 	return 0;
2098 }
2099 
2100 /*
2101  * block_write_begin takes care of the basic task of block allocation and
2102  * bringing partial write blocks uptodate first.
2103  *
2104  * The filesystem needs to handle block truncation upon failure.
2105  */
block_write_begin(struct address_space * mapping,loff_t pos,unsigned len,struct page ** pagep,get_block_t * get_block)2106 int block_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
2107 		struct page **pagep, get_block_t *get_block)
2108 {
2109 	pgoff_t index = pos >> PAGE_SHIFT;
2110 	struct page *page;
2111 	int status;
2112 
2113 	page = grab_cache_page_write_begin(mapping, index);
2114 	if (!page)
2115 		return -ENOMEM;
2116 
2117 	status = __block_write_begin(page, pos, len, get_block);
2118 	if (unlikely(status)) {
2119 		unlock_page(page);
2120 		put_page(page);
2121 		page = NULL;
2122 	}
2123 
2124 	*pagep = page;
2125 	return status;
2126 }
2127 EXPORT_SYMBOL(block_write_begin);
2128 
block_write_end(struct file * file,struct address_space * mapping,loff_t pos,unsigned len,unsigned copied,struct page * page,void * fsdata)2129 int block_write_end(struct file *file, struct address_space *mapping,
2130 			loff_t pos, unsigned len, unsigned copied,
2131 			struct page *page, void *fsdata)
2132 {
2133 	struct inode *inode = mapping->host;
2134 	unsigned start;
2135 
2136 	start = pos & (PAGE_SIZE - 1);
2137 
2138 	if (unlikely(copied < len)) {
2139 		/*
2140 		 * The buffers that were written will now be uptodate, so
2141 		 * we don't have to worry about a read_folio reading them
2142 		 * and overwriting a partial write. However if we have
2143 		 * encountered a short write and only partially written
2144 		 * into a buffer, it will not be marked uptodate, so a
2145 		 * read_folio might come in and destroy our partial write.
2146 		 *
2147 		 * Do the simplest thing, and just treat any short write to a
2148 		 * non uptodate page as a zero-length write, and force the
2149 		 * caller to redo the whole thing.
2150 		 */
2151 		if (!PageUptodate(page))
2152 			copied = 0;
2153 
2154 		page_zero_new_buffers(page, start+copied, start+len);
2155 	}
2156 	flush_dcache_page(page);
2157 
2158 	/* This could be a short (even 0-length) commit */
2159 	__block_commit_write(inode, page, start, start+copied);
2160 
2161 	return copied;
2162 }
2163 EXPORT_SYMBOL(block_write_end);
2164 
generic_write_end(struct file * file,struct address_space * mapping,loff_t pos,unsigned len,unsigned copied,struct page * page,void * fsdata)2165 int generic_write_end(struct file *file, struct address_space *mapping,
2166 			loff_t pos, unsigned len, unsigned copied,
2167 			struct page *page, void *fsdata)
2168 {
2169 	struct inode *inode = mapping->host;
2170 	loff_t old_size = inode->i_size;
2171 	bool i_size_changed = false;
2172 
2173 	copied = block_write_end(file, mapping, pos, len, copied, page, fsdata);
2174 
2175 	/*
2176 	 * No need to use i_size_read() here, the i_size cannot change under us
2177 	 * because we hold i_rwsem.
2178 	 *
2179 	 * But it's important to update i_size while still holding page lock:
2180 	 * page writeout could otherwise come in and zero beyond i_size.
2181 	 */
2182 	if (pos + copied > inode->i_size) {
2183 		i_size_write(inode, pos + copied);
2184 		i_size_changed = true;
2185 	}
2186 
2187 	unlock_page(page);
2188 	put_page(page);
2189 
2190 	if (old_size < pos)
2191 		pagecache_isize_extended(inode, old_size, pos);
2192 	/*
2193 	 * Don't mark the inode dirty under page lock. First, it unnecessarily
2194 	 * makes the holding time of page lock longer. Second, it forces lock
2195 	 * ordering of page lock and transaction start for journaling
2196 	 * filesystems.
2197 	 */
2198 	if (i_size_changed)
2199 		mark_inode_dirty(inode);
2200 	return copied;
2201 }
2202 EXPORT_SYMBOL(generic_write_end);
2203 
2204 /*
2205  * block_is_partially_uptodate checks whether buffers within a folio are
2206  * uptodate or not.
2207  *
2208  * Returns true if all buffers which correspond to the specified part
2209  * of the folio are uptodate.
2210  */
block_is_partially_uptodate(struct folio * folio,size_t from,size_t count)2211 bool block_is_partially_uptodate(struct folio *folio, size_t from, size_t count)
2212 {
2213 	unsigned block_start, block_end, blocksize;
2214 	unsigned to;
2215 	struct buffer_head *bh, *head;
2216 	bool ret = true;
2217 
2218 	head = folio_buffers(folio);
2219 	if (!head)
2220 		return false;
2221 	blocksize = head->b_size;
2222 	to = min_t(unsigned, folio_size(folio) - from, count);
2223 	to = from + to;
2224 	if (from < blocksize && to > folio_size(folio) - blocksize)
2225 		return false;
2226 
2227 	bh = head;
2228 	block_start = 0;
2229 	do {
2230 		block_end = block_start + blocksize;
2231 		if (block_end > from && block_start < to) {
2232 			if (!buffer_uptodate(bh)) {
2233 				ret = false;
2234 				break;
2235 			}
2236 			if (block_end >= to)
2237 				break;
2238 		}
2239 		block_start = block_end;
2240 		bh = bh->b_this_page;
2241 	} while (bh != head);
2242 
2243 	return ret;
2244 }
2245 EXPORT_SYMBOL(block_is_partially_uptodate);
2246 
2247 /*
2248  * Generic "read_folio" function for block devices that have the normal
2249  * get_block functionality. This is most of the block device filesystems.
2250  * Reads the folio asynchronously --- the unlock_buffer() and
2251  * set/clear_buffer_uptodate() functions propagate buffer state into the
2252  * folio once IO has completed.
2253  */
block_read_full_folio(struct folio * folio,get_block_t * get_block)2254 int block_read_full_folio(struct folio *folio, get_block_t *get_block)
2255 {
2256 	struct inode *inode = folio->mapping->host;
2257 	sector_t iblock, lblock;
2258 	struct buffer_head *bh, *head, *arr[MAX_BUF_PER_PAGE];
2259 	unsigned int blocksize, bbits;
2260 	int nr, i;
2261 	int fully_mapped = 1;
2262 
2263 	VM_BUG_ON_FOLIO(folio_test_large(folio), folio);
2264 
2265 	head = create_page_buffers(&folio->page, inode, 0);
2266 	blocksize = head->b_size;
2267 	bbits = block_size_bits(blocksize);
2268 
2269 	iblock = (sector_t)folio->index << (PAGE_SHIFT - bbits);
2270 	lblock = (i_size_read(inode)+blocksize-1) >> bbits;
2271 	bh = head;
2272 	nr = 0;
2273 	i = 0;
2274 
2275 	do {
2276 		if (buffer_uptodate(bh))
2277 			continue;
2278 
2279 		if (!buffer_mapped(bh)) {
2280 			int err = 0;
2281 
2282 			fully_mapped = 0;
2283 			if (iblock < lblock) {
2284 				WARN_ON(bh->b_size != blocksize);
2285 				err = get_block(inode, iblock, bh, 0);
2286 				if (err)
2287 					folio_set_error(folio);
2288 			}
2289 			if (!buffer_mapped(bh)) {
2290 				folio_zero_range(folio, i * blocksize,
2291 						blocksize);
2292 				if (!err)
2293 					set_buffer_uptodate(bh);
2294 				continue;
2295 			}
2296 			/*
2297 			 * get_block() might have updated the buffer
2298 			 * synchronously
2299 			 */
2300 			if (buffer_uptodate(bh))
2301 				continue;
2302 		}
2303 		arr[nr++] = bh;
2304 	} while (i++, iblock++, (bh = bh->b_this_page) != head);
2305 
2306 	if (fully_mapped)
2307 		folio_set_mappedtodisk(folio);
2308 
2309 	if (!nr) {
2310 		/*
2311 		 * All buffers are uptodate - we can set the folio uptodate
2312 		 * as well. But not if get_block() returned an error.
2313 		 */
2314 		if (!folio_test_error(folio))
2315 			folio_mark_uptodate(folio);
2316 		folio_unlock(folio);
2317 		return 0;
2318 	}
2319 
2320 	/* Stage two: lock the buffers */
2321 	for (i = 0; i < nr; i++) {
2322 		bh = arr[i];
2323 		lock_buffer(bh);
2324 		mark_buffer_async_read(bh);
2325 	}
2326 
2327 	/*
2328 	 * Stage 3: start the IO.  Check for uptodateness
2329 	 * inside the buffer lock in case another process reading
2330 	 * the underlying blockdev brought it uptodate (the sct fix).
2331 	 */
2332 	for (i = 0; i < nr; i++) {
2333 		bh = arr[i];
2334 		if (buffer_uptodate(bh))
2335 			end_buffer_async_read(bh, 1);
2336 		else
2337 			submit_bh(REQ_OP_READ, 0, bh);
2338 	}
2339 	return 0;
2340 }
2341 EXPORT_SYMBOL(block_read_full_folio);
2342 
2343 /* utility function for filesystems that need to do work on expanding
2344  * truncates.  Uses filesystem pagecache writes to allow the filesystem to
2345  * deal with the hole.
2346  */
generic_cont_expand_simple(struct inode * inode,loff_t size)2347 int generic_cont_expand_simple(struct inode *inode, loff_t size)
2348 {
2349 	struct address_space *mapping = inode->i_mapping;
2350 	const struct address_space_operations *aops = mapping->a_ops;
2351 	struct page *page;
2352 	void *fsdata;
2353 	int err;
2354 
2355 	err = inode_newsize_ok(inode, size);
2356 	if (err)
2357 		goto out;
2358 
2359 	err = aops->write_begin(NULL, mapping, size, 0, &page, &fsdata);
2360 	if (err)
2361 		goto out;
2362 
2363 	err = aops->write_end(NULL, mapping, size, 0, 0, page, fsdata);
2364 	BUG_ON(err > 0);
2365 
2366 out:
2367 	return err;
2368 }
2369 EXPORT_SYMBOL(generic_cont_expand_simple);
2370 
cont_expand_zero(struct file * file,struct address_space * mapping,loff_t pos,loff_t * bytes)2371 static int cont_expand_zero(struct file *file, struct address_space *mapping,
2372 			    loff_t pos, loff_t *bytes)
2373 {
2374 	struct inode *inode = mapping->host;
2375 	const struct address_space_operations *aops = mapping->a_ops;
2376 	unsigned int blocksize = i_blocksize(inode);
2377 	struct page *page;
2378 	void *fsdata;
2379 	pgoff_t index, curidx;
2380 	loff_t curpos;
2381 	unsigned zerofrom, offset, len;
2382 	int err = 0;
2383 
2384 	index = pos >> PAGE_SHIFT;
2385 	offset = pos & ~PAGE_MASK;
2386 
2387 	while (index > (curidx = (curpos = *bytes)>>PAGE_SHIFT)) {
2388 		zerofrom = curpos & ~PAGE_MASK;
2389 		if (zerofrom & (blocksize-1)) {
2390 			*bytes |= (blocksize-1);
2391 			(*bytes)++;
2392 		}
2393 		len = PAGE_SIZE - zerofrom;
2394 
2395 		err = aops->write_begin(file, mapping, curpos, len,
2396 					    &page, &fsdata);
2397 		if (err)
2398 			goto out;
2399 		zero_user(page, zerofrom, len);
2400 		err = aops->write_end(file, mapping, curpos, len, len,
2401 						page, fsdata);
2402 		if (err < 0)
2403 			goto out;
2404 		BUG_ON(err != len);
2405 		err = 0;
2406 
2407 		balance_dirty_pages_ratelimited(mapping);
2408 
2409 		if (fatal_signal_pending(current)) {
2410 			err = -EINTR;
2411 			goto out;
2412 		}
2413 	}
2414 
2415 	/* page covers the boundary, find the boundary offset */
2416 	if (index == curidx) {
2417 		zerofrom = curpos & ~PAGE_MASK;
2418 		/* if we will expand the thing last block will be filled */
2419 		if (offset <= zerofrom) {
2420 			goto out;
2421 		}
2422 		if (zerofrom & (blocksize-1)) {
2423 			*bytes |= (blocksize-1);
2424 			(*bytes)++;
2425 		}
2426 		len = offset - zerofrom;
2427 
2428 		err = aops->write_begin(file, mapping, curpos, len,
2429 					    &page, &fsdata);
2430 		if (err)
2431 			goto out;
2432 		zero_user(page, zerofrom, len);
2433 		err = aops->write_end(file, mapping, curpos, len, len,
2434 						page, fsdata);
2435 		if (err < 0)
2436 			goto out;
2437 		BUG_ON(err != len);
2438 		err = 0;
2439 	}
2440 out:
2441 	return err;
2442 }
2443 
2444 /*
2445  * For moronic filesystems that do not allow holes in file.
2446  * We may have to extend the file.
2447  */
cont_write_begin(struct file * file,struct address_space * mapping,loff_t pos,unsigned len,struct page ** pagep,void ** fsdata,get_block_t * get_block,loff_t * bytes)2448 int cont_write_begin(struct file *file, struct address_space *mapping,
2449 			loff_t pos, unsigned len,
2450 			struct page **pagep, void **fsdata,
2451 			get_block_t *get_block, loff_t *bytes)
2452 {
2453 	struct inode *inode = mapping->host;
2454 	unsigned int blocksize = i_blocksize(inode);
2455 	unsigned int zerofrom;
2456 	int err;
2457 
2458 	err = cont_expand_zero(file, mapping, pos, bytes);
2459 	if (err)
2460 		return err;
2461 
2462 	zerofrom = *bytes & ~PAGE_MASK;
2463 	if (pos+len > *bytes && zerofrom & (blocksize-1)) {
2464 		*bytes |= (blocksize-1);
2465 		(*bytes)++;
2466 	}
2467 
2468 	return block_write_begin(mapping, pos, len, pagep, get_block);
2469 }
2470 EXPORT_SYMBOL(cont_write_begin);
2471 
block_commit_write(struct page * page,unsigned from,unsigned to)2472 int block_commit_write(struct page *page, unsigned from, unsigned to)
2473 {
2474 	struct inode *inode = page->mapping->host;
2475 	__block_commit_write(inode,page,from,to);
2476 	return 0;
2477 }
2478 EXPORT_SYMBOL(block_commit_write);
2479 
2480 /*
2481  * block_page_mkwrite() is not allowed to change the file size as it gets
2482  * called from a page fault handler when a page is first dirtied. Hence we must
2483  * be careful to check for EOF conditions here. We set the page up correctly
2484  * for a written page which means we get ENOSPC checking when writing into
2485  * holes and correct delalloc and unwritten extent mapping on filesystems that
2486  * support these features.
2487  *
2488  * We are not allowed to take the i_mutex here so we have to play games to
2489  * protect against truncate races as the page could now be beyond EOF.  Because
2490  * truncate writes the inode size before removing pages, once we have the
2491  * page lock we can determine safely if the page is beyond EOF. If it is not
2492  * beyond EOF, then the page is guaranteed safe against truncation until we
2493  * unlock the page.
2494  *
2495  * Direct callers of this function should protect against filesystem freezing
2496  * using sb_start_pagefault() - sb_end_pagefault() functions.
2497  */
block_page_mkwrite(struct vm_area_struct * vma,struct vm_fault * vmf,get_block_t get_block)2498 int block_page_mkwrite(struct vm_area_struct *vma, struct vm_fault *vmf,
2499 			 get_block_t get_block)
2500 {
2501 	struct page *page = vmf->page;
2502 	struct inode *inode = file_inode(vma->vm_file);
2503 	unsigned long end;
2504 	loff_t size;
2505 	int ret;
2506 
2507 	lock_page(page);
2508 	size = i_size_read(inode);
2509 	if ((page->mapping != inode->i_mapping) ||
2510 	    (page_offset(page) > size)) {
2511 		/* We overload EFAULT to mean page got truncated */
2512 		ret = -EFAULT;
2513 		goto out_unlock;
2514 	}
2515 
2516 	/* page is wholly or partially inside EOF */
2517 	if (((page->index + 1) << PAGE_SHIFT) > size)
2518 		end = size & ~PAGE_MASK;
2519 	else
2520 		end = PAGE_SIZE;
2521 
2522 	ret = __block_write_begin(page, 0, end, get_block);
2523 	if (!ret)
2524 		ret = block_commit_write(page, 0, end);
2525 
2526 	if (unlikely(ret < 0))
2527 		goto out_unlock;
2528 	set_page_dirty(page);
2529 	wait_for_stable_page(page);
2530 	return 0;
2531 out_unlock:
2532 	unlock_page(page);
2533 	return ret;
2534 }
2535 EXPORT_SYMBOL(block_page_mkwrite);
2536 
2537 /*
2538  * nobh_write_begin()'s prereads are special: the buffer_heads are freed
2539  * immediately, while under the page lock.  So it needs a special end_io
2540  * handler which does not touch the bh after unlocking it.
2541  */
end_buffer_read_nobh(struct buffer_head * bh,int uptodate)2542 static void end_buffer_read_nobh(struct buffer_head *bh, int uptodate)
2543 {
2544 	__end_buffer_read_notouch(bh, uptodate);
2545 }
2546 
2547 /*
2548  * Attach the singly-linked list of buffers created by nobh_write_begin, to
2549  * the page (converting it to circular linked list and taking care of page
2550  * dirty races).
2551  */
attach_nobh_buffers(struct page * page,struct buffer_head * head)2552 static void attach_nobh_buffers(struct page *page, struct buffer_head *head)
2553 {
2554 	struct buffer_head *bh;
2555 
2556 	BUG_ON(!PageLocked(page));
2557 
2558 	spin_lock(&page->mapping->private_lock);
2559 	bh = head;
2560 	do {
2561 		if (PageDirty(page))
2562 			set_buffer_dirty(bh);
2563 		if (!bh->b_this_page)
2564 			bh->b_this_page = head;
2565 		bh = bh->b_this_page;
2566 	} while (bh != head);
2567 	attach_page_private(page, head);
2568 	spin_unlock(&page->mapping->private_lock);
2569 }
2570 
2571 /*
2572  * On entry, the page is fully not uptodate.
2573  * On exit the page is fully uptodate in the areas outside (from,to)
2574  * The filesystem needs to handle block truncation upon failure.
2575  */
nobh_write_begin(struct address_space * mapping,loff_t pos,unsigned len,struct page ** pagep,void ** fsdata,get_block_t * get_block)2576 int nobh_write_begin(struct address_space *mapping, loff_t pos, unsigned len,
2577 			struct page **pagep, void **fsdata,
2578 			get_block_t *get_block)
2579 {
2580 	struct inode *inode = mapping->host;
2581 	const unsigned blkbits = inode->i_blkbits;
2582 	const unsigned blocksize = 1 << blkbits;
2583 	struct buffer_head *head, *bh;
2584 	struct page *page;
2585 	pgoff_t index;
2586 	unsigned from, to;
2587 	unsigned block_in_page;
2588 	unsigned block_start, block_end;
2589 	sector_t block_in_file;
2590 	int nr_reads = 0;
2591 	int ret = 0;
2592 	int is_mapped_to_disk = 1;
2593 
2594 	index = pos >> PAGE_SHIFT;
2595 	from = pos & (PAGE_SIZE - 1);
2596 	to = from + len;
2597 
2598 	page = grab_cache_page_write_begin(mapping, index);
2599 	if (!page)
2600 		return -ENOMEM;
2601 	*pagep = page;
2602 	*fsdata = NULL;
2603 
2604 	if (page_has_buffers(page)) {
2605 		ret = __block_write_begin(page, pos, len, get_block);
2606 		if (unlikely(ret))
2607 			goto out_release;
2608 		return ret;
2609 	}
2610 
2611 	if (PageMappedToDisk(page))
2612 		return 0;
2613 
2614 	/*
2615 	 * Allocate buffers so that we can keep track of state, and potentially
2616 	 * attach them to the page if an error occurs. In the common case of
2617 	 * no error, they will just be freed again without ever being attached
2618 	 * to the page (which is all OK, because we're under the page lock).
2619 	 *
2620 	 * Be careful: the buffer linked list is a NULL terminated one, rather
2621 	 * than the circular one we're used to.
2622 	 */
2623 	head = alloc_page_buffers(page, blocksize, false);
2624 	if (!head) {
2625 		ret = -ENOMEM;
2626 		goto out_release;
2627 	}
2628 
2629 	block_in_file = (sector_t)page->index << (PAGE_SHIFT - blkbits);
2630 
2631 	/*
2632 	 * We loop across all blocks in the page, whether or not they are
2633 	 * part of the affected region.  This is so we can discover if the
2634 	 * page is fully mapped-to-disk.
2635 	 */
2636 	for (block_start = 0, block_in_page = 0, bh = head;
2637 		  block_start < PAGE_SIZE;
2638 		  block_in_page++, block_start += blocksize, bh = bh->b_this_page) {
2639 		int create;
2640 
2641 		block_end = block_start + blocksize;
2642 		bh->b_state = 0;
2643 		create = 1;
2644 		if (block_start >= to)
2645 			create = 0;
2646 		ret = get_block(inode, block_in_file + block_in_page,
2647 					bh, create);
2648 		if (ret)
2649 			goto failed;
2650 		if (!buffer_mapped(bh))
2651 			is_mapped_to_disk = 0;
2652 		if (buffer_new(bh))
2653 			clean_bdev_bh_alias(bh);
2654 		if (PageUptodate(page)) {
2655 			set_buffer_uptodate(bh);
2656 			continue;
2657 		}
2658 		if (buffer_new(bh) || !buffer_mapped(bh)) {
2659 			zero_user_segments(page, block_start, from,
2660 							to, block_end);
2661 			continue;
2662 		}
2663 		if (buffer_uptodate(bh))
2664 			continue;	/* reiserfs does this */
2665 		if (block_start < from || block_end > to) {
2666 			lock_buffer(bh);
2667 			bh->b_end_io = end_buffer_read_nobh;
2668 			submit_bh(REQ_OP_READ, 0, bh);
2669 			nr_reads++;
2670 		}
2671 	}
2672 
2673 	if (nr_reads) {
2674 		/*
2675 		 * The page is locked, so these buffers are protected from
2676 		 * any VM or truncate activity.  Hence we don't need to care
2677 		 * for the buffer_head refcounts.
2678 		 */
2679 		for (bh = head; bh; bh = bh->b_this_page) {
2680 			wait_on_buffer(bh);
2681 			if (!buffer_uptodate(bh))
2682 				ret = -EIO;
2683 		}
2684 		if (ret)
2685 			goto failed;
2686 	}
2687 
2688 	if (is_mapped_to_disk)
2689 		SetPageMappedToDisk(page);
2690 
2691 	*fsdata = head; /* to be released by nobh_write_end */
2692 
2693 	return 0;
2694 
2695 failed:
2696 	BUG_ON(!ret);
2697 	/*
2698 	 * Error recovery is a bit difficult. We need to zero out blocks that
2699 	 * were newly allocated, and dirty them to ensure they get written out.
2700 	 * Buffers need to be attached to the page at this point, otherwise
2701 	 * the handling of potential IO errors during writeout would be hard
2702 	 * (could try doing synchronous writeout, but what if that fails too?)
2703 	 */
2704 	attach_nobh_buffers(page, head);
2705 	page_zero_new_buffers(page, from, to);
2706 
2707 out_release:
2708 	unlock_page(page);
2709 	put_page(page);
2710 	*pagep = NULL;
2711 
2712 	return ret;
2713 }
2714 EXPORT_SYMBOL(nobh_write_begin);
2715 
nobh_write_end(struct file * file,struct address_space * mapping,loff_t pos,unsigned len,unsigned copied,struct page * page,void * fsdata)2716 int nobh_write_end(struct file *file, struct address_space *mapping,
2717 			loff_t pos, unsigned len, unsigned copied,
2718 			struct page *page, void *fsdata)
2719 {
2720 	struct inode *inode = page->mapping->host;
2721 	struct buffer_head *head = fsdata;
2722 	struct buffer_head *bh;
2723 	BUG_ON(fsdata != NULL && page_has_buffers(page));
2724 
2725 	if (unlikely(copied < len) && head)
2726 		attach_nobh_buffers(page, head);
2727 	if (page_has_buffers(page))
2728 		return generic_write_end(file, mapping, pos, len,
2729 					copied, page, fsdata);
2730 
2731 	SetPageUptodate(page);
2732 	set_page_dirty(page);
2733 	if (pos+copied > inode->i_size) {
2734 		i_size_write(inode, pos+copied);
2735 		mark_inode_dirty(inode);
2736 	}
2737 
2738 	unlock_page(page);
2739 	put_page(page);
2740 
2741 	while (head) {
2742 		bh = head;
2743 		head = head->b_this_page;
2744 		free_buffer_head(bh);
2745 	}
2746 
2747 	return copied;
2748 }
2749 EXPORT_SYMBOL(nobh_write_end);
2750 
2751 /*
2752  * nobh_writepage() - based on block_full_write_page() except
2753  * that it tries to operate without attaching bufferheads to
2754  * the page.
2755  */
nobh_writepage(struct page * page,get_block_t * get_block,struct writeback_control * wbc)2756 int nobh_writepage(struct page *page, get_block_t *get_block,
2757 			struct writeback_control *wbc)
2758 {
2759 	struct inode * const inode = page->mapping->host;
2760 	loff_t i_size = i_size_read(inode);
2761 	const pgoff_t end_index = i_size >> PAGE_SHIFT;
2762 	unsigned offset;
2763 	int ret;
2764 
2765 	/* Is the page fully inside i_size? */
2766 	if (page->index < end_index)
2767 		goto out;
2768 
2769 	/* Is the page fully outside i_size? (truncate in progress) */
2770 	offset = i_size & (PAGE_SIZE-1);
2771 	if (page->index >= end_index+1 || !offset) {
2772 		unlock_page(page);
2773 		return 0; /* don't care */
2774 	}
2775 
2776 	/*
2777 	 * The page straddles i_size.  It must be zeroed out on each and every
2778 	 * writepage invocation because it may be mmapped.  "A file is mapped
2779 	 * in multiples of the page size.  For a file that is not a multiple of
2780 	 * the  page size, the remaining memory is zeroed when mapped, and
2781 	 * writes to that region are not written out to the file."
2782 	 */
2783 	zero_user_segment(page, offset, PAGE_SIZE);
2784 out:
2785 	ret = mpage_writepage(page, get_block, wbc);
2786 	if (ret == -EAGAIN)
2787 		ret = __block_write_full_page(inode, page, get_block, wbc,
2788 					      end_buffer_async_write);
2789 	return ret;
2790 }
2791 EXPORT_SYMBOL(nobh_writepage);
2792 
nobh_truncate_page(struct address_space * mapping,loff_t from,get_block_t * get_block)2793 int nobh_truncate_page(struct address_space *mapping,
2794 			loff_t from, get_block_t *get_block)
2795 {
2796 	pgoff_t index = from >> PAGE_SHIFT;
2797 	struct inode *inode = mapping->host;
2798 	unsigned blocksize = i_blocksize(inode);
2799 	struct folio *folio;
2800 	struct buffer_head map_bh;
2801 	size_t offset;
2802 	sector_t iblock;
2803 	int err;
2804 
2805 	/* Block boundary? Nothing to do */
2806 	if (!(from & (blocksize - 1)))
2807 		return 0;
2808 
2809 	folio = __filemap_get_folio(mapping, index, FGP_LOCK | FGP_CREAT,
2810 			mapping_gfp_mask(mapping));
2811 	err = -ENOMEM;
2812 	if (!folio)
2813 		goto out;
2814 
2815 	if (folio_buffers(folio))
2816 		goto has_buffers;
2817 
2818 	iblock = from >> inode->i_blkbits;
2819 	map_bh.b_size = blocksize;
2820 	map_bh.b_state = 0;
2821 	err = get_block(inode, iblock, &map_bh, 0);
2822 	if (err)
2823 		goto unlock;
2824 	/* unmapped? It's a hole - nothing to do */
2825 	if (!buffer_mapped(&map_bh))
2826 		goto unlock;
2827 
2828 	/* Ok, it's mapped. Make sure it's up-to-date */
2829 	if (!folio_test_uptodate(folio)) {
2830 		err = mapping->a_ops->read_folio(NULL, folio);
2831 		if (err) {
2832 			folio_put(folio);
2833 			goto out;
2834 		}
2835 		folio_lock(folio);
2836 		if (!folio_test_uptodate(folio)) {
2837 			err = -EIO;
2838 			goto unlock;
2839 		}
2840 		if (folio_buffers(folio))
2841 			goto has_buffers;
2842 	}
2843 	offset = offset_in_folio(folio, from);
2844 	folio_zero_segment(folio, offset, round_up(offset, blocksize));
2845 	folio_mark_dirty(folio);
2846 	err = 0;
2847 
2848 unlock:
2849 	folio_unlock(folio);
2850 	folio_put(folio);
2851 out:
2852 	return err;
2853 
2854 has_buffers:
2855 	folio_unlock(folio);
2856 	folio_put(folio);
2857 	return block_truncate_page(mapping, from, get_block);
2858 }
2859 EXPORT_SYMBOL(nobh_truncate_page);
2860 
block_truncate_page(struct address_space * mapping,loff_t from,get_block_t * get_block)2861 int block_truncate_page(struct address_space *mapping,
2862 			loff_t from, get_block_t *get_block)
2863 {
2864 	pgoff_t index = from >> PAGE_SHIFT;
2865 	unsigned offset = from & (PAGE_SIZE-1);
2866 	unsigned blocksize;
2867 	sector_t iblock;
2868 	unsigned length, pos;
2869 	struct inode *inode = mapping->host;
2870 	struct page *page;
2871 	struct buffer_head *bh;
2872 	int err;
2873 
2874 	blocksize = i_blocksize(inode);
2875 	length = offset & (blocksize - 1);
2876 
2877 	/* Block boundary? Nothing to do */
2878 	if (!length)
2879 		return 0;
2880 
2881 	length = blocksize - length;
2882 	iblock = (sector_t)index << (PAGE_SHIFT - inode->i_blkbits);
2883 
2884 	page = grab_cache_page(mapping, index);
2885 	err = -ENOMEM;
2886 	if (!page)
2887 		goto out;
2888 
2889 	if (!page_has_buffers(page))
2890 		create_empty_buffers(page, blocksize, 0);
2891 
2892 	/* Find the buffer that contains "offset" */
2893 	bh = page_buffers(page);
2894 	pos = blocksize;
2895 	while (offset >= pos) {
2896 		bh = bh->b_this_page;
2897 		iblock++;
2898 		pos += blocksize;
2899 	}
2900 
2901 	err = 0;
2902 	if (!buffer_mapped(bh)) {
2903 		WARN_ON(bh->b_size != blocksize);
2904 		err = get_block(inode, iblock, bh, 0);
2905 		if (err)
2906 			goto unlock;
2907 		/* unmapped? It's a hole - nothing to do */
2908 		if (!buffer_mapped(bh))
2909 			goto unlock;
2910 	}
2911 
2912 	/* Ok, it's mapped. Make sure it's up-to-date */
2913 	if (PageUptodate(page))
2914 		set_buffer_uptodate(bh);
2915 
2916 	if (!buffer_uptodate(bh) && !buffer_delay(bh) && !buffer_unwritten(bh)) {
2917 		err = -EIO;
2918 		ll_rw_block(REQ_OP_READ, 0, 1, &bh);
2919 		wait_on_buffer(bh);
2920 		/* Uhhuh. Read error. Complain and punt. */
2921 		if (!buffer_uptodate(bh))
2922 			goto unlock;
2923 	}
2924 
2925 	zero_user(page, offset, length);
2926 	mark_buffer_dirty(bh);
2927 	err = 0;
2928 
2929 unlock:
2930 	unlock_page(page);
2931 	put_page(page);
2932 out:
2933 	return err;
2934 }
2935 EXPORT_SYMBOL(block_truncate_page);
2936 
2937 /*
2938  * The generic ->writepage function for buffer-backed address_spaces
2939  */
block_write_full_page(struct page * page,get_block_t * get_block,struct writeback_control * wbc)2940 int block_write_full_page(struct page *page, get_block_t *get_block,
2941 			struct writeback_control *wbc)
2942 {
2943 	struct inode * const inode = page->mapping->host;
2944 	loff_t i_size = i_size_read(inode);
2945 	const pgoff_t end_index = i_size >> PAGE_SHIFT;
2946 	unsigned offset;
2947 
2948 	/* Is the page fully inside i_size? */
2949 	if (page->index < end_index)
2950 		return __block_write_full_page(inode, page, get_block, wbc,
2951 					       end_buffer_async_write);
2952 
2953 	/* Is the page fully outside i_size? (truncate in progress) */
2954 	offset = i_size & (PAGE_SIZE-1);
2955 	if (page->index >= end_index+1 || !offset) {
2956 		unlock_page(page);
2957 		return 0; /* don't care */
2958 	}
2959 
2960 	/*
2961 	 * The page straddles i_size.  It must be zeroed out on each and every
2962 	 * writepage invocation because it may be mmapped.  "A file is mapped
2963 	 * in multiples of the page size.  For a file that is not a multiple of
2964 	 * the  page size, the remaining memory is zeroed when mapped, and
2965 	 * writes to that region are not written out to the file."
2966 	 */
2967 	zero_user_segment(page, offset, PAGE_SIZE);
2968 	return __block_write_full_page(inode, page, get_block, wbc,
2969 							end_buffer_async_write);
2970 }
2971 EXPORT_SYMBOL(block_write_full_page);
2972 
generic_block_bmap(struct address_space * mapping,sector_t block,get_block_t * get_block)2973 sector_t generic_block_bmap(struct address_space *mapping, sector_t block,
2974 			    get_block_t *get_block)
2975 {
2976 	struct inode *inode = mapping->host;
2977 	struct buffer_head tmp = {
2978 		.b_size = i_blocksize(inode),
2979 	};
2980 
2981 	get_block(inode, block, &tmp, 0);
2982 	return tmp.b_blocknr;
2983 }
2984 EXPORT_SYMBOL(generic_block_bmap);
2985 
end_bio_bh_io_sync(struct bio * bio)2986 static void end_bio_bh_io_sync(struct bio *bio)
2987 {
2988 	struct buffer_head *bh = bio->bi_private;
2989 
2990 	if (unlikely(bio_flagged(bio, BIO_QUIET)))
2991 		set_bit(BH_Quiet, &bh->b_state);
2992 
2993 	bh->b_end_io(bh, !bio->bi_status);
2994 	bio_put(bio);
2995 }
2996 
submit_bh_wbc(int op,int op_flags,struct buffer_head * bh,struct writeback_control * wbc)2997 static int submit_bh_wbc(int op, int op_flags, struct buffer_head *bh,
2998 			 struct writeback_control *wbc)
2999 {
3000 	struct bio *bio;
3001 
3002 	BUG_ON(!buffer_locked(bh));
3003 	BUG_ON(!buffer_mapped(bh));
3004 	BUG_ON(!bh->b_end_io);
3005 	BUG_ON(buffer_delay(bh));
3006 	BUG_ON(buffer_unwritten(bh));
3007 
3008 	/*
3009 	 * Only clear out a write error when rewriting
3010 	 */
3011 	if (test_set_buffer_req(bh) && (op == REQ_OP_WRITE))
3012 		clear_buffer_write_io_error(bh);
3013 
3014 	if (buffer_meta(bh))
3015 		op_flags |= REQ_META;
3016 	if (buffer_prio(bh))
3017 		op_flags |= REQ_PRIO;
3018 
3019 	bio = bio_alloc(bh->b_bdev, 1, op | op_flags, GFP_NOIO);
3020 
3021 	fscrypt_set_bio_crypt_ctx_bh(bio, bh, GFP_NOIO);
3022 
3023 	bio->bi_iter.bi_sector = bh->b_blocknr * (bh->b_size >> 9);
3024 
3025 	bio_add_page(bio, bh->b_page, bh->b_size, bh_offset(bh));
3026 	BUG_ON(bio->bi_iter.bi_size != bh->b_size);
3027 
3028 	bio->bi_end_io = end_bio_bh_io_sync;
3029 	bio->bi_private = bh;
3030 
3031 	/* Take care of bh's that straddle the end of the device */
3032 	guard_bio_eod(bio);
3033 
3034 	if (wbc) {
3035 		wbc_init_bio(wbc, bio);
3036 		wbc_account_cgroup_owner(wbc, bh->b_page, bh->b_size);
3037 	}
3038 
3039 	submit_bio(bio);
3040 	return 0;
3041 }
3042 
submit_bh(int op,int op_flags,struct buffer_head * bh)3043 int submit_bh(int op, int op_flags, struct buffer_head *bh)
3044 {
3045 	return submit_bh_wbc(op, op_flags, bh, NULL);
3046 }
3047 EXPORT_SYMBOL(submit_bh);
3048 
3049 /**
3050  * ll_rw_block: low-level access to block devices (DEPRECATED)
3051  * @op: whether to %READ or %WRITE
3052  * @op_flags: req_flag_bits
3053  * @nr: number of &struct buffer_heads in the array
3054  * @bhs: array of pointers to &struct buffer_head
3055  *
3056  * ll_rw_block() takes an array of pointers to &struct buffer_heads, and
3057  * requests an I/O operation on them, either a %REQ_OP_READ or a %REQ_OP_WRITE.
3058  * @op_flags contains flags modifying the detailed I/O behavior, most notably
3059  * %REQ_RAHEAD.
3060  *
3061  * This function drops any buffer that it cannot get a lock on (with the
3062  * BH_Lock state bit), any buffer that appears to be clean when doing a write
3063  * request, and any buffer that appears to be up-to-date when doing read
3064  * request.  Further it marks as clean buffers that are processed for
3065  * writing (the buffer cache won't assume that they are actually clean
3066  * until the buffer gets unlocked).
3067  *
3068  * ll_rw_block sets b_end_io to simple completion handler that marks
3069  * the buffer up-to-date (if appropriate), unlocks the buffer and wakes
3070  * any waiters.
3071  *
3072  * All of the buffers must be for the same device, and must also be a
3073  * multiple of the current approved size for the device.
3074  */
ll_rw_block(int op,int op_flags,int nr,struct buffer_head * bhs[])3075 void ll_rw_block(int op, int op_flags,  int nr, struct buffer_head *bhs[])
3076 {
3077 	int i;
3078 
3079 	for (i = 0; i < nr; i++) {
3080 		struct buffer_head *bh = bhs[i];
3081 
3082 		if (!trylock_buffer(bh))
3083 			continue;
3084 		if (op == WRITE) {
3085 			if (test_clear_buffer_dirty(bh)) {
3086 				bh->b_end_io = end_buffer_write_sync;
3087 				get_bh(bh);
3088 				submit_bh(op, op_flags, bh);
3089 				continue;
3090 			}
3091 		} else {
3092 			if (!buffer_uptodate(bh)) {
3093 				bh->b_end_io = end_buffer_read_sync;
3094 				get_bh(bh);
3095 				submit_bh(op, op_flags, bh);
3096 				continue;
3097 			}
3098 		}
3099 		unlock_buffer(bh);
3100 	}
3101 }
3102 EXPORT_SYMBOL(ll_rw_block);
3103 
write_dirty_buffer(struct buffer_head * bh,int op_flags)3104 void write_dirty_buffer(struct buffer_head *bh, int op_flags)
3105 {
3106 	lock_buffer(bh);
3107 	if (!test_clear_buffer_dirty(bh)) {
3108 		unlock_buffer(bh);
3109 		return;
3110 	}
3111 	bh->b_end_io = end_buffer_write_sync;
3112 	get_bh(bh);
3113 	submit_bh(REQ_OP_WRITE, op_flags, bh);
3114 }
3115 EXPORT_SYMBOL(write_dirty_buffer);
3116 
3117 /*
3118  * For a data-integrity writeout, we need to wait upon any in-progress I/O
3119  * and then start new I/O and then wait upon it.  The caller must have a ref on
3120  * the buffer_head.
3121  */
__sync_dirty_buffer(struct buffer_head * bh,int op_flags)3122 int __sync_dirty_buffer(struct buffer_head *bh, int op_flags)
3123 {
3124 	int ret = 0;
3125 
3126 	WARN_ON(atomic_read(&bh->b_count) < 1);
3127 	lock_buffer(bh);
3128 	if (test_clear_buffer_dirty(bh)) {
3129 		/*
3130 		 * The bh should be mapped, but it might not be if the
3131 		 * device was hot-removed. Not much we can do but fail the I/O.
3132 		 */
3133 		if (!buffer_mapped(bh)) {
3134 			unlock_buffer(bh);
3135 			return -EIO;
3136 		}
3137 
3138 		get_bh(bh);
3139 		bh->b_end_io = end_buffer_write_sync;
3140 		ret = submit_bh(REQ_OP_WRITE, op_flags, bh);
3141 		wait_on_buffer(bh);
3142 		if (!ret && !buffer_uptodate(bh))
3143 			ret = -EIO;
3144 	} else {
3145 		unlock_buffer(bh);
3146 	}
3147 	return ret;
3148 }
3149 EXPORT_SYMBOL(__sync_dirty_buffer);
3150 
sync_dirty_buffer(struct buffer_head * bh)3151 int sync_dirty_buffer(struct buffer_head *bh)
3152 {
3153 	return __sync_dirty_buffer(bh, REQ_SYNC);
3154 }
3155 EXPORT_SYMBOL(sync_dirty_buffer);
3156 
3157 /*
3158  * try_to_free_buffers() checks if all the buffers on this particular folio
3159  * are unused, and releases them if so.
3160  *
3161  * Exclusion against try_to_free_buffers may be obtained by either
3162  * locking the folio or by holding its mapping's private_lock.
3163  *
3164  * If the folio is dirty but all the buffers are clean then we need to
3165  * be sure to mark the folio clean as well.  This is because the folio
3166  * may be against a block device, and a later reattachment of buffers
3167  * to a dirty folio will set *all* buffers dirty.  Which would corrupt
3168  * filesystem data on the same device.
3169  *
3170  * The same applies to regular filesystem folios: if all the buffers are
3171  * clean then we set the folio clean and proceed.  To do that, we require
3172  * total exclusion from block_dirty_folio().  That is obtained with
3173  * private_lock.
3174  *
3175  * try_to_free_buffers() is non-blocking.
3176  */
buffer_busy(struct buffer_head * bh)3177 static inline int buffer_busy(struct buffer_head *bh)
3178 {
3179 	return atomic_read(&bh->b_count) |
3180 		(bh->b_state & ((1 << BH_Dirty) | (1 << BH_Lock)));
3181 }
3182 
3183 static bool
drop_buffers(struct folio * folio,struct buffer_head ** buffers_to_free)3184 drop_buffers(struct folio *folio, struct buffer_head **buffers_to_free)
3185 {
3186 	struct buffer_head *head = folio_buffers(folio);
3187 	struct buffer_head *bh;
3188 
3189 	bh = head;
3190 	do {
3191 		if (buffer_busy(bh))
3192 			goto failed;
3193 		bh = bh->b_this_page;
3194 	} while (bh != head);
3195 
3196 	do {
3197 		struct buffer_head *next = bh->b_this_page;
3198 
3199 		if (bh->b_assoc_map)
3200 			__remove_assoc_queue(bh);
3201 		bh = next;
3202 	} while (bh != head);
3203 	*buffers_to_free = head;
3204 	folio_detach_private(folio);
3205 	return true;
3206 failed:
3207 	return false;
3208 }
3209 
try_to_free_buffers(struct folio * folio)3210 bool try_to_free_buffers(struct folio *folio)
3211 {
3212 	struct address_space * const mapping = folio->mapping;
3213 	struct buffer_head *buffers_to_free = NULL;
3214 	bool ret = 0;
3215 
3216 	BUG_ON(!folio_test_locked(folio));
3217 	if (folio_test_writeback(folio))
3218 		return false;
3219 
3220 	if (mapping == NULL) {		/* can this still happen? */
3221 		ret = drop_buffers(folio, &buffers_to_free);
3222 		goto out;
3223 	}
3224 
3225 	spin_lock(&mapping->private_lock);
3226 	ret = drop_buffers(folio, &buffers_to_free);
3227 
3228 	/*
3229 	 * If the filesystem writes its buffers by hand (eg ext3)
3230 	 * then we can have clean buffers against a dirty folio.  We
3231 	 * clean the folio here; otherwise the VM will never notice
3232 	 * that the filesystem did any IO at all.
3233 	 *
3234 	 * Also, during truncate, discard_buffer will have marked all
3235 	 * the folio's buffers clean.  We discover that here and clean
3236 	 * the folio also.
3237 	 *
3238 	 * private_lock must be held over this entire operation in order
3239 	 * to synchronise against block_dirty_folio and prevent the
3240 	 * dirty bit from being lost.
3241 	 */
3242 	if (ret)
3243 		folio_cancel_dirty(folio);
3244 	spin_unlock(&mapping->private_lock);
3245 out:
3246 	if (buffers_to_free) {
3247 		struct buffer_head *bh = buffers_to_free;
3248 
3249 		do {
3250 			struct buffer_head *next = bh->b_this_page;
3251 			free_buffer_head(bh);
3252 			bh = next;
3253 		} while (bh != buffers_to_free);
3254 	}
3255 	return ret;
3256 }
3257 EXPORT_SYMBOL(try_to_free_buffers);
3258 
3259 /*
3260  * Buffer-head allocation
3261  */
3262 static struct kmem_cache *bh_cachep __read_mostly;
3263 
3264 /*
3265  * Once the number of bh's in the machine exceeds this level, we start
3266  * stripping them in writeback.
3267  */
3268 static unsigned long max_buffer_heads;
3269 
3270 int buffer_heads_over_limit;
3271 
3272 struct bh_accounting {
3273 	int nr;			/* Number of live bh's */
3274 	int ratelimit;		/* Limit cacheline bouncing */
3275 };
3276 
3277 static DEFINE_PER_CPU(struct bh_accounting, bh_accounting) = {0, 0};
3278 
recalc_bh_state(void)3279 static void recalc_bh_state(void)
3280 {
3281 	int i;
3282 	int tot = 0;
3283 
3284 	if (__this_cpu_inc_return(bh_accounting.ratelimit) - 1 < 4096)
3285 		return;
3286 	__this_cpu_write(bh_accounting.ratelimit, 0);
3287 	for_each_online_cpu(i)
3288 		tot += per_cpu(bh_accounting, i).nr;
3289 	buffer_heads_over_limit = (tot > max_buffer_heads);
3290 }
3291 
alloc_buffer_head(gfp_t gfp_flags)3292 struct buffer_head *alloc_buffer_head(gfp_t gfp_flags)
3293 {
3294 	struct buffer_head *ret = kmem_cache_zalloc(bh_cachep, gfp_flags);
3295 	if (ret) {
3296 		INIT_LIST_HEAD(&ret->b_assoc_buffers);
3297 		spin_lock_init(&ret->b_uptodate_lock);
3298 		preempt_disable();
3299 		__this_cpu_inc(bh_accounting.nr);
3300 		recalc_bh_state();
3301 		preempt_enable();
3302 	}
3303 	return ret;
3304 }
3305 EXPORT_SYMBOL(alloc_buffer_head);
3306 
free_buffer_head(struct buffer_head * bh)3307 void free_buffer_head(struct buffer_head *bh)
3308 {
3309 	BUG_ON(!list_empty(&bh->b_assoc_buffers));
3310 	kmem_cache_free(bh_cachep, bh);
3311 	preempt_disable();
3312 	__this_cpu_dec(bh_accounting.nr);
3313 	recalc_bh_state();
3314 	preempt_enable();
3315 }
3316 EXPORT_SYMBOL(free_buffer_head);
3317 
buffer_exit_cpu_dead(unsigned int cpu)3318 static int buffer_exit_cpu_dead(unsigned int cpu)
3319 {
3320 	int i;
3321 	struct bh_lru *b = &per_cpu(bh_lrus, cpu);
3322 
3323 	for (i = 0; i < BH_LRU_SIZE; i++) {
3324 		brelse(b->bhs[i]);
3325 		b->bhs[i] = NULL;
3326 	}
3327 	this_cpu_add(bh_accounting.nr, per_cpu(bh_accounting, cpu).nr);
3328 	per_cpu(bh_accounting, cpu).nr = 0;
3329 	return 0;
3330 }
3331 
3332 /**
3333  * bh_uptodate_or_lock - Test whether the buffer is uptodate
3334  * @bh: struct buffer_head
3335  *
3336  * Return true if the buffer is up-to-date and false,
3337  * with the buffer locked, if not.
3338  */
bh_uptodate_or_lock(struct buffer_head * bh)3339 int bh_uptodate_or_lock(struct buffer_head *bh)
3340 {
3341 	if (!buffer_uptodate(bh)) {
3342 		lock_buffer(bh);
3343 		if (!buffer_uptodate(bh))
3344 			return 0;
3345 		unlock_buffer(bh);
3346 	}
3347 	return 1;
3348 }
3349 EXPORT_SYMBOL(bh_uptodate_or_lock);
3350 
3351 /**
3352  * bh_submit_read - Submit a locked buffer for reading
3353  * @bh: struct buffer_head
3354  *
3355  * Returns zero on success and -EIO on error.
3356  */
bh_submit_read(struct buffer_head * bh)3357 int bh_submit_read(struct buffer_head *bh)
3358 {
3359 	BUG_ON(!buffer_locked(bh));
3360 
3361 	if (buffer_uptodate(bh)) {
3362 		unlock_buffer(bh);
3363 		return 0;
3364 	}
3365 
3366 	get_bh(bh);
3367 	bh->b_end_io = end_buffer_read_sync;
3368 	submit_bh(REQ_OP_READ, 0, bh);
3369 	wait_on_buffer(bh);
3370 	if (buffer_uptodate(bh))
3371 		return 0;
3372 	return -EIO;
3373 }
3374 EXPORT_SYMBOL(bh_submit_read);
3375 
buffer_init(void)3376 void __init buffer_init(void)
3377 {
3378 	unsigned long nrpages;
3379 	int ret;
3380 
3381 	bh_cachep = kmem_cache_create("buffer_head",
3382 			sizeof(struct buffer_head), 0,
3383 				(SLAB_RECLAIM_ACCOUNT|SLAB_PANIC|
3384 				SLAB_MEM_SPREAD),
3385 				NULL);
3386 
3387 	/*
3388 	 * Limit the bh occupancy to 10% of ZONE_NORMAL
3389 	 */
3390 	nrpages = (nr_free_buffer_pages() * 10) / 100;
3391 	max_buffer_heads = nrpages * (PAGE_SIZE / sizeof(struct buffer_head));
3392 	ret = cpuhp_setup_state_nocalls(CPUHP_FS_BUFF_DEAD, "fs/buffer:dead",
3393 					NULL, buffer_exit_cpu_dead);
3394 	WARN_ON(ret < 0);
3395 }
3396