1 // SPDX-License-Identifier: GPL-2.0-only
2 /*
3  * fs/fs-writeback.c
4  *
5  * Copyright (C) 2002, Linus Torvalds.
6  *
7  * Contains all the functions related to writing back and waiting
8  * upon dirty inodes against superblocks, and writing back dirty
9  * pages against inodes.  ie: data writeback.  Writeout of the
10  * inode itself is not handled here.
11  *
12  * 10Apr2002	Andrew Morton
13  *		Split out of fs/inode.c
14  *		Additions for address_space-based writeback
15  */
16 
17 #include <linux/kernel.h>
18 #include <linux/export.h>
19 #include <linux/spinlock.h>
20 #include <linux/slab.h>
21 #include <linux/sched.h>
22 #include <linux/fs.h>
23 #include <linux/mm.h>
24 #include <linux/pagemap.h>
25 #include <linux/kthread.h>
26 #include <linux/writeback.h>
27 #include <linux/blkdev.h>
28 #include <linux/backing-dev.h>
29 #include <linux/tracepoint.h>
30 #include <linux/device.h>
31 #include <linux/memcontrol.h>
32 #include "internal.h"
33 
34 /*
35  * 4MB minimal write chunk size
36  */
37 #define MIN_WRITEBACK_PAGES	(4096UL >> (PAGE_SHIFT - 10))
38 
39 /*
40  * Passed into wb_writeback(), essentially a subset of writeback_control
41  */
42 struct wb_writeback_work {
43 	long nr_pages;
44 	struct super_block *sb;
45 	enum writeback_sync_modes sync_mode;
46 	unsigned int tagged_writepages:1;
47 	unsigned int for_kupdate:1;
48 	unsigned int range_cyclic:1;
49 	unsigned int for_background:1;
50 	unsigned int for_sync:1;	/* sync(2) WB_SYNC_ALL writeback */
51 	unsigned int auto_free:1;	/* free on completion */
52 	enum wb_reason reason;		/* why was writeback initiated? */
53 
54 	struct list_head list;		/* pending work list */
55 	struct wb_completion *done;	/* set if the caller waits */
56 };
57 
58 /*
59  * If an inode is constantly having its pages dirtied, but then the
60  * updates stop dirtytime_expire_interval seconds in the past, it's
61  * possible for the worst case time between when an inode has its
62  * timestamps updated and when they finally get written out to be two
63  * dirtytime_expire_intervals.  We set the default to 12 hours (in
64  * seconds), which means most of the time inodes will have their
65  * timestamps written to disk after 12 hours, but in the worst case a
66  * few inodes might not their timestamps updated for 24 hours.
67  */
68 unsigned int dirtytime_expire_interval = 12 * 60 * 60;
69 
wb_inode(struct list_head * head)70 static inline struct inode *wb_inode(struct list_head *head)
71 {
72 	return list_entry(head, struct inode, i_io_list);
73 }
74 
75 /*
76  * Include the creation of the trace points after defining the
77  * wb_writeback_work structure and inline functions so that the definition
78  * remains local to this file.
79  */
80 #define CREATE_TRACE_POINTS
81 #include <trace/events/writeback.h>
82 
83 EXPORT_TRACEPOINT_SYMBOL_GPL(wbc_writepage);
84 
wb_io_lists_populated(struct bdi_writeback * wb)85 static bool wb_io_lists_populated(struct bdi_writeback *wb)
86 {
87 	if (wb_has_dirty_io(wb)) {
88 		return false;
89 	} else {
90 		set_bit(WB_has_dirty_io, &wb->state);
91 		WARN_ON_ONCE(!wb->avg_write_bandwidth);
92 		atomic_long_add(wb->avg_write_bandwidth,
93 				&wb->bdi->tot_write_bandwidth);
94 		return true;
95 	}
96 }
97 
wb_io_lists_depopulated(struct bdi_writeback * wb)98 static void wb_io_lists_depopulated(struct bdi_writeback *wb)
99 {
100 	if (wb_has_dirty_io(wb) && list_empty(&wb->b_dirty) &&
101 	    list_empty(&wb->b_io) && list_empty(&wb->b_more_io)) {
102 		clear_bit(WB_has_dirty_io, &wb->state);
103 		WARN_ON_ONCE(atomic_long_sub_return(wb->avg_write_bandwidth,
104 					&wb->bdi->tot_write_bandwidth) < 0);
105 	}
106 }
107 
108 /**
109  * inode_io_list_move_locked - move an inode onto a bdi_writeback IO list
110  * @inode: inode to be moved
111  * @wb: target bdi_writeback
112  * @head: one of @wb->b_{dirty|io|more_io|dirty_time}
113  *
114  * Move @inode->i_io_list to @list of @wb and set %WB_has_dirty_io.
115  * Returns %true if @inode is the first occupant of the !dirty_time IO
116  * lists; otherwise, %false.
117  */
inode_io_list_move_locked(struct inode * inode,struct bdi_writeback * wb,struct list_head * head)118 static bool inode_io_list_move_locked(struct inode *inode,
119 				      struct bdi_writeback *wb,
120 				      struct list_head *head)
121 {
122 	assert_spin_locked(&wb->list_lock);
123 	assert_spin_locked(&inode->i_lock);
124 
125 	list_move(&inode->i_io_list, head);
126 
127 	/* dirty_time doesn't count as dirty_io until expiration */
128 	if (head != &wb->b_dirty_time)
129 		return wb_io_lists_populated(wb);
130 
131 	wb_io_lists_depopulated(wb);
132 	return false;
133 }
134 
wb_wakeup(struct bdi_writeback * wb)135 static void wb_wakeup(struct bdi_writeback *wb)
136 {
137 	spin_lock_irq(&wb->work_lock);
138 	if (test_bit(WB_registered, &wb->state))
139 		mod_delayed_work(bdi_wq, &wb->dwork, 0);
140 	spin_unlock_irq(&wb->work_lock);
141 }
142 
finish_writeback_work(struct bdi_writeback * wb,struct wb_writeback_work * work)143 static void finish_writeback_work(struct bdi_writeback *wb,
144 				  struct wb_writeback_work *work)
145 {
146 	struct wb_completion *done = work->done;
147 
148 	if (work->auto_free)
149 		kfree(work);
150 	if (done) {
151 		wait_queue_head_t *waitq = done->waitq;
152 
153 		/* @done can't be accessed after the following dec */
154 		if (atomic_dec_and_test(&done->cnt))
155 			wake_up_all(waitq);
156 	}
157 }
158 
wb_queue_work(struct bdi_writeback * wb,struct wb_writeback_work * work)159 static void wb_queue_work(struct bdi_writeback *wb,
160 			  struct wb_writeback_work *work)
161 {
162 	trace_writeback_queue(wb, work);
163 
164 	if (work->done)
165 		atomic_inc(&work->done->cnt);
166 
167 	spin_lock_irq(&wb->work_lock);
168 
169 	if (test_bit(WB_registered, &wb->state)) {
170 		list_add_tail(&work->list, &wb->work_list);
171 		mod_delayed_work(bdi_wq, &wb->dwork, 0);
172 	} else
173 		finish_writeback_work(wb, work);
174 
175 	spin_unlock_irq(&wb->work_lock);
176 }
177 
178 /**
179  * wb_wait_for_completion - wait for completion of bdi_writeback_works
180  * @done: target wb_completion
181  *
182  * Wait for one or more work items issued to @bdi with their ->done field
183  * set to @done, which should have been initialized with
184  * DEFINE_WB_COMPLETION().  This function returns after all such work items
185  * are completed.  Work items which are waited upon aren't freed
186  * automatically on completion.
187  */
wb_wait_for_completion(struct wb_completion * done)188 void wb_wait_for_completion(struct wb_completion *done)
189 {
190 	atomic_dec(&done->cnt);		/* put down the initial count */
191 	wait_event(*done->waitq, !atomic_read(&done->cnt));
192 }
193 
194 #ifdef CONFIG_CGROUP_WRITEBACK
195 
196 /*
197  * Parameters for foreign inode detection, see wbc_detach_inode() to see
198  * how they're used.
199  *
200  * These paramters are inherently heuristical as the detection target
201  * itself is fuzzy.  All we want to do is detaching an inode from the
202  * current owner if it's being written to by some other cgroups too much.
203  *
204  * The current cgroup writeback is built on the assumption that multiple
205  * cgroups writing to the same inode concurrently is very rare and a mode
206  * of operation which isn't well supported.  As such, the goal is not
207  * taking too long when a different cgroup takes over an inode while
208  * avoiding too aggressive flip-flops from occasional foreign writes.
209  *
210  * We record, very roughly, 2s worth of IO time history and if more than
211  * half of that is foreign, trigger the switch.  The recording is quantized
212  * to 16 slots.  To avoid tiny writes from swinging the decision too much,
213  * writes smaller than 1/8 of avg size are ignored.
214  */
215 #define WB_FRN_TIME_SHIFT	13	/* 1s = 2^13, upto 8 secs w/ 16bit */
216 #define WB_FRN_TIME_AVG_SHIFT	3	/* avg = avg * 7/8 + new * 1/8 */
217 #define WB_FRN_TIME_CUT_DIV	8	/* ignore rounds < avg / 8 */
218 #define WB_FRN_TIME_PERIOD	(2 * (1 << WB_FRN_TIME_SHIFT))	/* 2s */
219 
220 #define WB_FRN_HIST_SLOTS	16	/* inode->i_wb_frn_history is 16bit */
221 #define WB_FRN_HIST_UNIT	(WB_FRN_TIME_PERIOD / WB_FRN_HIST_SLOTS)
222 					/* each slot's duration is 2s / 16 */
223 #define WB_FRN_HIST_THR_SLOTS	(WB_FRN_HIST_SLOTS / 2)
224 					/* if foreign slots >= 8, switch */
225 #define WB_FRN_HIST_MAX_SLOTS	(WB_FRN_HIST_THR_SLOTS / 2 + 1)
226 					/* one round can affect upto 5 slots */
227 #define WB_FRN_MAX_IN_FLIGHT	1024	/* don't queue too many concurrently */
228 
229 /*
230  * Maximum inodes per isw.  A specific value has been chosen to make
231  * struct inode_switch_wbs_context fit into 1024 bytes kmalloc.
232  */
233 #define WB_MAX_INODES_PER_ISW  ((1024UL - sizeof(struct inode_switch_wbs_context)) \
234                                 / sizeof(struct inode *))
235 
236 static atomic_t isw_nr_in_flight = ATOMIC_INIT(0);
237 static struct workqueue_struct *isw_wq;
238 
__inode_attach_wb(struct inode * inode,struct page * page)239 void __inode_attach_wb(struct inode *inode, struct page *page)
240 {
241 	struct backing_dev_info *bdi = inode_to_bdi(inode);
242 	struct bdi_writeback *wb = NULL;
243 
244 	if (inode_cgwb_enabled(inode)) {
245 		struct cgroup_subsys_state *memcg_css;
246 
247 		if (page) {
248 			memcg_css = mem_cgroup_css_from_page(page);
249 			wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
250 		} else {
251 			/* must pin memcg_css, see wb_get_create() */
252 			memcg_css = task_get_css(current, memory_cgrp_id);
253 			wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
254 			css_put(memcg_css);
255 		}
256 	}
257 
258 	if (!wb)
259 		wb = &bdi->wb;
260 
261 	/*
262 	 * There may be multiple instances of this function racing to
263 	 * update the same inode.  Use cmpxchg() to tell the winner.
264 	 */
265 	if (unlikely(cmpxchg(&inode->i_wb, NULL, wb)))
266 		wb_put(wb);
267 }
268 EXPORT_SYMBOL_GPL(__inode_attach_wb);
269 
270 /**
271  * inode_cgwb_move_to_attached - put the inode onto wb->b_attached list
272  * @inode: inode of interest with i_lock held
273  * @wb: target bdi_writeback
274  *
275  * Remove the inode from wb's io lists and if necessarily put onto b_attached
276  * list.  Only inodes attached to cgwb's are kept on this list.
277  */
inode_cgwb_move_to_attached(struct inode * inode,struct bdi_writeback * wb)278 static void inode_cgwb_move_to_attached(struct inode *inode,
279 					struct bdi_writeback *wb)
280 {
281 	assert_spin_locked(&wb->list_lock);
282 	assert_spin_locked(&inode->i_lock);
283 
284 	inode->i_state &= ~I_SYNC_QUEUED;
285 	if (wb != &wb->bdi->wb)
286 		list_move(&inode->i_io_list, &wb->b_attached);
287 	else
288 		list_del_init(&inode->i_io_list);
289 	wb_io_lists_depopulated(wb);
290 }
291 
292 /**
293  * locked_inode_to_wb_and_lock_list - determine a locked inode's wb and lock it
294  * @inode: inode of interest with i_lock held
295  *
296  * Returns @inode's wb with its list_lock held.  @inode->i_lock must be
297  * held on entry and is released on return.  The returned wb is guaranteed
298  * to stay @inode's associated wb until its list_lock is released.
299  */
300 static struct bdi_writeback *
locked_inode_to_wb_and_lock_list(struct inode * inode)301 locked_inode_to_wb_and_lock_list(struct inode *inode)
302 	__releases(&inode->i_lock)
303 	__acquires(&wb->list_lock)
304 {
305 	while (true) {
306 		struct bdi_writeback *wb = inode_to_wb(inode);
307 
308 		/*
309 		 * inode_to_wb() association is protected by both
310 		 * @inode->i_lock and @wb->list_lock but list_lock nests
311 		 * outside i_lock.  Drop i_lock and verify that the
312 		 * association hasn't changed after acquiring list_lock.
313 		 */
314 		wb_get(wb);
315 		spin_unlock(&inode->i_lock);
316 		spin_lock(&wb->list_lock);
317 
318 		/* i_wb may have changed inbetween, can't use inode_to_wb() */
319 		if (likely(wb == inode->i_wb)) {
320 			wb_put(wb);	/* @inode already has ref */
321 			return wb;
322 		}
323 
324 		spin_unlock(&wb->list_lock);
325 		wb_put(wb);
326 		cpu_relax();
327 		spin_lock(&inode->i_lock);
328 	}
329 }
330 
331 /**
332  * inode_to_wb_and_lock_list - determine an inode's wb and lock it
333  * @inode: inode of interest
334  *
335  * Same as locked_inode_to_wb_and_lock_list() but @inode->i_lock isn't held
336  * on entry.
337  */
inode_to_wb_and_lock_list(struct inode * inode)338 static struct bdi_writeback *inode_to_wb_and_lock_list(struct inode *inode)
339 	__acquires(&wb->list_lock)
340 {
341 	spin_lock(&inode->i_lock);
342 	return locked_inode_to_wb_and_lock_list(inode);
343 }
344 
345 struct inode_switch_wbs_context {
346 	struct rcu_work		work;
347 
348 	/*
349 	 * Multiple inodes can be switched at once.  The switching procedure
350 	 * consists of two parts, separated by a RCU grace period.  To make
351 	 * sure that the second part is executed for each inode gone through
352 	 * the first part, all inode pointers are placed into a NULL-terminated
353 	 * array embedded into struct inode_switch_wbs_context.  Otherwise
354 	 * an inode could be left in a non-consistent state.
355 	 */
356 	struct bdi_writeback	*new_wb;
357 	struct inode		*inodes[];
358 };
359 
bdi_down_write_wb_switch_rwsem(struct backing_dev_info * bdi)360 static void bdi_down_write_wb_switch_rwsem(struct backing_dev_info *bdi)
361 {
362 	down_write(&bdi->wb_switch_rwsem);
363 }
364 
bdi_up_write_wb_switch_rwsem(struct backing_dev_info * bdi)365 static void bdi_up_write_wb_switch_rwsem(struct backing_dev_info *bdi)
366 {
367 	up_write(&bdi->wb_switch_rwsem);
368 }
369 
inode_do_switch_wbs(struct inode * inode,struct bdi_writeback * old_wb,struct bdi_writeback * new_wb)370 static bool inode_do_switch_wbs(struct inode *inode,
371 				struct bdi_writeback *old_wb,
372 				struct bdi_writeback *new_wb)
373 {
374 	struct address_space *mapping = inode->i_mapping;
375 	XA_STATE(xas, &mapping->i_pages, 0);
376 	struct folio *folio;
377 	bool switched = false;
378 
379 	spin_lock(&inode->i_lock);
380 	xa_lock_irq(&mapping->i_pages);
381 
382 	/*
383 	 * Once I_FREEING or I_WILL_FREE are visible under i_lock, the eviction
384 	 * path owns the inode and we shouldn't modify ->i_io_list.
385 	 */
386 	if (unlikely(inode->i_state & (I_FREEING | I_WILL_FREE)))
387 		goto skip_switch;
388 
389 	trace_inode_switch_wbs(inode, old_wb, new_wb);
390 
391 	/*
392 	 * Count and transfer stats.  Note that PAGECACHE_TAG_DIRTY points
393 	 * to possibly dirty folios while PAGECACHE_TAG_WRITEBACK points to
394 	 * folios actually under writeback.
395 	 */
396 	xas_for_each_marked(&xas, folio, ULONG_MAX, PAGECACHE_TAG_DIRTY) {
397 		if (folio_test_dirty(folio)) {
398 			long nr = folio_nr_pages(folio);
399 			wb_stat_mod(old_wb, WB_RECLAIMABLE, -nr);
400 			wb_stat_mod(new_wb, WB_RECLAIMABLE, nr);
401 		}
402 	}
403 
404 	xas_set(&xas, 0);
405 	xas_for_each_marked(&xas, folio, ULONG_MAX, PAGECACHE_TAG_WRITEBACK) {
406 		long nr = folio_nr_pages(folio);
407 		WARN_ON_ONCE(!folio_test_writeback(folio));
408 		wb_stat_mod(old_wb, WB_WRITEBACK, -nr);
409 		wb_stat_mod(new_wb, WB_WRITEBACK, nr);
410 	}
411 
412 	if (mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK)) {
413 		atomic_dec(&old_wb->writeback_inodes);
414 		atomic_inc(&new_wb->writeback_inodes);
415 	}
416 
417 	wb_get(new_wb);
418 
419 	/*
420 	 * Transfer to @new_wb's IO list if necessary.  If the @inode is dirty,
421 	 * the specific list @inode was on is ignored and the @inode is put on
422 	 * ->b_dirty which is always correct including from ->b_dirty_time.
423 	 * The transfer preserves @inode->dirtied_when ordering.  If the @inode
424 	 * was clean, it means it was on the b_attached list, so move it onto
425 	 * the b_attached list of @new_wb.
426 	 */
427 	if (!list_empty(&inode->i_io_list)) {
428 		inode->i_wb = new_wb;
429 
430 		if (inode->i_state & I_DIRTY_ALL) {
431 			struct inode *pos;
432 
433 			list_for_each_entry(pos, &new_wb->b_dirty, i_io_list)
434 				if (time_after_eq(inode->dirtied_when,
435 						  pos->dirtied_when))
436 					break;
437 			inode_io_list_move_locked(inode, new_wb,
438 						  pos->i_io_list.prev);
439 		} else {
440 			inode_cgwb_move_to_attached(inode, new_wb);
441 		}
442 	} else {
443 		inode->i_wb = new_wb;
444 	}
445 
446 	/* ->i_wb_frn updates may race wbc_detach_inode() but doesn't matter */
447 	inode->i_wb_frn_winner = 0;
448 	inode->i_wb_frn_avg_time = 0;
449 	inode->i_wb_frn_history = 0;
450 	switched = true;
451 skip_switch:
452 	/*
453 	 * Paired with load_acquire in unlocked_inode_to_wb_begin() and
454 	 * ensures that the new wb is visible if they see !I_WB_SWITCH.
455 	 */
456 	smp_store_release(&inode->i_state, inode->i_state & ~I_WB_SWITCH);
457 
458 	xa_unlock_irq(&mapping->i_pages);
459 	spin_unlock(&inode->i_lock);
460 
461 	return switched;
462 }
463 
inode_switch_wbs_work_fn(struct work_struct * work)464 static void inode_switch_wbs_work_fn(struct work_struct *work)
465 {
466 	struct inode_switch_wbs_context *isw =
467 		container_of(to_rcu_work(work), struct inode_switch_wbs_context, work);
468 	struct backing_dev_info *bdi = inode_to_bdi(isw->inodes[0]);
469 	struct bdi_writeback *old_wb = isw->inodes[0]->i_wb;
470 	struct bdi_writeback *new_wb = isw->new_wb;
471 	unsigned long nr_switched = 0;
472 	struct inode **inodep;
473 
474 	/*
475 	 * If @inode switches cgwb membership while sync_inodes_sb() is
476 	 * being issued, sync_inodes_sb() might miss it.  Synchronize.
477 	 */
478 	down_read(&bdi->wb_switch_rwsem);
479 
480 	/*
481 	 * By the time control reaches here, RCU grace period has passed
482 	 * since I_WB_SWITCH assertion and all wb stat update transactions
483 	 * between unlocked_inode_to_wb_begin/end() are guaranteed to be
484 	 * synchronizing against the i_pages lock.
485 	 *
486 	 * Grabbing old_wb->list_lock, inode->i_lock and the i_pages lock
487 	 * gives us exclusion against all wb related operations on @inode
488 	 * including IO list manipulations and stat updates.
489 	 */
490 	if (old_wb < new_wb) {
491 		spin_lock(&old_wb->list_lock);
492 		spin_lock_nested(&new_wb->list_lock, SINGLE_DEPTH_NESTING);
493 	} else {
494 		spin_lock(&new_wb->list_lock);
495 		spin_lock_nested(&old_wb->list_lock, SINGLE_DEPTH_NESTING);
496 	}
497 
498 	for (inodep = isw->inodes; *inodep; inodep++) {
499 		WARN_ON_ONCE((*inodep)->i_wb != old_wb);
500 		if (inode_do_switch_wbs(*inodep, old_wb, new_wb))
501 			nr_switched++;
502 	}
503 
504 	spin_unlock(&new_wb->list_lock);
505 	spin_unlock(&old_wb->list_lock);
506 
507 	up_read(&bdi->wb_switch_rwsem);
508 
509 	if (nr_switched) {
510 		wb_wakeup(new_wb);
511 		wb_put_many(old_wb, nr_switched);
512 	}
513 
514 	for (inodep = isw->inodes; *inodep; inodep++)
515 		iput(*inodep);
516 	wb_put(new_wb);
517 	kfree(isw);
518 	atomic_dec(&isw_nr_in_flight);
519 }
520 
inode_prepare_wbs_switch(struct inode * inode,struct bdi_writeback * new_wb)521 static bool inode_prepare_wbs_switch(struct inode *inode,
522 				     struct bdi_writeback *new_wb)
523 {
524 	/*
525 	 * Paired with smp_mb() in cgroup_writeback_umount().
526 	 * isw_nr_in_flight must be increased before checking SB_ACTIVE and
527 	 * grabbing an inode, otherwise isw_nr_in_flight can be observed as 0
528 	 * in cgroup_writeback_umount() and the isw_wq will be not flushed.
529 	 */
530 	smp_mb();
531 
532 	if (IS_DAX(inode))
533 		return false;
534 
535 	/* while holding I_WB_SWITCH, no one else can update the association */
536 	spin_lock(&inode->i_lock);
537 	if (!(inode->i_sb->s_flags & SB_ACTIVE) ||
538 	    inode->i_state & (I_WB_SWITCH | I_FREEING | I_WILL_FREE) ||
539 	    inode_to_wb(inode) == new_wb) {
540 		spin_unlock(&inode->i_lock);
541 		return false;
542 	}
543 	inode->i_state |= I_WB_SWITCH;
544 	__iget(inode);
545 	spin_unlock(&inode->i_lock);
546 
547 	return true;
548 }
549 
550 /**
551  * inode_switch_wbs - change the wb association of an inode
552  * @inode: target inode
553  * @new_wb_id: ID of the new wb
554  *
555  * Switch @inode's wb association to the wb identified by @new_wb_id.  The
556  * switching is performed asynchronously and may fail silently.
557  */
inode_switch_wbs(struct inode * inode,int new_wb_id)558 static void inode_switch_wbs(struct inode *inode, int new_wb_id)
559 {
560 	struct backing_dev_info *bdi = inode_to_bdi(inode);
561 	struct cgroup_subsys_state *memcg_css;
562 	struct inode_switch_wbs_context *isw;
563 
564 	/* noop if seems to be already in progress */
565 	if (inode->i_state & I_WB_SWITCH)
566 		return;
567 
568 	/* avoid queueing a new switch if too many are already in flight */
569 	if (atomic_read(&isw_nr_in_flight) > WB_FRN_MAX_IN_FLIGHT)
570 		return;
571 
572 	isw = kzalloc(struct_size(isw, inodes, 2), GFP_ATOMIC);
573 	if (!isw)
574 		return;
575 
576 	atomic_inc(&isw_nr_in_flight);
577 
578 	/* find and pin the new wb */
579 	rcu_read_lock();
580 	memcg_css = css_from_id(new_wb_id, &memory_cgrp_subsys);
581 	if (memcg_css && !css_tryget(memcg_css))
582 		memcg_css = NULL;
583 	rcu_read_unlock();
584 	if (!memcg_css)
585 		goto out_free;
586 
587 	isw->new_wb = wb_get_create(bdi, memcg_css, GFP_ATOMIC);
588 	css_put(memcg_css);
589 	if (!isw->new_wb)
590 		goto out_free;
591 
592 	if (!inode_prepare_wbs_switch(inode, isw->new_wb))
593 		goto out_free;
594 
595 	isw->inodes[0] = inode;
596 
597 	/*
598 	 * In addition to synchronizing among switchers, I_WB_SWITCH tells
599 	 * the RCU protected stat update paths to grab the i_page
600 	 * lock so that stat transfer can synchronize against them.
601 	 * Let's continue after I_WB_SWITCH is guaranteed to be visible.
602 	 */
603 	INIT_RCU_WORK(&isw->work, inode_switch_wbs_work_fn);
604 	queue_rcu_work(isw_wq, &isw->work);
605 	return;
606 
607 out_free:
608 	atomic_dec(&isw_nr_in_flight);
609 	if (isw->new_wb)
610 		wb_put(isw->new_wb);
611 	kfree(isw);
612 }
613 
614 /**
615  * cleanup_offline_cgwb - detach associated inodes
616  * @wb: target wb
617  *
618  * Switch all inodes attached to @wb to a nearest living ancestor's wb in order
619  * to eventually release the dying @wb.  Returns %true if not all inodes were
620  * switched and the function has to be restarted.
621  */
cleanup_offline_cgwb(struct bdi_writeback * wb)622 bool cleanup_offline_cgwb(struct bdi_writeback *wb)
623 {
624 	struct cgroup_subsys_state *memcg_css;
625 	struct inode_switch_wbs_context *isw;
626 	struct inode *inode;
627 	int nr;
628 	bool restart = false;
629 
630 	isw = kzalloc(struct_size(isw, inodes, WB_MAX_INODES_PER_ISW),
631 		      GFP_KERNEL);
632 	if (!isw)
633 		return restart;
634 
635 	atomic_inc(&isw_nr_in_flight);
636 
637 	for (memcg_css = wb->memcg_css->parent; memcg_css;
638 	     memcg_css = memcg_css->parent) {
639 		isw->new_wb = wb_get_create(wb->bdi, memcg_css, GFP_KERNEL);
640 		if (isw->new_wb)
641 			break;
642 	}
643 	if (unlikely(!isw->new_wb))
644 		isw->new_wb = &wb->bdi->wb; /* wb_get() is noop for bdi's wb */
645 
646 	nr = 0;
647 	spin_lock(&wb->list_lock);
648 	list_for_each_entry(inode, &wb->b_attached, i_io_list) {
649 		if (!inode_prepare_wbs_switch(inode, isw->new_wb))
650 			continue;
651 
652 		isw->inodes[nr++] = inode;
653 
654 		if (nr >= WB_MAX_INODES_PER_ISW - 1) {
655 			restart = true;
656 			break;
657 		}
658 	}
659 	spin_unlock(&wb->list_lock);
660 
661 	/* no attached inodes? bail out */
662 	if (nr == 0) {
663 		atomic_dec(&isw_nr_in_flight);
664 		wb_put(isw->new_wb);
665 		kfree(isw);
666 		return restart;
667 	}
668 
669 	/*
670 	 * In addition to synchronizing among switchers, I_WB_SWITCH tells
671 	 * the RCU protected stat update paths to grab the i_page
672 	 * lock so that stat transfer can synchronize against them.
673 	 * Let's continue after I_WB_SWITCH is guaranteed to be visible.
674 	 */
675 	INIT_RCU_WORK(&isw->work, inode_switch_wbs_work_fn);
676 	queue_rcu_work(isw_wq, &isw->work);
677 
678 	return restart;
679 }
680 
681 /**
682  * wbc_attach_and_unlock_inode - associate wbc with target inode and unlock it
683  * @wbc: writeback_control of interest
684  * @inode: target inode
685  *
686  * @inode is locked and about to be written back under the control of @wbc.
687  * Record @inode's writeback context into @wbc and unlock the i_lock.  On
688  * writeback completion, wbc_detach_inode() should be called.  This is used
689  * to track the cgroup writeback context.
690  */
wbc_attach_and_unlock_inode(struct writeback_control * wbc,struct inode * inode)691 void wbc_attach_and_unlock_inode(struct writeback_control *wbc,
692 				 struct inode *inode)
693 {
694 	if (!inode_cgwb_enabled(inode)) {
695 		spin_unlock(&inode->i_lock);
696 		return;
697 	}
698 
699 	wbc->wb = inode_to_wb(inode);
700 	wbc->inode = inode;
701 
702 	wbc->wb_id = wbc->wb->memcg_css->id;
703 	wbc->wb_lcand_id = inode->i_wb_frn_winner;
704 	wbc->wb_tcand_id = 0;
705 	wbc->wb_bytes = 0;
706 	wbc->wb_lcand_bytes = 0;
707 	wbc->wb_tcand_bytes = 0;
708 
709 	wb_get(wbc->wb);
710 	spin_unlock(&inode->i_lock);
711 
712 	/*
713 	 * A dying wb indicates that either the blkcg associated with the
714 	 * memcg changed or the associated memcg is dying.  In the first
715 	 * case, a replacement wb should already be available and we should
716 	 * refresh the wb immediately.  In the second case, trying to
717 	 * refresh will keep failing.
718 	 */
719 	if (unlikely(wb_dying(wbc->wb) && !css_is_dying(wbc->wb->memcg_css)))
720 		inode_switch_wbs(inode, wbc->wb_id);
721 }
722 EXPORT_SYMBOL_GPL(wbc_attach_and_unlock_inode);
723 
724 /**
725  * wbc_detach_inode - disassociate wbc from inode and perform foreign detection
726  * @wbc: writeback_control of the just finished writeback
727  *
728  * To be called after a writeback attempt of an inode finishes and undoes
729  * wbc_attach_and_unlock_inode().  Can be called under any context.
730  *
731  * As concurrent write sharing of an inode is expected to be very rare and
732  * memcg only tracks page ownership on first-use basis severely confining
733  * the usefulness of such sharing, cgroup writeback tracks ownership
734  * per-inode.  While the support for concurrent write sharing of an inode
735  * is deemed unnecessary, an inode being written to by different cgroups at
736  * different points in time is a lot more common, and, more importantly,
737  * charging only by first-use can too readily lead to grossly incorrect
738  * behaviors (single foreign page can lead to gigabytes of writeback to be
739  * incorrectly attributed).
740  *
741  * To resolve this issue, cgroup writeback detects the majority dirtier of
742  * an inode and transfers the ownership to it.  To avoid unnecessary
743  * oscillation, the detection mechanism keeps track of history and gives
744  * out the switch verdict only if the foreign usage pattern is stable over
745  * a certain amount of time and/or writeback attempts.
746  *
747  * On each writeback attempt, @wbc tries to detect the majority writer
748  * using Boyer-Moore majority vote algorithm.  In addition to the byte
749  * count from the majority voting, it also counts the bytes written for the
750  * current wb and the last round's winner wb (max of last round's current
751  * wb, the winner from two rounds ago, and the last round's majority
752  * candidate).  Keeping track of the historical winner helps the algorithm
753  * to semi-reliably detect the most active writer even when it's not the
754  * absolute majority.
755  *
756  * Once the winner of the round is determined, whether the winner is
757  * foreign or not and how much IO time the round consumed is recorded in
758  * inode->i_wb_frn_history.  If the amount of recorded foreign IO time is
759  * over a certain threshold, the switch verdict is given.
760  */
wbc_detach_inode(struct writeback_control * wbc)761 void wbc_detach_inode(struct writeback_control *wbc)
762 {
763 	struct bdi_writeback *wb = wbc->wb;
764 	struct inode *inode = wbc->inode;
765 	unsigned long avg_time, max_bytes, max_time;
766 	u16 history;
767 	int max_id;
768 
769 	if (!wb)
770 		return;
771 
772 	history = inode->i_wb_frn_history;
773 	avg_time = inode->i_wb_frn_avg_time;
774 
775 	/* pick the winner of this round */
776 	if (wbc->wb_bytes >= wbc->wb_lcand_bytes &&
777 	    wbc->wb_bytes >= wbc->wb_tcand_bytes) {
778 		max_id = wbc->wb_id;
779 		max_bytes = wbc->wb_bytes;
780 	} else if (wbc->wb_lcand_bytes >= wbc->wb_tcand_bytes) {
781 		max_id = wbc->wb_lcand_id;
782 		max_bytes = wbc->wb_lcand_bytes;
783 	} else {
784 		max_id = wbc->wb_tcand_id;
785 		max_bytes = wbc->wb_tcand_bytes;
786 	}
787 
788 	/*
789 	 * Calculate the amount of IO time the winner consumed and fold it
790 	 * into the running average kept per inode.  If the consumed IO
791 	 * time is lower than avag / WB_FRN_TIME_CUT_DIV, ignore it for
792 	 * deciding whether to switch or not.  This is to prevent one-off
793 	 * small dirtiers from skewing the verdict.
794 	 */
795 	max_time = DIV_ROUND_UP((max_bytes >> PAGE_SHIFT) << WB_FRN_TIME_SHIFT,
796 				wb->avg_write_bandwidth);
797 	if (avg_time)
798 		avg_time += (max_time >> WB_FRN_TIME_AVG_SHIFT) -
799 			    (avg_time >> WB_FRN_TIME_AVG_SHIFT);
800 	else
801 		avg_time = max_time;	/* immediate catch up on first run */
802 
803 	if (max_time >= avg_time / WB_FRN_TIME_CUT_DIV) {
804 		int slots;
805 
806 		/*
807 		 * The switch verdict is reached if foreign wb's consume
808 		 * more than a certain proportion of IO time in a
809 		 * WB_FRN_TIME_PERIOD.  This is loosely tracked by 16 slot
810 		 * history mask where each bit represents one sixteenth of
811 		 * the period.  Determine the number of slots to shift into
812 		 * history from @max_time.
813 		 */
814 		slots = min(DIV_ROUND_UP(max_time, WB_FRN_HIST_UNIT),
815 			    (unsigned long)WB_FRN_HIST_MAX_SLOTS);
816 		history <<= slots;
817 		if (wbc->wb_id != max_id)
818 			history |= (1U << slots) - 1;
819 
820 		if (history)
821 			trace_inode_foreign_history(inode, wbc, history);
822 
823 		/*
824 		 * Switch if the current wb isn't the consistent winner.
825 		 * If there are multiple closely competing dirtiers, the
826 		 * inode may switch across them repeatedly over time, which
827 		 * is okay.  The main goal is avoiding keeping an inode on
828 		 * the wrong wb for an extended period of time.
829 		 */
830 		if (hweight32(history) > WB_FRN_HIST_THR_SLOTS)
831 			inode_switch_wbs(inode, max_id);
832 	}
833 
834 	/*
835 	 * Multiple instances of this function may race to update the
836 	 * following fields but we don't mind occassional inaccuracies.
837 	 */
838 	inode->i_wb_frn_winner = max_id;
839 	inode->i_wb_frn_avg_time = min(avg_time, (unsigned long)U16_MAX);
840 	inode->i_wb_frn_history = history;
841 
842 	wb_put(wbc->wb);
843 	wbc->wb = NULL;
844 }
845 EXPORT_SYMBOL_GPL(wbc_detach_inode);
846 
847 /**
848  * wbc_account_cgroup_owner - account writeback to update inode cgroup ownership
849  * @wbc: writeback_control of the writeback in progress
850  * @page: page being written out
851  * @bytes: number of bytes being written out
852  *
853  * @bytes from @page are about to written out during the writeback
854  * controlled by @wbc.  Keep the book for foreign inode detection.  See
855  * wbc_detach_inode().
856  */
wbc_account_cgroup_owner(struct writeback_control * wbc,struct page * page,size_t bytes)857 void wbc_account_cgroup_owner(struct writeback_control *wbc, struct page *page,
858 			      size_t bytes)
859 {
860 	struct cgroup_subsys_state *css;
861 	int id;
862 
863 	/*
864 	 * pageout() path doesn't attach @wbc to the inode being written
865 	 * out.  This is intentional as we don't want the function to block
866 	 * behind a slow cgroup.  Ultimately, we want pageout() to kick off
867 	 * regular writeback instead of writing things out itself.
868 	 */
869 	if (!wbc->wb || wbc->no_cgroup_owner)
870 		return;
871 
872 	css = mem_cgroup_css_from_page(page);
873 	/* dead cgroups shouldn't contribute to inode ownership arbitration */
874 	if (!(css->flags & CSS_ONLINE))
875 		return;
876 
877 	id = css->id;
878 
879 	if (id == wbc->wb_id) {
880 		wbc->wb_bytes += bytes;
881 		return;
882 	}
883 
884 	if (id == wbc->wb_lcand_id)
885 		wbc->wb_lcand_bytes += bytes;
886 
887 	/* Boyer-Moore majority vote algorithm */
888 	if (!wbc->wb_tcand_bytes)
889 		wbc->wb_tcand_id = id;
890 	if (id == wbc->wb_tcand_id)
891 		wbc->wb_tcand_bytes += bytes;
892 	else
893 		wbc->wb_tcand_bytes -= min(bytes, wbc->wb_tcand_bytes);
894 }
895 EXPORT_SYMBOL_GPL(wbc_account_cgroup_owner);
896 
897 /**
898  * wb_split_bdi_pages - split nr_pages to write according to bandwidth
899  * @wb: target bdi_writeback to split @nr_pages to
900  * @nr_pages: number of pages to write for the whole bdi
901  *
902  * Split @wb's portion of @nr_pages according to @wb's write bandwidth in
903  * relation to the total write bandwidth of all wb's w/ dirty inodes on
904  * @wb->bdi.
905  */
wb_split_bdi_pages(struct bdi_writeback * wb,long nr_pages)906 static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
907 {
908 	unsigned long this_bw = wb->avg_write_bandwidth;
909 	unsigned long tot_bw = atomic_long_read(&wb->bdi->tot_write_bandwidth);
910 
911 	if (nr_pages == LONG_MAX)
912 		return LONG_MAX;
913 
914 	/*
915 	 * This may be called on clean wb's and proportional distribution
916 	 * may not make sense, just use the original @nr_pages in those
917 	 * cases.  In general, we wanna err on the side of writing more.
918 	 */
919 	if (!tot_bw || this_bw >= tot_bw)
920 		return nr_pages;
921 	else
922 		return DIV_ROUND_UP_ULL((u64)nr_pages * this_bw, tot_bw);
923 }
924 
925 /**
926  * bdi_split_work_to_wbs - split a wb_writeback_work to all wb's of a bdi
927  * @bdi: target backing_dev_info
928  * @base_work: wb_writeback_work to issue
929  * @skip_if_busy: skip wb's which already have writeback in progress
930  *
931  * Split and issue @base_work to all wb's (bdi_writeback's) of @bdi which
932  * have dirty inodes.  If @base_work->nr_page isn't %LONG_MAX, it's
933  * distributed to the busy wbs according to each wb's proportion in the
934  * total active write bandwidth of @bdi.
935  */
bdi_split_work_to_wbs(struct backing_dev_info * bdi,struct wb_writeback_work * base_work,bool skip_if_busy)936 static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
937 				  struct wb_writeback_work *base_work,
938 				  bool skip_if_busy)
939 {
940 	struct bdi_writeback *last_wb = NULL;
941 	struct bdi_writeback *wb = list_entry(&bdi->wb_list,
942 					      struct bdi_writeback, bdi_node);
943 
944 	might_sleep();
945 restart:
946 	rcu_read_lock();
947 	list_for_each_entry_continue_rcu(wb, &bdi->wb_list, bdi_node) {
948 		DEFINE_WB_COMPLETION(fallback_work_done, bdi);
949 		struct wb_writeback_work fallback_work;
950 		struct wb_writeback_work *work;
951 		long nr_pages;
952 
953 		if (last_wb) {
954 			wb_put(last_wb);
955 			last_wb = NULL;
956 		}
957 
958 		/* SYNC_ALL writes out I_DIRTY_TIME too */
959 		if (!wb_has_dirty_io(wb) &&
960 		    (base_work->sync_mode == WB_SYNC_NONE ||
961 		     list_empty(&wb->b_dirty_time)))
962 			continue;
963 		if (skip_if_busy && writeback_in_progress(wb))
964 			continue;
965 
966 		nr_pages = wb_split_bdi_pages(wb, base_work->nr_pages);
967 
968 		work = kmalloc(sizeof(*work), GFP_ATOMIC);
969 		if (work) {
970 			*work = *base_work;
971 			work->nr_pages = nr_pages;
972 			work->auto_free = 1;
973 			wb_queue_work(wb, work);
974 			continue;
975 		}
976 
977 		/* alloc failed, execute synchronously using on-stack fallback */
978 		work = &fallback_work;
979 		*work = *base_work;
980 		work->nr_pages = nr_pages;
981 		work->auto_free = 0;
982 		work->done = &fallback_work_done;
983 
984 		wb_queue_work(wb, work);
985 
986 		/*
987 		 * Pin @wb so that it stays on @bdi->wb_list.  This allows
988 		 * continuing iteration from @wb after dropping and
989 		 * regrabbing rcu read lock.
990 		 */
991 		wb_get(wb);
992 		last_wb = wb;
993 
994 		rcu_read_unlock();
995 		wb_wait_for_completion(&fallback_work_done);
996 		goto restart;
997 	}
998 	rcu_read_unlock();
999 
1000 	if (last_wb)
1001 		wb_put(last_wb);
1002 }
1003 
1004 /**
1005  * cgroup_writeback_by_id - initiate cgroup writeback from bdi and memcg IDs
1006  * @bdi_id: target bdi id
1007  * @memcg_id: target memcg css id
1008  * @reason: reason why some writeback work initiated
1009  * @done: target wb_completion
1010  *
1011  * Initiate flush of the bdi_writeback identified by @bdi_id and @memcg_id
1012  * with the specified parameters.
1013  */
cgroup_writeback_by_id(u64 bdi_id,int memcg_id,enum wb_reason reason,struct wb_completion * done)1014 int cgroup_writeback_by_id(u64 bdi_id, int memcg_id,
1015 			   enum wb_reason reason, struct wb_completion *done)
1016 {
1017 	struct backing_dev_info *bdi;
1018 	struct cgroup_subsys_state *memcg_css;
1019 	struct bdi_writeback *wb;
1020 	struct wb_writeback_work *work;
1021 	unsigned long dirty;
1022 	int ret;
1023 
1024 	/* lookup bdi and memcg */
1025 	bdi = bdi_get_by_id(bdi_id);
1026 	if (!bdi)
1027 		return -ENOENT;
1028 
1029 	rcu_read_lock();
1030 	memcg_css = css_from_id(memcg_id, &memory_cgrp_subsys);
1031 	if (memcg_css && !css_tryget(memcg_css))
1032 		memcg_css = NULL;
1033 	rcu_read_unlock();
1034 	if (!memcg_css) {
1035 		ret = -ENOENT;
1036 		goto out_bdi_put;
1037 	}
1038 
1039 	/*
1040 	 * And find the associated wb.  If the wb isn't there already
1041 	 * there's nothing to flush, don't create one.
1042 	 */
1043 	wb = wb_get_lookup(bdi, memcg_css);
1044 	if (!wb) {
1045 		ret = -ENOENT;
1046 		goto out_css_put;
1047 	}
1048 
1049 	/*
1050 	 * The caller is attempting to write out most of
1051 	 * the currently dirty pages.  Let's take the current dirty page
1052 	 * count and inflate it by 25% which should be large enough to
1053 	 * flush out most dirty pages while avoiding getting livelocked by
1054 	 * concurrent dirtiers.
1055 	 *
1056 	 * BTW the memcg stats are flushed periodically and this is best-effort
1057 	 * estimation, so some potential error is ok.
1058 	 */
1059 	dirty = memcg_page_state(mem_cgroup_from_css(memcg_css), NR_FILE_DIRTY);
1060 	dirty = dirty * 10 / 8;
1061 
1062 	/* issue the writeback work */
1063 	work = kzalloc(sizeof(*work), GFP_NOWAIT | __GFP_NOWARN);
1064 	if (work) {
1065 		work->nr_pages = dirty;
1066 		work->sync_mode = WB_SYNC_NONE;
1067 		work->range_cyclic = 1;
1068 		work->reason = reason;
1069 		work->done = done;
1070 		work->auto_free = 1;
1071 		wb_queue_work(wb, work);
1072 		ret = 0;
1073 	} else {
1074 		ret = -ENOMEM;
1075 	}
1076 
1077 	wb_put(wb);
1078 out_css_put:
1079 	css_put(memcg_css);
1080 out_bdi_put:
1081 	bdi_put(bdi);
1082 	return ret;
1083 }
1084 
1085 /**
1086  * cgroup_writeback_umount - flush inode wb switches for umount
1087  *
1088  * This function is called when a super_block is about to be destroyed and
1089  * flushes in-flight inode wb switches.  An inode wb switch goes through
1090  * RCU and then workqueue, so the two need to be flushed in order to ensure
1091  * that all previously scheduled switches are finished.  As wb switches are
1092  * rare occurrences and synchronize_rcu() can take a while, perform
1093  * flushing iff wb switches are in flight.
1094  */
cgroup_writeback_umount(void)1095 void cgroup_writeback_umount(void)
1096 {
1097 	/*
1098 	 * SB_ACTIVE should be reliably cleared before checking
1099 	 * isw_nr_in_flight, see generic_shutdown_super().
1100 	 */
1101 	smp_mb();
1102 
1103 	if (atomic_read(&isw_nr_in_flight)) {
1104 		/*
1105 		 * Use rcu_barrier() to wait for all pending callbacks to
1106 		 * ensure that all in-flight wb switches are in the workqueue.
1107 		 */
1108 		rcu_barrier();
1109 		flush_workqueue(isw_wq);
1110 	}
1111 }
1112 
cgroup_writeback_init(void)1113 static int __init cgroup_writeback_init(void)
1114 {
1115 	isw_wq = alloc_workqueue("inode_switch_wbs", 0, 0);
1116 	if (!isw_wq)
1117 		return -ENOMEM;
1118 	return 0;
1119 }
1120 fs_initcall(cgroup_writeback_init);
1121 
1122 #else	/* CONFIG_CGROUP_WRITEBACK */
1123 
bdi_down_write_wb_switch_rwsem(struct backing_dev_info * bdi)1124 static void bdi_down_write_wb_switch_rwsem(struct backing_dev_info *bdi) { }
bdi_up_write_wb_switch_rwsem(struct backing_dev_info * bdi)1125 static void bdi_up_write_wb_switch_rwsem(struct backing_dev_info *bdi) { }
1126 
inode_cgwb_move_to_attached(struct inode * inode,struct bdi_writeback * wb)1127 static void inode_cgwb_move_to_attached(struct inode *inode,
1128 					struct bdi_writeback *wb)
1129 {
1130 	assert_spin_locked(&wb->list_lock);
1131 	assert_spin_locked(&inode->i_lock);
1132 
1133 	inode->i_state &= ~I_SYNC_QUEUED;
1134 	list_del_init(&inode->i_io_list);
1135 	wb_io_lists_depopulated(wb);
1136 }
1137 
1138 static struct bdi_writeback *
locked_inode_to_wb_and_lock_list(struct inode * inode)1139 locked_inode_to_wb_and_lock_list(struct inode *inode)
1140 	__releases(&inode->i_lock)
1141 	__acquires(&wb->list_lock)
1142 {
1143 	struct bdi_writeback *wb = inode_to_wb(inode);
1144 
1145 	spin_unlock(&inode->i_lock);
1146 	spin_lock(&wb->list_lock);
1147 	return wb;
1148 }
1149 
inode_to_wb_and_lock_list(struct inode * inode)1150 static struct bdi_writeback *inode_to_wb_and_lock_list(struct inode *inode)
1151 	__acquires(&wb->list_lock)
1152 {
1153 	struct bdi_writeback *wb = inode_to_wb(inode);
1154 
1155 	spin_lock(&wb->list_lock);
1156 	return wb;
1157 }
1158 
wb_split_bdi_pages(struct bdi_writeback * wb,long nr_pages)1159 static long wb_split_bdi_pages(struct bdi_writeback *wb, long nr_pages)
1160 {
1161 	return nr_pages;
1162 }
1163 
bdi_split_work_to_wbs(struct backing_dev_info * bdi,struct wb_writeback_work * base_work,bool skip_if_busy)1164 static void bdi_split_work_to_wbs(struct backing_dev_info *bdi,
1165 				  struct wb_writeback_work *base_work,
1166 				  bool skip_if_busy)
1167 {
1168 	might_sleep();
1169 
1170 	if (!skip_if_busy || !writeback_in_progress(&bdi->wb)) {
1171 		base_work->auto_free = 0;
1172 		wb_queue_work(&bdi->wb, base_work);
1173 	}
1174 }
1175 
1176 #endif	/* CONFIG_CGROUP_WRITEBACK */
1177 
1178 /*
1179  * Add in the number of potentially dirty inodes, because each inode
1180  * write can dirty pagecache in the underlying blockdev.
1181  */
get_nr_dirty_pages(void)1182 static unsigned long get_nr_dirty_pages(void)
1183 {
1184 	return global_node_page_state(NR_FILE_DIRTY) +
1185 		get_nr_dirty_inodes();
1186 }
1187 
wb_start_writeback(struct bdi_writeback * wb,enum wb_reason reason)1188 static void wb_start_writeback(struct bdi_writeback *wb, enum wb_reason reason)
1189 {
1190 	if (!wb_has_dirty_io(wb))
1191 		return;
1192 
1193 	/*
1194 	 * All callers of this function want to start writeback of all
1195 	 * dirty pages. Places like vmscan can call this at a very
1196 	 * high frequency, causing pointless allocations of tons of
1197 	 * work items and keeping the flusher threads busy retrieving
1198 	 * that work. Ensure that we only allow one of them pending and
1199 	 * inflight at the time.
1200 	 */
1201 	if (test_bit(WB_start_all, &wb->state) ||
1202 	    test_and_set_bit(WB_start_all, &wb->state))
1203 		return;
1204 
1205 	wb->start_all_reason = reason;
1206 	wb_wakeup(wb);
1207 }
1208 
1209 /**
1210  * wb_start_background_writeback - start background writeback
1211  * @wb: bdi_writback to write from
1212  *
1213  * Description:
1214  *   This makes sure WB_SYNC_NONE background writeback happens. When
1215  *   this function returns, it is only guaranteed that for given wb
1216  *   some IO is happening if we are over background dirty threshold.
1217  *   Caller need not hold sb s_umount semaphore.
1218  */
wb_start_background_writeback(struct bdi_writeback * wb)1219 void wb_start_background_writeback(struct bdi_writeback *wb)
1220 {
1221 	/*
1222 	 * We just wake up the flusher thread. It will perform background
1223 	 * writeback as soon as there is no other work to do.
1224 	 */
1225 	trace_writeback_wake_background(wb);
1226 	wb_wakeup(wb);
1227 }
1228 
1229 /*
1230  * Remove the inode from the writeback list it is on.
1231  */
inode_io_list_del(struct inode * inode)1232 void inode_io_list_del(struct inode *inode)
1233 {
1234 	struct bdi_writeback *wb;
1235 
1236 	wb = inode_to_wb_and_lock_list(inode);
1237 	spin_lock(&inode->i_lock);
1238 
1239 	inode->i_state &= ~I_SYNC_QUEUED;
1240 	list_del_init(&inode->i_io_list);
1241 	wb_io_lists_depopulated(wb);
1242 
1243 	spin_unlock(&inode->i_lock);
1244 	spin_unlock(&wb->list_lock);
1245 }
1246 EXPORT_SYMBOL(inode_io_list_del);
1247 
1248 /*
1249  * mark an inode as under writeback on the sb
1250  */
sb_mark_inode_writeback(struct inode * inode)1251 void sb_mark_inode_writeback(struct inode *inode)
1252 {
1253 	struct super_block *sb = inode->i_sb;
1254 	unsigned long flags;
1255 
1256 	if (list_empty(&inode->i_wb_list)) {
1257 		spin_lock_irqsave(&sb->s_inode_wblist_lock, flags);
1258 		if (list_empty(&inode->i_wb_list)) {
1259 			list_add_tail(&inode->i_wb_list, &sb->s_inodes_wb);
1260 			trace_sb_mark_inode_writeback(inode);
1261 		}
1262 		spin_unlock_irqrestore(&sb->s_inode_wblist_lock, flags);
1263 	}
1264 }
1265 
1266 /*
1267  * clear an inode as under writeback on the sb
1268  */
sb_clear_inode_writeback(struct inode * inode)1269 void sb_clear_inode_writeback(struct inode *inode)
1270 {
1271 	struct super_block *sb = inode->i_sb;
1272 	unsigned long flags;
1273 
1274 	if (!list_empty(&inode->i_wb_list)) {
1275 		spin_lock_irqsave(&sb->s_inode_wblist_lock, flags);
1276 		if (!list_empty(&inode->i_wb_list)) {
1277 			list_del_init(&inode->i_wb_list);
1278 			trace_sb_clear_inode_writeback(inode);
1279 		}
1280 		spin_unlock_irqrestore(&sb->s_inode_wblist_lock, flags);
1281 	}
1282 }
1283 
1284 /*
1285  * Redirty an inode: set its when-it-was dirtied timestamp and move it to the
1286  * furthest end of its superblock's dirty-inode list.
1287  *
1288  * Before stamping the inode's ->dirtied_when, we check to see whether it is
1289  * already the most-recently-dirtied inode on the b_dirty list.  If that is
1290  * the case then the inode must have been redirtied while it was being written
1291  * out and we don't reset its dirtied_when.
1292  */
redirty_tail_locked(struct inode * inode,struct bdi_writeback * wb)1293 static void redirty_tail_locked(struct inode *inode, struct bdi_writeback *wb)
1294 {
1295 	assert_spin_locked(&inode->i_lock);
1296 
1297 	if (!list_empty(&wb->b_dirty)) {
1298 		struct inode *tail;
1299 
1300 		tail = wb_inode(wb->b_dirty.next);
1301 		if (time_before(inode->dirtied_when, tail->dirtied_when))
1302 			inode->dirtied_when = jiffies;
1303 	}
1304 	inode_io_list_move_locked(inode, wb, &wb->b_dirty);
1305 	inode->i_state &= ~I_SYNC_QUEUED;
1306 }
1307 
redirty_tail(struct inode * inode,struct bdi_writeback * wb)1308 static void redirty_tail(struct inode *inode, struct bdi_writeback *wb)
1309 {
1310 	spin_lock(&inode->i_lock);
1311 	redirty_tail_locked(inode, wb);
1312 	spin_unlock(&inode->i_lock);
1313 }
1314 
1315 /*
1316  * requeue inode for re-scanning after bdi->b_io list is exhausted.
1317  */
requeue_io(struct inode * inode,struct bdi_writeback * wb)1318 static void requeue_io(struct inode *inode, struct bdi_writeback *wb)
1319 {
1320 	inode_io_list_move_locked(inode, wb, &wb->b_more_io);
1321 }
1322 
inode_sync_complete(struct inode * inode)1323 static void inode_sync_complete(struct inode *inode)
1324 {
1325 	inode->i_state &= ~I_SYNC;
1326 	/* If inode is clean an unused, put it into LRU now... */
1327 	inode_add_lru(inode);
1328 	/* Waiters must see I_SYNC cleared before being woken up */
1329 	smp_mb();
1330 	wake_up_bit(&inode->i_state, __I_SYNC);
1331 }
1332 
inode_dirtied_after(struct inode * inode,unsigned long t)1333 static bool inode_dirtied_after(struct inode *inode, unsigned long t)
1334 {
1335 	bool ret = time_after(inode->dirtied_when, t);
1336 #ifndef CONFIG_64BIT
1337 	/*
1338 	 * For inodes being constantly redirtied, dirtied_when can get stuck.
1339 	 * It _appears_ to be in the future, but is actually in distant past.
1340 	 * This test is necessary to prevent such wrapped-around relative times
1341 	 * from permanently stopping the whole bdi writeback.
1342 	 */
1343 	ret = ret && time_before_eq(inode->dirtied_when, jiffies);
1344 #endif
1345 	return ret;
1346 }
1347 
1348 #define EXPIRE_DIRTY_ATIME 0x0001
1349 
1350 /*
1351  * Move expired (dirtied before dirtied_before) dirty inodes from
1352  * @delaying_queue to @dispatch_queue.
1353  */
move_expired_inodes(struct list_head * delaying_queue,struct list_head * dispatch_queue,unsigned long dirtied_before)1354 static int move_expired_inodes(struct list_head *delaying_queue,
1355 			       struct list_head *dispatch_queue,
1356 			       unsigned long dirtied_before)
1357 {
1358 	LIST_HEAD(tmp);
1359 	struct list_head *pos, *node;
1360 	struct super_block *sb = NULL;
1361 	struct inode *inode;
1362 	int do_sb_sort = 0;
1363 	int moved = 0;
1364 
1365 	while (!list_empty(delaying_queue)) {
1366 		inode = wb_inode(delaying_queue->prev);
1367 		if (inode_dirtied_after(inode, dirtied_before))
1368 			break;
1369 		spin_lock(&inode->i_lock);
1370 		list_move(&inode->i_io_list, &tmp);
1371 		moved++;
1372 		inode->i_state |= I_SYNC_QUEUED;
1373 		spin_unlock(&inode->i_lock);
1374 		if (sb_is_blkdev_sb(inode->i_sb))
1375 			continue;
1376 		if (sb && sb != inode->i_sb)
1377 			do_sb_sort = 1;
1378 		sb = inode->i_sb;
1379 	}
1380 
1381 	/* just one sb in list, splice to dispatch_queue and we're done */
1382 	if (!do_sb_sort) {
1383 		list_splice(&tmp, dispatch_queue);
1384 		goto out;
1385 	}
1386 
1387 	/*
1388 	 * Although inode's i_io_list is moved from 'tmp' to 'dispatch_queue',
1389 	 * we don't take inode->i_lock here because it is just a pointless overhead.
1390 	 * Inode is already marked as I_SYNC_QUEUED so writeback list handling is
1391 	 * fully under our control.
1392 	 */
1393 	while (!list_empty(&tmp)) {
1394 		sb = wb_inode(tmp.prev)->i_sb;
1395 		list_for_each_prev_safe(pos, node, &tmp) {
1396 			inode = wb_inode(pos);
1397 			if (inode->i_sb == sb)
1398 				list_move(&inode->i_io_list, dispatch_queue);
1399 		}
1400 	}
1401 out:
1402 	return moved;
1403 }
1404 
1405 /*
1406  * Queue all expired dirty inodes for io, eldest first.
1407  * Before
1408  *         newly dirtied     b_dirty    b_io    b_more_io
1409  *         =============>    gf         edc     BA
1410  * After
1411  *         newly dirtied     b_dirty    b_io    b_more_io
1412  *         =============>    g          fBAedc
1413  *                                           |
1414  *                                           +--> dequeue for IO
1415  */
queue_io(struct bdi_writeback * wb,struct wb_writeback_work * work,unsigned long dirtied_before)1416 static void queue_io(struct bdi_writeback *wb, struct wb_writeback_work *work,
1417 		     unsigned long dirtied_before)
1418 {
1419 	int moved;
1420 	unsigned long time_expire_jif = dirtied_before;
1421 
1422 	assert_spin_locked(&wb->list_lock);
1423 	list_splice_init(&wb->b_more_io, &wb->b_io);
1424 	moved = move_expired_inodes(&wb->b_dirty, &wb->b_io, dirtied_before);
1425 	if (!work->for_sync)
1426 		time_expire_jif = jiffies - dirtytime_expire_interval * HZ;
1427 	moved += move_expired_inodes(&wb->b_dirty_time, &wb->b_io,
1428 				     time_expire_jif);
1429 	if (moved)
1430 		wb_io_lists_populated(wb);
1431 	trace_writeback_queue_io(wb, work, dirtied_before, moved);
1432 }
1433 
write_inode(struct inode * inode,struct writeback_control * wbc)1434 static int write_inode(struct inode *inode, struct writeback_control *wbc)
1435 {
1436 	int ret;
1437 
1438 	if (inode->i_sb->s_op->write_inode && !is_bad_inode(inode)) {
1439 		trace_writeback_write_inode_start(inode, wbc);
1440 		ret = inode->i_sb->s_op->write_inode(inode, wbc);
1441 		trace_writeback_write_inode(inode, wbc);
1442 		return ret;
1443 	}
1444 	return 0;
1445 }
1446 
1447 /*
1448  * Wait for writeback on an inode to complete. Called with i_lock held.
1449  * Caller must make sure inode cannot go away when we drop i_lock.
1450  */
__inode_wait_for_writeback(struct inode * inode)1451 static void __inode_wait_for_writeback(struct inode *inode)
1452 	__releases(inode->i_lock)
1453 	__acquires(inode->i_lock)
1454 {
1455 	DEFINE_WAIT_BIT(wq, &inode->i_state, __I_SYNC);
1456 	wait_queue_head_t *wqh;
1457 
1458 	wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
1459 	while (inode->i_state & I_SYNC) {
1460 		spin_unlock(&inode->i_lock);
1461 		__wait_on_bit(wqh, &wq, bit_wait,
1462 			      TASK_UNINTERRUPTIBLE);
1463 		spin_lock(&inode->i_lock);
1464 	}
1465 }
1466 
1467 /*
1468  * Wait for writeback on an inode to complete. Caller must have inode pinned.
1469  */
inode_wait_for_writeback(struct inode * inode)1470 void inode_wait_for_writeback(struct inode *inode)
1471 {
1472 	spin_lock(&inode->i_lock);
1473 	__inode_wait_for_writeback(inode);
1474 	spin_unlock(&inode->i_lock);
1475 }
1476 
1477 /*
1478  * Sleep until I_SYNC is cleared. This function must be called with i_lock
1479  * held and drops it. It is aimed for callers not holding any inode reference
1480  * so once i_lock is dropped, inode can go away.
1481  */
inode_sleep_on_writeback(struct inode * inode)1482 static void inode_sleep_on_writeback(struct inode *inode)
1483 	__releases(inode->i_lock)
1484 {
1485 	DEFINE_WAIT(wait);
1486 	wait_queue_head_t *wqh = bit_waitqueue(&inode->i_state, __I_SYNC);
1487 	int sleep;
1488 
1489 	prepare_to_wait(wqh, &wait, TASK_UNINTERRUPTIBLE);
1490 	sleep = inode->i_state & I_SYNC;
1491 	spin_unlock(&inode->i_lock);
1492 	if (sleep)
1493 		schedule();
1494 	finish_wait(wqh, &wait);
1495 }
1496 
1497 /*
1498  * Find proper writeback list for the inode depending on its current state and
1499  * possibly also change of its state while we were doing writeback.  Here we
1500  * handle things such as livelock prevention or fairness of writeback among
1501  * inodes. This function can be called only by flusher thread - noone else
1502  * processes all inodes in writeback lists and requeueing inodes behind flusher
1503  * thread's back can have unexpected consequences.
1504  */
requeue_inode(struct inode * inode,struct bdi_writeback * wb,struct writeback_control * wbc)1505 static void requeue_inode(struct inode *inode, struct bdi_writeback *wb,
1506 			  struct writeback_control *wbc)
1507 {
1508 	if (inode->i_state & I_FREEING)
1509 		return;
1510 
1511 	/*
1512 	 * Sync livelock prevention. Each inode is tagged and synced in one
1513 	 * shot. If still dirty, it will be redirty_tail()'ed below.  Update
1514 	 * the dirty time to prevent enqueue and sync it again.
1515 	 */
1516 	if ((inode->i_state & I_DIRTY) &&
1517 	    (wbc->sync_mode == WB_SYNC_ALL || wbc->tagged_writepages))
1518 		inode->dirtied_when = jiffies;
1519 
1520 	if (wbc->pages_skipped) {
1521 		/*
1522 		 * writeback is not making progress due to locked
1523 		 * buffers. Skip this inode for now.
1524 		 */
1525 		redirty_tail_locked(inode, wb);
1526 		return;
1527 	}
1528 
1529 	if (mapping_tagged(inode->i_mapping, PAGECACHE_TAG_DIRTY)) {
1530 		/*
1531 		 * We didn't write back all the pages.  nfs_writepages()
1532 		 * sometimes bales out without doing anything.
1533 		 */
1534 		if (wbc->nr_to_write <= 0) {
1535 			/* Slice used up. Queue for next turn. */
1536 			requeue_io(inode, wb);
1537 		} else {
1538 			/*
1539 			 * Writeback blocked by something other than
1540 			 * congestion. Delay the inode for some time to
1541 			 * avoid spinning on the CPU (100% iowait)
1542 			 * retrying writeback of the dirty page/inode
1543 			 * that cannot be performed immediately.
1544 			 */
1545 			redirty_tail_locked(inode, wb);
1546 		}
1547 	} else if (inode->i_state & I_DIRTY) {
1548 		/*
1549 		 * Filesystems can dirty the inode during writeback operations,
1550 		 * such as delayed allocation during submission or metadata
1551 		 * updates after data IO completion.
1552 		 */
1553 		redirty_tail_locked(inode, wb);
1554 	} else if (inode->i_state & I_DIRTY_TIME) {
1555 		inode->dirtied_when = jiffies;
1556 		inode_io_list_move_locked(inode, wb, &wb->b_dirty_time);
1557 		inode->i_state &= ~I_SYNC_QUEUED;
1558 	} else {
1559 		/* The inode is clean. Remove from writeback lists. */
1560 		inode_cgwb_move_to_attached(inode, wb);
1561 	}
1562 }
1563 
1564 /*
1565  * Write out an inode and its dirty pages (or some of its dirty pages, depending
1566  * on @wbc->nr_to_write), and clear the relevant dirty flags from i_state.
1567  *
1568  * This doesn't remove the inode from the writeback list it is on, except
1569  * potentially to move it from b_dirty_time to b_dirty due to timestamp
1570  * expiration.  The caller is otherwise responsible for writeback list handling.
1571  *
1572  * The caller is also responsible for setting the I_SYNC flag beforehand and
1573  * calling inode_sync_complete() to clear it afterwards.
1574  */
1575 static int
__writeback_single_inode(struct inode * inode,struct writeback_control * wbc)1576 __writeback_single_inode(struct inode *inode, struct writeback_control *wbc)
1577 {
1578 	struct address_space *mapping = inode->i_mapping;
1579 	long nr_to_write = wbc->nr_to_write;
1580 	unsigned dirty;
1581 	int ret;
1582 
1583 	WARN_ON(!(inode->i_state & I_SYNC));
1584 
1585 	trace_writeback_single_inode_start(inode, wbc, nr_to_write);
1586 
1587 	ret = do_writepages(mapping, wbc);
1588 
1589 	/*
1590 	 * Make sure to wait on the data before writing out the metadata.
1591 	 * This is important for filesystems that modify metadata on data
1592 	 * I/O completion. We don't do it for sync(2) writeback because it has a
1593 	 * separate, external IO completion path and ->sync_fs for guaranteeing
1594 	 * inode metadata is written back correctly.
1595 	 */
1596 	if (wbc->sync_mode == WB_SYNC_ALL && !wbc->for_sync) {
1597 		int err = filemap_fdatawait(mapping);
1598 		if (ret == 0)
1599 			ret = err;
1600 	}
1601 
1602 	/*
1603 	 * If the inode has dirty timestamps and we need to write them, call
1604 	 * mark_inode_dirty_sync() to notify the filesystem about it and to
1605 	 * change I_DIRTY_TIME into I_DIRTY_SYNC.
1606 	 */
1607 	if ((inode->i_state & I_DIRTY_TIME) &&
1608 	    (wbc->sync_mode == WB_SYNC_ALL ||
1609 	     time_after(jiffies, inode->dirtied_time_when +
1610 			dirtytime_expire_interval * HZ))) {
1611 		trace_writeback_lazytime(inode);
1612 		mark_inode_dirty_sync(inode);
1613 	}
1614 
1615 	/*
1616 	 * Get and clear the dirty flags from i_state.  This needs to be done
1617 	 * after calling writepages because some filesystems may redirty the
1618 	 * inode during writepages due to delalloc.  It also needs to be done
1619 	 * after handling timestamp expiration, as that may dirty the inode too.
1620 	 */
1621 	spin_lock(&inode->i_lock);
1622 	dirty = inode->i_state & I_DIRTY;
1623 	inode->i_state &= ~dirty;
1624 
1625 	/*
1626 	 * Paired with smp_mb() in __mark_inode_dirty().  This allows
1627 	 * __mark_inode_dirty() to test i_state without grabbing i_lock -
1628 	 * either they see the I_DIRTY bits cleared or we see the dirtied
1629 	 * inode.
1630 	 *
1631 	 * I_DIRTY_PAGES is always cleared together above even if @mapping
1632 	 * still has dirty pages.  The flag is reinstated after smp_mb() if
1633 	 * necessary.  This guarantees that either __mark_inode_dirty()
1634 	 * sees clear I_DIRTY_PAGES or we see PAGECACHE_TAG_DIRTY.
1635 	 */
1636 	smp_mb();
1637 
1638 	if (mapping_tagged(mapping, PAGECACHE_TAG_DIRTY))
1639 		inode->i_state |= I_DIRTY_PAGES;
1640 	else if (unlikely(inode->i_state & I_PINNING_FSCACHE_WB)) {
1641 		if (!(inode->i_state & I_DIRTY_PAGES)) {
1642 			inode->i_state &= ~I_PINNING_FSCACHE_WB;
1643 			wbc->unpinned_fscache_wb = true;
1644 			dirty |= I_PINNING_FSCACHE_WB; /* Cause write_inode */
1645 		}
1646 	}
1647 
1648 	spin_unlock(&inode->i_lock);
1649 
1650 	/* Don't write the inode if only I_DIRTY_PAGES was set */
1651 	if (dirty & ~I_DIRTY_PAGES) {
1652 		int err = write_inode(inode, wbc);
1653 		if (ret == 0)
1654 			ret = err;
1655 	}
1656 	wbc->unpinned_fscache_wb = false;
1657 	trace_writeback_single_inode(inode, wbc, nr_to_write);
1658 	return ret;
1659 }
1660 
1661 /*
1662  * Write out an inode's dirty data and metadata on-demand, i.e. separately from
1663  * the regular batched writeback done by the flusher threads in
1664  * writeback_sb_inodes().  @wbc controls various aspects of the write, such as
1665  * whether it is a data-integrity sync (%WB_SYNC_ALL) or not (%WB_SYNC_NONE).
1666  *
1667  * To prevent the inode from going away, either the caller must have a reference
1668  * to the inode, or the inode must have I_WILL_FREE or I_FREEING set.
1669  */
writeback_single_inode(struct inode * inode,struct writeback_control * wbc)1670 static int writeback_single_inode(struct inode *inode,
1671 				  struct writeback_control *wbc)
1672 {
1673 	struct bdi_writeback *wb;
1674 	int ret = 0;
1675 
1676 	spin_lock(&inode->i_lock);
1677 	if (!atomic_read(&inode->i_count))
1678 		WARN_ON(!(inode->i_state & (I_WILL_FREE|I_FREEING)));
1679 	else
1680 		WARN_ON(inode->i_state & I_WILL_FREE);
1681 
1682 	if (inode->i_state & I_SYNC) {
1683 		/*
1684 		 * Writeback is already running on the inode.  For WB_SYNC_NONE,
1685 		 * that's enough and we can just return.  For WB_SYNC_ALL, we
1686 		 * must wait for the existing writeback to complete, then do
1687 		 * writeback again if there's anything left.
1688 		 */
1689 		if (wbc->sync_mode != WB_SYNC_ALL)
1690 			goto out;
1691 		__inode_wait_for_writeback(inode);
1692 	}
1693 	WARN_ON(inode->i_state & I_SYNC);
1694 	/*
1695 	 * If the inode is already fully clean, then there's nothing to do.
1696 	 *
1697 	 * For data-integrity syncs we also need to check whether any pages are
1698 	 * still under writeback, e.g. due to prior WB_SYNC_NONE writeback.  If
1699 	 * there are any such pages, we'll need to wait for them.
1700 	 */
1701 	if (!(inode->i_state & I_DIRTY_ALL) &&
1702 	    (wbc->sync_mode != WB_SYNC_ALL ||
1703 	     !mapping_tagged(inode->i_mapping, PAGECACHE_TAG_WRITEBACK)))
1704 		goto out;
1705 	inode->i_state |= I_SYNC;
1706 	wbc_attach_and_unlock_inode(wbc, inode);
1707 
1708 	ret = __writeback_single_inode(inode, wbc);
1709 
1710 	wbc_detach_inode(wbc);
1711 
1712 	wb = inode_to_wb_and_lock_list(inode);
1713 	spin_lock(&inode->i_lock);
1714 	/*
1715 	 * If the inode is freeing, its i_io_list shoudn't be updated
1716 	 * as it can be finally deleted at this moment.
1717 	 */
1718 	if (!(inode->i_state & I_FREEING)) {
1719 		/*
1720 		 * If the inode is now fully clean, then it can be safely
1721 		 * removed from its writeback list (if any). Otherwise the
1722 		 * flusher threads are responsible for the writeback lists.
1723 		 */
1724 		if (!(inode->i_state & I_DIRTY_ALL))
1725 			inode_cgwb_move_to_attached(inode, wb);
1726 		else if (!(inode->i_state & I_SYNC_QUEUED)) {
1727 			if ((inode->i_state & I_DIRTY))
1728 				redirty_tail_locked(inode, wb);
1729 			else if (inode->i_state & I_DIRTY_TIME) {
1730 				inode->dirtied_when = jiffies;
1731 				inode_io_list_move_locked(inode,
1732 							  wb,
1733 							  &wb->b_dirty_time);
1734 			}
1735 		}
1736 	}
1737 
1738 	spin_unlock(&wb->list_lock);
1739 	inode_sync_complete(inode);
1740 out:
1741 	spin_unlock(&inode->i_lock);
1742 	return ret;
1743 }
1744 
writeback_chunk_size(struct bdi_writeback * wb,struct wb_writeback_work * work)1745 static long writeback_chunk_size(struct bdi_writeback *wb,
1746 				 struct wb_writeback_work *work)
1747 {
1748 	long pages;
1749 
1750 	/*
1751 	 * WB_SYNC_ALL mode does livelock avoidance by syncing dirty
1752 	 * inodes/pages in one big loop. Setting wbc.nr_to_write=LONG_MAX
1753 	 * here avoids calling into writeback_inodes_wb() more than once.
1754 	 *
1755 	 * The intended call sequence for WB_SYNC_ALL writeback is:
1756 	 *
1757 	 *      wb_writeback()
1758 	 *          writeback_sb_inodes()       <== called only once
1759 	 *              write_cache_pages()     <== called once for each inode
1760 	 *                   (quickly) tag currently dirty pages
1761 	 *                   (maybe slowly) sync all tagged pages
1762 	 */
1763 	if (work->sync_mode == WB_SYNC_ALL || work->tagged_writepages)
1764 		pages = LONG_MAX;
1765 	else {
1766 		pages = min(wb->avg_write_bandwidth / 2,
1767 			    global_wb_domain.dirty_limit / DIRTY_SCOPE);
1768 		pages = min(pages, work->nr_pages);
1769 		pages = round_down(pages + MIN_WRITEBACK_PAGES,
1770 				   MIN_WRITEBACK_PAGES);
1771 	}
1772 
1773 	return pages;
1774 }
1775 
1776 /*
1777  * Write a portion of b_io inodes which belong to @sb.
1778  *
1779  * Return the number of pages and/or inodes written.
1780  *
1781  * NOTE! This is called with wb->list_lock held, and will
1782  * unlock and relock that for each inode it ends up doing
1783  * IO for.
1784  */
writeback_sb_inodes(struct super_block * sb,struct bdi_writeback * wb,struct wb_writeback_work * work)1785 static long writeback_sb_inodes(struct super_block *sb,
1786 				struct bdi_writeback *wb,
1787 				struct wb_writeback_work *work)
1788 {
1789 	struct writeback_control wbc = {
1790 		.sync_mode		= work->sync_mode,
1791 		.tagged_writepages	= work->tagged_writepages,
1792 		.for_kupdate		= work->for_kupdate,
1793 		.for_background		= work->for_background,
1794 		.for_sync		= work->for_sync,
1795 		.range_cyclic		= work->range_cyclic,
1796 		.range_start		= 0,
1797 		.range_end		= LLONG_MAX,
1798 	};
1799 	unsigned long start_time = jiffies;
1800 	long write_chunk;
1801 	long total_wrote = 0;  /* count both pages and inodes */
1802 
1803 	while (!list_empty(&wb->b_io)) {
1804 		struct inode *inode = wb_inode(wb->b_io.prev);
1805 		struct bdi_writeback *tmp_wb;
1806 		long wrote;
1807 
1808 		if (inode->i_sb != sb) {
1809 			if (work->sb) {
1810 				/*
1811 				 * We only want to write back data for this
1812 				 * superblock, move all inodes not belonging
1813 				 * to it back onto the dirty list.
1814 				 */
1815 				redirty_tail(inode, wb);
1816 				continue;
1817 			}
1818 
1819 			/*
1820 			 * The inode belongs to a different superblock.
1821 			 * Bounce back to the caller to unpin this and
1822 			 * pin the next superblock.
1823 			 */
1824 			break;
1825 		}
1826 
1827 		/*
1828 		 * Don't bother with new inodes or inodes being freed, first
1829 		 * kind does not need periodic writeout yet, and for the latter
1830 		 * kind writeout is handled by the freer.
1831 		 */
1832 		spin_lock(&inode->i_lock);
1833 		if (inode->i_state & (I_NEW | I_FREEING | I_WILL_FREE)) {
1834 			redirty_tail_locked(inode, wb);
1835 			spin_unlock(&inode->i_lock);
1836 			continue;
1837 		}
1838 		if ((inode->i_state & I_SYNC) && wbc.sync_mode != WB_SYNC_ALL) {
1839 			/*
1840 			 * If this inode is locked for writeback and we are not
1841 			 * doing writeback-for-data-integrity, move it to
1842 			 * b_more_io so that writeback can proceed with the
1843 			 * other inodes on s_io.
1844 			 *
1845 			 * We'll have another go at writing back this inode
1846 			 * when we completed a full scan of b_io.
1847 			 */
1848 			requeue_io(inode, wb);
1849 			spin_unlock(&inode->i_lock);
1850 			trace_writeback_sb_inodes_requeue(inode);
1851 			continue;
1852 		}
1853 		spin_unlock(&wb->list_lock);
1854 
1855 		/*
1856 		 * We already requeued the inode if it had I_SYNC set and we
1857 		 * are doing WB_SYNC_NONE writeback. So this catches only the
1858 		 * WB_SYNC_ALL case.
1859 		 */
1860 		if (inode->i_state & I_SYNC) {
1861 			/* Wait for I_SYNC. This function drops i_lock... */
1862 			inode_sleep_on_writeback(inode);
1863 			/* Inode may be gone, start again */
1864 			spin_lock(&wb->list_lock);
1865 			continue;
1866 		}
1867 		inode->i_state |= I_SYNC;
1868 		wbc_attach_and_unlock_inode(&wbc, inode);
1869 
1870 		write_chunk = writeback_chunk_size(wb, work);
1871 		wbc.nr_to_write = write_chunk;
1872 		wbc.pages_skipped = 0;
1873 
1874 		/*
1875 		 * We use I_SYNC to pin the inode in memory. While it is set
1876 		 * evict_inode() will wait so the inode cannot be freed.
1877 		 */
1878 		__writeback_single_inode(inode, &wbc);
1879 
1880 		wbc_detach_inode(&wbc);
1881 		work->nr_pages -= write_chunk - wbc.nr_to_write;
1882 		wrote = write_chunk - wbc.nr_to_write - wbc.pages_skipped;
1883 		wrote = wrote < 0 ? 0 : wrote;
1884 		total_wrote += wrote;
1885 
1886 		if (need_resched()) {
1887 			/*
1888 			 * We're trying to balance between building up a nice
1889 			 * long list of IOs to improve our merge rate, and
1890 			 * getting those IOs out quickly for anyone throttling
1891 			 * in balance_dirty_pages().  cond_resched() doesn't
1892 			 * unplug, so get our IOs out the door before we
1893 			 * give up the CPU.
1894 			 */
1895 			blk_flush_plug(current->plug, false);
1896 			cond_resched();
1897 		}
1898 
1899 		/*
1900 		 * Requeue @inode if still dirty.  Be careful as @inode may
1901 		 * have been switched to another wb in the meantime.
1902 		 */
1903 		tmp_wb = inode_to_wb_and_lock_list(inode);
1904 		spin_lock(&inode->i_lock);
1905 		if (!(inode->i_state & I_DIRTY_ALL))
1906 			total_wrote++;
1907 		requeue_inode(inode, tmp_wb, &wbc);
1908 		inode_sync_complete(inode);
1909 		spin_unlock(&inode->i_lock);
1910 
1911 		if (unlikely(tmp_wb != wb)) {
1912 			spin_unlock(&tmp_wb->list_lock);
1913 			spin_lock(&wb->list_lock);
1914 		}
1915 
1916 		/*
1917 		 * bail out to wb_writeback() often enough to check
1918 		 * background threshold and other termination conditions.
1919 		 */
1920 		if (total_wrote) {
1921 			if (time_is_before_jiffies(start_time + HZ / 10UL))
1922 				break;
1923 			if (work->nr_pages <= 0)
1924 				break;
1925 		}
1926 	}
1927 	return total_wrote;
1928 }
1929 
__writeback_inodes_wb(struct bdi_writeback * wb,struct wb_writeback_work * work)1930 static long __writeback_inodes_wb(struct bdi_writeback *wb,
1931 				  struct wb_writeback_work *work)
1932 {
1933 	unsigned long start_time = jiffies;
1934 	long wrote = 0;
1935 
1936 	while (!list_empty(&wb->b_io)) {
1937 		struct inode *inode = wb_inode(wb->b_io.prev);
1938 		struct super_block *sb = inode->i_sb;
1939 
1940 		if (!trylock_super(sb)) {
1941 			/*
1942 			 * trylock_super() may fail consistently due to
1943 			 * s_umount being grabbed by someone else. Don't use
1944 			 * requeue_io() to avoid busy retrying the inode/sb.
1945 			 */
1946 			redirty_tail(inode, wb);
1947 			continue;
1948 		}
1949 		wrote += writeback_sb_inodes(sb, wb, work);
1950 		up_read(&sb->s_umount);
1951 
1952 		/* refer to the same tests at the end of writeback_sb_inodes */
1953 		if (wrote) {
1954 			if (time_is_before_jiffies(start_time + HZ / 10UL))
1955 				break;
1956 			if (work->nr_pages <= 0)
1957 				break;
1958 		}
1959 	}
1960 	/* Leave any unwritten inodes on b_io */
1961 	return wrote;
1962 }
1963 
writeback_inodes_wb(struct bdi_writeback * wb,long nr_pages,enum wb_reason reason)1964 static long writeback_inodes_wb(struct bdi_writeback *wb, long nr_pages,
1965 				enum wb_reason reason)
1966 {
1967 	struct wb_writeback_work work = {
1968 		.nr_pages	= nr_pages,
1969 		.sync_mode	= WB_SYNC_NONE,
1970 		.range_cyclic	= 1,
1971 		.reason		= reason,
1972 	};
1973 	struct blk_plug plug;
1974 
1975 	blk_start_plug(&plug);
1976 	spin_lock(&wb->list_lock);
1977 	if (list_empty(&wb->b_io))
1978 		queue_io(wb, &work, jiffies);
1979 	__writeback_inodes_wb(wb, &work);
1980 	spin_unlock(&wb->list_lock);
1981 	blk_finish_plug(&plug);
1982 
1983 	return nr_pages - work.nr_pages;
1984 }
1985 
1986 /*
1987  * Explicit flushing or periodic writeback of "old" data.
1988  *
1989  * Define "old": the first time one of an inode's pages is dirtied, we mark the
1990  * dirtying-time in the inode's address_space.  So this periodic writeback code
1991  * just walks the superblock inode list, writing back any inodes which are
1992  * older than a specific point in time.
1993  *
1994  * Try to run once per dirty_writeback_interval.  But if a writeback event
1995  * takes longer than a dirty_writeback_interval interval, then leave a
1996  * one-second gap.
1997  *
1998  * dirtied_before takes precedence over nr_to_write.  So we'll only write back
1999  * all dirty pages if they are all attached to "old" mappings.
2000  */
wb_writeback(struct bdi_writeback * wb,struct wb_writeback_work * work)2001 static long wb_writeback(struct bdi_writeback *wb,
2002 			 struct wb_writeback_work *work)
2003 {
2004 	long nr_pages = work->nr_pages;
2005 	unsigned long dirtied_before = jiffies;
2006 	struct inode *inode;
2007 	long progress;
2008 	struct blk_plug plug;
2009 
2010 	blk_start_plug(&plug);
2011 	spin_lock(&wb->list_lock);
2012 	for (;;) {
2013 		/*
2014 		 * Stop writeback when nr_pages has been consumed
2015 		 */
2016 		if (work->nr_pages <= 0)
2017 			break;
2018 
2019 		/*
2020 		 * Background writeout and kupdate-style writeback may
2021 		 * run forever. Stop them if there is other work to do
2022 		 * so that e.g. sync can proceed. They'll be restarted
2023 		 * after the other works are all done.
2024 		 */
2025 		if ((work->for_background || work->for_kupdate) &&
2026 		    !list_empty(&wb->work_list))
2027 			break;
2028 
2029 		/*
2030 		 * For background writeout, stop when we are below the
2031 		 * background dirty threshold
2032 		 */
2033 		if (work->for_background && !wb_over_bg_thresh(wb))
2034 			break;
2035 
2036 		/*
2037 		 * Kupdate and background works are special and we want to
2038 		 * include all inodes that need writing. Livelock avoidance is
2039 		 * handled by these works yielding to any other work so we are
2040 		 * safe.
2041 		 */
2042 		if (work->for_kupdate) {
2043 			dirtied_before = jiffies -
2044 				msecs_to_jiffies(dirty_expire_interval * 10);
2045 		} else if (work->for_background)
2046 			dirtied_before = jiffies;
2047 
2048 		trace_writeback_start(wb, work);
2049 		if (list_empty(&wb->b_io))
2050 			queue_io(wb, work, dirtied_before);
2051 		if (work->sb)
2052 			progress = writeback_sb_inodes(work->sb, wb, work);
2053 		else
2054 			progress = __writeback_inodes_wb(wb, work);
2055 		trace_writeback_written(wb, work);
2056 
2057 		/*
2058 		 * Did we write something? Try for more
2059 		 *
2060 		 * Dirty inodes are moved to b_io for writeback in batches.
2061 		 * The completion of the current batch does not necessarily
2062 		 * mean the overall work is done. So we keep looping as long
2063 		 * as made some progress on cleaning pages or inodes.
2064 		 */
2065 		if (progress)
2066 			continue;
2067 		/*
2068 		 * No more inodes for IO, bail
2069 		 */
2070 		if (list_empty(&wb->b_more_io))
2071 			break;
2072 		/*
2073 		 * Nothing written. Wait for some inode to
2074 		 * become available for writeback. Otherwise
2075 		 * we'll just busyloop.
2076 		 */
2077 		trace_writeback_wait(wb, work);
2078 		inode = wb_inode(wb->b_more_io.prev);
2079 		spin_lock(&inode->i_lock);
2080 		spin_unlock(&wb->list_lock);
2081 		/* This function drops i_lock... */
2082 		inode_sleep_on_writeback(inode);
2083 		spin_lock(&wb->list_lock);
2084 	}
2085 	spin_unlock(&wb->list_lock);
2086 	blk_finish_plug(&plug);
2087 
2088 	return nr_pages - work->nr_pages;
2089 }
2090 
2091 /*
2092  * Return the next wb_writeback_work struct that hasn't been processed yet.
2093  */
get_next_work_item(struct bdi_writeback * wb)2094 static struct wb_writeback_work *get_next_work_item(struct bdi_writeback *wb)
2095 {
2096 	struct wb_writeback_work *work = NULL;
2097 
2098 	spin_lock_irq(&wb->work_lock);
2099 	if (!list_empty(&wb->work_list)) {
2100 		work = list_entry(wb->work_list.next,
2101 				  struct wb_writeback_work, list);
2102 		list_del_init(&work->list);
2103 	}
2104 	spin_unlock_irq(&wb->work_lock);
2105 	return work;
2106 }
2107 
wb_check_background_flush(struct bdi_writeback * wb)2108 static long wb_check_background_flush(struct bdi_writeback *wb)
2109 {
2110 	if (wb_over_bg_thresh(wb)) {
2111 
2112 		struct wb_writeback_work work = {
2113 			.nr_pages	= LONG_MAX,
2114 			.sync_mode	= WB_SYNC_NONE,
2115 			.for_background	= 1,
2116 			.range_cyclic	= 1,
2117 			.reason		= WB_REASON_BACKGROUND,
2118 		};
2119 
2120 		return wb_writeback(wb, &work);
2121 	}
2122 
2123 	return 0;
2124 }
2125 
wb_check_old_data_flush(struct bdi_writeback * wb)2126 static long wb_check_old_data_flush(struct bdi_writeback *wb)
2127 {
2128 	unsigned long expired;
2129 	long nr_pages;
2130 
2131 	/*
2132 	 * When set to zero, disable periodic writeback
2133 	 */
2134 	if (!dirty_writeback_interval)
2135 		return 0;
2136 
2137 	expired = wb->last_old_flush +
2138 			msecs_to_jiffies(dirty_writeback_interval * 10);
2139 	if (time_before(jiffies, expired))
2140 		return 0;
2141 
2142 	wb->last_old_flush = jiffies;
2143 	nr_pages = get_nr_dirty_pages();
2144 
2145 	if (nr_pages) {
2146 		struct wb_writeback_work work = {
2147 			.nr_pages	= nr_pages,
2148 			.sync_mode	= WB_SYNC_NONE,
2149 			.for_kupdate	= 1,
2150 			.range_cyclic	= 1,
2151 			.reason		= WB_REASON_PERIODIC,
2152 		};
2153 
2154 		return wb_writeback(wb, &work);
2155 	}
2156 
2157 	return 0;
2158 }
2159 
wb_check_start_all(struct bdi_writeback * wb)2160 static long wb_check_start_all(struct bdi_writeback *wb)
2161 {
2162 	long nr_pages;
2163 
2164 	if (!test_bit(WB_start_all, &wb->state))
2165 		return 0;
2166 
2167 	nr_pages = get_nr_dirty_pages();
2168 	if (nr_pages) {
2169 		struct wb_writeback_work work = {
2170 			.nr_pages	= wb_split_bdi_pages(wb, nr_pages),
2171 			.sync_mode	= WB_SYNC_NONE,
2172 			.range_cyclic	= 1,
2173 			.reason		= wb->start_all_reason,
2174 		};
2175 
2176 		nr_pages = wb_writeback(wb, &work);
2177 	}
2178 
2179 	clear_bit(WB_start_all, &wb->state);
2180 	return nr_pages;
2181 }
2182 
2183 
2184 /*
2185  * Retrieve work items and do the writeback they describe
2186  */
wb_do_writeback(struct bdi_writeback * wb)2187 static long wb_do_writeback(struct bdi_writeback *wb)
2188 {
2189 	struct wb_writeback_work *work;
2190 	long wrote = 0;
2191 
2192 	set_bit(WB_writeback_running, &wb->state);
2193 	while ((work = get_next_work_item(wb)) != NULL) {
2194 		trace_writeback_exec(wb, work);
2195 		wrote += wb_writeback(wb, work);
2196 		finish_writeback_work(wb, work);
2197 	}
2198 
2199 	/*
2200 	 * Check for a flush-everything request
2201 	 */
2202 	wrote += wb_check_start_all(wb);
2203 
2204 	/*
2205 	 * Check for periodic writeback, kupdated() style
2206 	 */
2207 	wrote += wb_check_old_data_flush(wb);
2208 	wrote += wb_check_background_flush(wb);
2209 	clear_bit(WB_writeback_running, &wb->state);
2210 
2211 	return wrote;
2212 }
2213 
2214 /*
2215  * Handle writeback of dirty data for the device backed by this bdi. Also
2216  * reschedules periodically and does kupdated style flushing.
2217  */
wb_workfn(struct work_struct * work)2218 void wb_workfn(struct work_struct *work)
2219 {
2220 	struct bdi_writeback *wb = container_of(to_delayed_work(work),
2221 						struct bdi_writeback, dwork);
2222 	long pages_written;
2223 
2224 	set_worker_desc("flush-%s", bdi_dev_name(wb->bdi));
2225 
2226 	if (likely(!current_is_workqueue_rescuer() ||
2227 		   !test_bit(WB_registered, &wb->state))) {
2228 		/*
2229 		 * The normal path.  Keep writing back @wb until its
2230 		 * work_list is empty.  Note that this path is also taken
2231 		 * if @wb is shutting down even when we're running off the
2232 		 * rescuer as work_list needs to be drained.
2233 		 */
2234 		do {
2235 			pages_written = wb_do_writeback(wb);
2236 			trace_writeback_pages_written(pages_written);
2237 		} while (!list_empty(&wb->work_list));
2238 	} else {
2239 		/*
2240 		 * bdi_wq can't get enough workers and we're running off
2241 		 * the emergency worker.  Don't hog it.  Hopefully, 1024 is
2242 		 * enough for efficient IO.
2243 		 */
2244 		pages_written = writeback_inodes_wb(wb, 1024,
2245 						    WB_REASON_FORKER_THREAD);
2246 		trace_writeback_pages_written(pages_written);
2247 	}
2248 
2249 	if (!list_empty(&wb->work_list))
2250 		wb_wakeup(wb);
2251 	else if (wb_has_dirty_io(wb) && dirty_writeback_interval)
2252 		wb_wakeup_delayed(wb);
2253 }
2254 
2255 /*
2256  * Start writeback of `nr_pages' pages on this bdi. If `nr_pages' is zero,
2257  * write back the whole world.
2258  */
__wakeup_flusher_threads_bdi(struct backing_dev_info * bdi,enum wb_reason reason)2259 static void __wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
2260 					 enum wb_reason reason)
2261 {
2262 	struct bdi_writeback *wb;
2263 
2264 	if (!bdi_has_dirty_io(bdi))
2265 		return;
2266 
2267 	list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node)
2268 		wb_start_writeback(wb, reason);
2269 }
2270 
wakeup_flusher_threads_bdi(struct backing_dev_info * bdi,enum wb_reason reason)2271 void wakeup_flusher_threads_bdi(struct backing_dev_info *bdi,
2272 				enum wb_reason reason)
2273 {
2274 	rcu_read_lock();
2275 	__wakeup_flusher_threads_bdi(bdi, reason);
2276 	rcu_read_unlock();
2277 }
2278 
2279 /*
2280  * Wakeup the flusher threads to start writeback of all currently dirty pages
2281  */
wakeup_flusher_threads(enum wb_reason reason)2282 void wakeup_flusher_threads(enum wb_reason reason)
2283 {
2284 	struct backing_dev_info *bdi;
2285 
2286 	/*
2287 	 * If we are expecting writeback progress we must submit plugged IO.
2288 	 */
2289 	blk_flush_plug(current->plug, true);
2290 
2291 	rcu_read_lock();
2292 	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list)
2293 		__wakeup_flusher_threads_bdi(bdi, reason);
2294 	rcu_read_unlock();
2295 }
2296 
2297 /*
2298  * Wake up bdi's periodically to make sure dirtytime inodes gets
2299  * written back periodically.  We deliberately do *not* check the
2300  * b_dirtytime list in wb_has_dirty_io(), since this would cause the
2301  * kernel to be constantly waking up once there are any dirtytime
2302  * inodes on the system.  So instead we define a separate delayed work
2303  * function which gets called much more rarely.  (By default, only
2304  * once every 12 hours.)
2305  *
2306  * If there is any other write activity going on in the file system,
2307  * this function won't be necessary.  But if the only thing that has
2308  * happened on the file system is a dirtytime inode caused by an atime
2309  * update, we need this infrastructure below to make sure that inode
2310  * eventually gets pushed out to disk.
2311  */
2312 static void wakeup_dirtytime_writeback(struct work_struct *w);
2313 static DECLARE_DELAYED_WORK(dirtytime_work, wakeup_dirtytime_writeback);
2314 
wakeup_dirtytime_writeback(struct work_struct * w)2315 static void wakeup_dirtytime_writeback(struct work_struct *w)
2316 {
2317 	struct backing_dev_info *bdi;
2318 
2319 	rcu_read_lock();
2320 	list_for_each_entry_rcu(bdi, &bdi_list, bdi_list) {
2321 		struct bdi_writeback *wb;
2322 
2323 		list_for_each_entry_rcu(wb, &bdi->wb_list, bdi_node)
2324 			if (!list_empty(&wb->b_dirty_time))
2325 				wb_wakeup(wb);
2326 	}
2327 	rcu_read_unlock();
2328 	schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
2329 }
2330 
start_dirtytime_writeback(void)2331 static int __init start_dirtytime_writeback(void)
2332 {
2333 	schedule_delayed_work(&dirtytime_work, dirtytime_expire_interval * HZ);
2334 	return 0;
2335 }
2336 __initcall(start_dirtytime_writeback);
2337 
dirtytime_interval_handler(struct ctl_table * table,int write,void * buffer,size_t * lenp,loff_t * ppos)2338 int dirtytime_interval_handler(struct ctl_table *table, int write,
2339 			       void *buffer, size_t *lenp, loff_t *ppos)
2340 {
2341 	int ret;
2342 
2343 	ret = proc_dointvec_minmax(table, write, buffer, lenp, ppos);
2344 	if (ret == 0 && write)
2345 		mod_delayed_work(system_wq, &dirtytime_work, 0);
2346 	return ret;
2347 }
2348 
2349 /**
2350  * __mark_inode_dirty -	internal function to mark an inode dirty
2351  *
2352  * @inode: inode to mark
2353  * @flags: what kind of dirty, e.g. I_DIRTY_SYNC.  This can be a combination of
2354  *	   multiple I_DIRTY_* flags, except that I_DIRTY_TIME can't be combined
2355  *	   with I_DIRTY_PAGES.
2356  *
2357  * Mark an inode as dirty.  We notify the filesystem, then update the inode's
2358  * dirty flags.  Then, if needed we add the inode to the appropriate dirty list.
2359  *
2360  * Most callers should use mark_inode_dirty() or mark_inode_dirty_sync()
2361  * instead of calling this directly.
2362  *
2363  * CAREFUL!  We only add the inode to the dirty list if it is hashed or if it
2364  * refers to a blockdev.  Unhashed inodes will never be added to the dirty list
2365  * even if they are later hashed, as they will have been marked dirty already.
2366  *
2367  * In short, ensure you hash any inodes _before_ you start marking them dirty.
2368  *
2369  * Note that for blockdevs, inode->dirtied_when represents the dirtying time of
2370  * the block-special inode (/dev/hda1) itself.  And the ->dirtied_when field of
2371  * the kernel-internal blockdev inode represents the dirtying time of the
2372  * blockdev's pages.  This is why for I_DIRTY_PAGES we always use
2373  * page->mapping->host, so the page-dirtying time is recorded in the internal
2374  * blockdev inode.
2375  */
__mark_inode_dirty(struct inode * inode,int flags)2376 void __mark_inode_dirty(struct inode *inode, int flags)
2377 {
2378 	struct super_block *sb = inode->i_sb;
2379 	int dirtytime = 0;
2380 	struct bdi_writeback *wb = NULL;
2381 
2382 	trace_writeback_mark_inode_dirty(inode, flags);
2383 
2384 	if (flags & I_DIRTY_INODE) {
2385 		/*
2386 		 * Inode timestamp update will piggback on this dirtying.
2387 		 * We tell ->dirty_inode callback that timestamps need to
2388 		 * be updated by setting I_DIRTY_TIME in flags.
2389 		 */
2390 		if (inode->i_state & I_DIRTY_TIME) {
2391 			spin_lock(&inode->i_lock);
2392 			if (inode->i_state & I_DIRTY_TIME) {
2393 				inode->i_state &= ~I_DIRTY_TIME;
2394 				flags |= I_DIRTY_TIME;
2395 			}
2396 			spin_unlock(&inode->i_lock);
2397 		}
2398 
2399 		/*
2400 		 * Notify the filesystem about the inode being dirtied, so that
2401 		 * (if needed) it can update on-disk fields and journal the
2402 		 * inode.  This is only needed when the inode itself is being
2403 		 * dirtied now.  I.e. it's only needed for I_DIRTY_INODE, not
2404 		 * for just I_DIRTY_PAGES or I_DIRTY_TIME.
2405 		 */
2406 		trace_writeback_dirty_inode_start(inode, flags);
2407 		if (sb->s_op->dirty_inode)
2408 			sb->s_op->dirty_inode(inode,
2409 				flags & (I_DIRTY_INODE | I_DIRTY_TIME));
2410 		trace_writeback_dirty_inode(inode, flags);
2411 
2412 		/* I_DIRTY_INODE supersedes I_DIRTY_TIME. */
2413 		flags &= ~I_DIRTY_TIME;
2414 	} else {
2415 		/*
2416 		 * Else it's either I_DIRTY_PAGES, I_DIRTY_TIME, or nothing.
2417 		 * (We don't support setting both I_DIRTY_PAGES and I_DIRTY_TIME
2418 		 * in one call to __mark_inode_dirty().)
2419 		 */
2420 		dirtytime = flags & I_DIRTY_TIME;
2421 		WARN_ON_ONCE(dirtytime && flags != I_DIRTY_TIME);
2422 	}
2423 
2424 	/*
2425 	 * Paired with smp_mb() in __writeback_single_inode() for the
2426 	 * following lockless i_state test.  See there for details.
2427 	 */
2428 	smp_mb();
2429 
2430 	if ((inode->i_state & flags) == flags)
2431 		return;
2432 
2433 	spin_lock(&inode->i_lock);
2434 	if ((inode->i_state & flags) != flags) {
2435 		const int was_dirty = inode->i_state & I_DIRTY;
2436 
2437 		inode_attach_wb(inode, NULL);
2438 
2439 		inode->i_state |= flags;
2440 
2441 		/*
2442 		 * Grab inode's wb early because it requires dropping i_lock and we
2443 		 * need to make sure following checks happen atomically with dirty
2444 		 * list handling so that we don't move inodes under flush worker's
2445 		 * hands.
2446 		 */
2447 		if (!was_dirty) {
2448 			wb = locked_inode_to_wb_and_lock_list(inode);
2449 			spin_lock(&inode->i_lock);
2450 		}
2451 
2452 		/*
2453 		 * If the inode is queued for writeback by flush worker, just
2454 		 * update its dirty state. Once the flush worker is done with
2455 		 * the inode it will place it on the appropriate superblock
2456 		 * list, based upon its state.
2457 		 */
2458 		if (inode->i_state & I_SYNC_QUEUED)
2459 			goto out_unlock;
2460 
2461 		/*
2462 		 * Only add valid (hashed) inodes to the superblock's
2463 		 * dirty list.  Add blockdev inodes as well.
2464 		 */
2465 		if (!S_ISBLK(inode->i_mode)) {
2466 			if (inode_unhashed(inode))
2467 				goto out_unlock;
2468 		}
2469 		if (inode->i_state & I_FREEING)
2470 			goto out_unlock;
2471 
2472 		/*
2473 		 * If the inode was already on b_dirty/b_io/b_more_io, don't
2474 		 * reposition it (that would break b_dirty time-ordering).
2475 		 */
2476 		if (!was_dirty) {
2477 			struct list_head *dirty_list;
2478 			bool wakeup_bdi = false;
2479 
2480 			inode->dirtied_when = jiffies;
2481 			if (dirtytime)
2482 				inode->dirtied_time_when = jiffies;
2483 
2484 			if (inode->i_state & I_DIRTY)
2485 				dirty_list = &wb->b_dirty;
2486 			else
2487 				dirty_list = &wb->b_dirty_time;
2488 
2489 			wakeup_bdi = inode_io_list_move_locked(inode, wb,
2490 							       dirty_list);
2491 
2492 			spin_unlock(&wb->list_lock);
2493 			spin_unlock(&inode->i_lock);
2494 			trace_writeback_dirty_inode_enqueue(inode);
2495 
2496 			/*
2497 			 * If this is the first dirty inode for this bdi,
2498 			 * we have to wake-up the corresponding bdi thread
2499 			 * to make sure background write-back happens
2500 			 * later.
2501 			 */
2502 			if (wakeup_bdi &&
2503 			    (wb->bdi->capabilities & BDI_CAP_WRITEBACK))
2504 				wb_wakeup_delayed(wb);
2505 			return;
2506 		}
2507 	}
2508 out_unlock:
2509 	if (wb)
2510 		spin_unlock(&wb->list_lock);
2511 	spin_unlock(&inode->i_lock);
2512 }
2513 EXPORT_SYMBOL(__mark_inode_dirty);
2514 
2515 /*
2516  * The @s_sync_lock is used to serialise concurrent sync operations
2517  * to avoid lock contention problems with concurrent wait_sb_inodes() calls.
2518  * Concurrent callers will block on the s_sync_lock rather than doing contending
2519  * walks. The queueing maintains sync(2) required behaviour as all the IO that
2520  * has been issued up to the time this function is enter is guaranteed to be
2521  * completed by the time we have gained the lock and waited for all IO that is
2522  * in progress regardless of the order callers are granted the lock.
2523  */
wait_sb_inodes(struct super_block * sb)2524 static void wait_sb_inodes(struct super_block *sb)
2525 {
2526 	LIST_HEAD(sync_list);
2527 
2528 	/*
2529 	 * We need to be protected against the filesystem going from
2530 	 * r/o to r/w or vice versa.
2531 	 */
2532 	WARN_ON(!rwsem_is_locked(&sb->s_umount));
2533 
2534 	mutex_lock(&sb->s_sync_lock);
2535 
2536 	/*
2537 	 * Splice the writeback list onto a temporary list to avoid waiting on
2538 	 * inodes that have started writeback after this point.
2539 	 *
2540 	 * Use rcu_read_lock() to keep the inodes around until we have a
2541 	 * reference. s_inode_wblist_lock protects sb->s_inodes_wb as well as
2542 	 * the local list because inodes can be dropped from either by writeback
2543 	 * completion.
2544 	 */
2545 	rcu_read_lock();
2546 	spin_lock_irq(&sb->s_inode_wblist_lock);
2547 	list_splice_init(&sb->s_inodes_wb, &sync_list);
2548 
2549 	/*
2550 	 * Data integrity sync. Must wait for all pages under writeback, because
2551 	 * there may have been pages dirtied before our sync call, but which had
2552 	 * writeout started before we write it out.  In which case, the inode
2553 	 * may not be on the dirty list, but we still have to wait for that
2554 	 * writeout.
2555 	 */
2556 	while (!list_empty(&sync_list)) {
2557 		struct inode *inode = list_first_entry(&sync_list, struct inode,
2558 						       i_wb_list);
2559 		struct address_space *mapping = inode->i_mapping;
2560 
2561 		/*
2562 		 * Move each inode back to the wb list before we drop the lock
2563 		 * to preserve consistency between i_wb_list and the mapping
2564 		 * writeback tag. Writeback completion is responsible to remove
2565 		 * the inode from either list once the writeback tag is cleared.
2566 		 */
2567 		list_move_tail(&inode->i_wb_list, &sb->s_inodes_wb);
2568 
2569 		/*
2570 		 * The mapping can appear untagged while still on-list since we
2571 		 * do not have the mapping lock. Skip it here, wb completion
2572 		 * will remove it.
2573 		 */
2574 		if (!mapping_tagged(mapping, PAGECACHE_TAG_WRITEBACK))
2575 			continue;
2576 
2577 		spin_unlock_irq(&sb->s_inode_wblist_lock);
2578 
2579 		spin_lock(&inode->i_lock);
2580 		if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) {
2581 			spin_unlock(&inode->i_lock);
2582 
2583 			spin_lock_irq(&sb->s_inode_wblist_lock);
2584 			continue;
2585 		}
2586 		__iget(inode);
2587 		spin_unlock(&inode->i_lock);
2588 		rcu_read_unlock();
2589 
2590 		/*
2591 		 * We keep the error status of individual mapping so that
2592 		 * applications can catch the writeback error using fsync(2).
2593 		 * See filemap_fdatawait_keep_errors() for details.
2594 		 */
2595 		filemap_fdatawait_keep_errors(mapping);
2596 
2597 		cond_resched();
2598 
2599 		iput(inode);
2600 
2601 		rcu_read_lock();
2602 		spin_lock_irq(&sb->s_inode_wblist_lock);
2603 	}
2604 	spin_unlock_irq(&sb->s_inode_wblist_lock);
2605 	rcu_read_unlock();
2606 	mutex_unlock(&sb->s_sync_lock);
2607 }
2608 
__writeback_inodes_sb_nr(struct super_block * sb,unsigned long nr,enum wb_reason reason,bool skip_if_busy)2609 static void __writeback_inodes_sb_nr(struct super_block *sb, unsigned long nr,
2610 				     enum wb_reason reason, bool skip_if_busy)
2611 {
2612 	struct backing_dev_info *bdi = sb->s_bdi;
2613 	DEFINE_WB_COMPLETION(done, bdi);
2614 	struct wb_writeback_work work = {
2615 		.sb			= sb,
2616 		.sync_mode		= WB_SYNC_NONE,
2617 		.tagged_writepages	= 1,
2618 		.done			= &done,
2619 		.nr_pages		= nr,
2620 		.reason			= reason,
2621 	};
2622 
2623 	if (!bdi_has_dirty_io(bdi) || bdi == &noop_backing_dev_info)
2624 		return;
2625 	WARN_ON(!rwsem_is_locked(&sb->s_umount));
2626 
2627 	bdi_split_work_to_wbs(sb->s_bdi, &work, skip_if_busy);
2628 	wb_wait_for_completion(&done);
2629 }
2630 
2631 /**
2632  * writeback_inodes_sb_nr -	writeback dirty inodes from given super_block
2633  * @sb: the superblock
2634  * @nr: the number of pages to write
2635  * @reason: reason why some writeback work initiated
2636  *
2637  * Start writeback on some inodes on this super_block. No guarantees are made
2638  * on how many (if any) will be written, and this function does not wait
2639  * for IO completion of submitted IO.
2640  */
writeback_inodes_sb_nr(struct super_block * sb,unsigned long nr,enum wb_reason reason)2641 void writeback_inodes_sb_nr(struct super_block *sb,
2642 			    unsigned long nr,
2643 			    enum wb_reason reason)
2644 {
2645 	__writeback_inodes_sb_nr(sb, nr, reason, false);
2646 }
2647 EXPORT_SYMBOL(writeback_inodes_sb_nr);
2648 
2649 /**
2650  * writeback_inodes_sb	-	writeback dirty inodes from given super_block
2651  * @sb: the superblock
2652  * @reason: reason why some writeback work was initiated
2653  *
2654  * Start writeback on some inodes on this super_block. No guarantees are made
2655  * on how many (if any) will be written, and this function does not wait
2656  * for IO completion of submitted IO.
2657  */
writeback_inodes_sb(struct super_block * sb,enum wb_reason reason)2658 void writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
2659 {
2660 	return writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason);
2661 }
2662 EXPORT_SYMBOL(writeback_inodes_sb);
2663 
2664 /**
2665  * try_to_writeback_inodes_sb - try to start writeback if none underway
2666  * @sb: the superblock
2667  * @reason: reason why some writeback work was initiated
2668  *
2669  * Invoke __writeback_inodes_sb_nr if no writeback is currently underway.
2670  */
try_to_writeback_inodes_sb(struct super_block * sb,enum wb_reason reason)2671 void try_to_writeback_inodes_sb(struct super_block *sb, enum wb_reason reason)
2672 {
2673 	if (!down_read_trylock(&sb->s_umount))
2674 		return;
2675 
2676 	__writeback_inodes_sb_nr(sb, get_nr_dirty_pages(), reason, true);
2677 	up_read(&sb->s_umount);
2678 }
2679 EXPORT_SYMBOL(try_to_writeback_inodes_sb);
2680 
2681 /**
2682  * sync_inodes_sb	-	sync sb inode pages
2683  * @sb: the superblock
2684  *
2685  * This function writes and waits on any dirty inode belonging to this
2686  * super_block.
2687  */
sync_inodes_sb(struct super_block * sb)2688 void sync_inodes_sb(struct super_block *sb)
2689 {
2690 	struct backing_dev_info *bdi = sb->s_bdi;
2691 	DEFINE_WB_COMPLETION(done, bdi);
2692 	struct wb_writeback_work work = {
2693 		.sb		= sb,
2694 		.sync_mode	= WB_SYNC_ALL,
2695 		.nr_pages	= LONG_MAX,
2696 		.range_cyclic	= 0,
2697 		.done		= &done,
2698 		.reason		= WB_REASON_SYNC,
2699 		.for_sync	= 1,
2700 	};
2701 
2702 	/*
2703 	 * Can't skip on !bdi_has_dirty() because we should wait for !dirty
2704 	 * inodes under writeback and I_DIRTY_TIME inodes ignored by
2705 	 * bdi_has_dirty() need to be written out too.
2706 	 */
2707 	if (bdi == &noop_backing_dev_info)
2708 		return;
2709 	WARN_ON(!rwsem_is_locked(&sb->s_umount));
2710 
2711 	/* protect against inode wb switch, see inode_switch_wbs_work_fn() */
2712 	bdi_down_write_wb_switch_rwsem(bdi);
2713 	bdi_split_work_to_wbs(bdi, &work, false);
2714 	wb_wait_for_completion(&done);
2715 	bdi_up_write_wb_switch_rwsem(bdi);
2716 
2717 	wait_sb_inodes(sb);
2718 }
2719 EXPORT_SYMBOL(sync_inodes_sb);
2720 
2721 /**
2722  * write_inode_now	-	write an inode to disk
2723  * @inode: inode to write to disk
2724  * @sync: whether the write should be synchronous or not
2725  *
2726  * This function commits an inode to disk immediately if it is dirty. This is
2727  * primarily needed by knfsd.
2728  *
2729  * The caller must either have a ref on the inode or must have set I_WILL_FREE.
2730  */
write_inode_now(struct inode * inode,int sync)2731 int write_inode_now(struct inode *inode, int sync)
2732 {
2733 	struct writeback_control wbc = {
2734 		.nr_to_write = LONG_MAX,
2735 		.sync_mode = sync ? WB_SYNC_ALL : WB_SYNC_NONE,
2736 		.range_start = 0,
2737 		.range_end = LLONG_MAX,
2738 	};
2739 
2740 	if (!mapping_can_writeback(inode->i_mapping))
2741 		wbc.nr_to_write = 0;
2742 
2743 	might_sleep();
2744 	return writeback_single_inode(inode, &wbc);
2745 }
2746 EXPORT_SYMBOL(write_inode_now);
2747 
2748 /**
2749  * sync_inode_metadata - write an inode to disk
2750  * @inode: the inode to sync
2751  * @wait: wait for I/O to complete.
2752  *
2753  * Write an inode to disk and adjust its dirty state after completion.
2754  *
2755  * Note: only writes the actual inode, no associated data or other metadata.
2756  */
sync_inode_metadata(struct inode * inode,int wait)2757 int sync_inode_metadata(struct inode *inode, int wait)
2758 {
2759 	struct writeback_control wbc = {
2760 		.sync_mode = wait ? WB_SYNC_ALL : WB_SYNC_NONE,
2761 		.nr_to_write = 0, /* metadata-only */
2762 	};
2763 
2764 	return writeback_single_inode(inode, &wbc);
2765 }
2766 EXPORT_SYMBOL(sync_inode_metadata);
2767