1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * Functions related to interrupt-poll handling in the block layer. This
4  * is similar to NAPI for network devices.
5  */
6 #include <linux/kernel.h>
7 #include <linux/module.h>
8 #include <linux/init.h>
9 #include <linux/bio.h>
10 #include <linux/interrupt.h>
11 #include <linux/cpu.h>
12 #include <linux/irq_poll.h>
13 #include <linux/delay.h>
14 
15 static unsigned int irq_poll_budget __read_mostly = 256;
16 
17 static DEFINE_PER_CPU(struct list_head, blk_cpu_iopoll);
18 
19 /**
20  * irq_poll_sched - Schedule a run of the iopoll handler
21  * @iop:      The parent iopoll structure
22  *
23  * Description:
24  *     Add this irq_poll structure to the pending poll list and trigger the
25  *     raise of the blk iopoll softirq.
26  **/
irq_poll_sched(struct irq_poll * iop)27 void irq_poll_sched(struct irq_poll *iop)
28 {
29 	unsigned long flags;
30 
31 	if (test_bit(IRQ_POLL_F_DISABLE, &iop->state))
32 		return;
33 	if (test_and_set_bit(IRQ_POLL_F_SCHED, &iop->state))
34 		return;
35 
36 	local_irq_save(flags);
37 	list_add_tail(&iop->list, this_cpu_ptr(&blk_cpu_iopoll));
38 	raise_softirq_irqoff(IRQ_POLL_SOFTIRQ);
39 	local_irq_restore(flags);
40 }
41 EXPORT_SYMBOL(irq_poll_sched);
42 
43 /**
44  * __irq_poll_complete - Mark this @iop as un-polled again
45  * @iop:      The parent iopoll structure
46  *
47  * Description:
48  *     See irq_poll_complete(). This function must be called with interrupts
49  *     disabled.
50  **/
__irq_poll_complete(struct irq_poll * iop)51 static void __irq_poll_complete(struct irq_poll *iop)
52 {
53 	list_del(&iop->list);
54 	smp_mb__before_atomic();
55 	clear_bit_unlock(IRQ_POLL_F_SCHED, &iop->state);
56 }
57 
58 /**
59  * irq_poll_complete - Mark this @iop as un-polled again
60  * @iop:      The parent iopoll structure
61  *
62  * Description:
63  *     If a driver consumes less than the assigned budget in its run of the
64  *     iopoll handler, it'll end the polled mode by calling this function. The
65  *     iopoll handler will not be invoked again before irq_poll_sched()
66  *     is called.
67  **/
irq_poll_complete(struct irq_poll * iop)68 void irq_poll_complete(struct irq_poll *iop)
69 {
70 	unsigned long flags;
71 
72 	local_irq_save(flags);
73 	__irq_poll_complete(iop);
74 	local_irq_restore(flags);
75 }
76 EXPORT_SYMBOL(irq_poll_complete);
77 
irq_poll_softirq(struct softirq_action * h)78 static void __latent_entropy irq_poll_softirq(struct softirq_action *h)
79 {
80 	struct list_head *list = this_cpu_ptr(&blk_cpu_iopoll);
81 	int rearm = 0, budget = irq_poll_budget;
82 	unsigned long start_time = jiffies;
83 
84 	local_irq_disable();
85 
86 	while (!list_empty(list)) {
87 		struct irq_poll *iop;
88 		int work, weight;
89 
90 		/*
91 		 * If softirq window is exhausted then punt.
92 		 */
93 		if (budget <= 0 || time_after(jiffies, start_time)) {
94 			rearm = 1;
95 			break;
96 		}
97 
98 		local_irq_enable();
99 
100 		/* Even though interrupts have been re-enabled, this
101 		 * access is safe because interrupts can only add new
102 		 * entries to the tail of this list, and only ->poll()
103 		 * calls can remove this head entry from the list.
104 		 */
105 		iop = list_entry(list->next, struct irq_poll, list);
106 
107 		weight = iop->weight;
108 		work = 0;
109 		if (test_bit(IRQ_POLL_F_SCHED, &iop->state))
110 			work = iop->poll(iop, weight);
111 
112 		budget -= work;
113 
114 		local_irq_disable();
115 
116 		/*
117 		 * Drivers must not modify the iopoll state, if they
118 		 * consume their assigned weight (or more, some drivers can't
119 		 * easily just stop processing, they have to complete an
120 		 * entire mask of commands).In such cases this code
121 		 * still "owns" the iopoll instance and therefore can
122 		 * move the instance around on the list at-will.
123 		 */
124 		if (work >= weight) {
125 			if (test_bit(IRQ_POLL_F_DISABLE, &iop->state))
126 				__irq_poll_complete(iop);
127 			else
128 				list_move_tail(&iop->list, list);
129 		}
130 	}
131 
132 	if (rearm)
133 		__raise_softirq_irqoff(IRQ_POLL_SOFTIRQ);
134 
135 	local_irq_enable();
136 }
137 
138 /**
139  * irq_poll_disable - Disable iopoll on this @iop
140  * @iop:      The parent iopoll structure
141  *
142  * Description:
143  *     Disable io polling and wait for any pending callbacks to have completed.
144  **/
irq_poll_disable(struct irq_poll * iop)145 void irq_poll_disable(struct irq_poll *iop)
146 {
147 	set_bit(IRQ_POLL_F_DISABLE, &iop->state);
148 	while (test_and_set_bit(IRQ_POLL_F_SCHED, &iop->state))
149 		msleep(1);
150 	clear_bit(IRQ_POLL_F_DISABLE, &iop->state);
151 }
152 EXPORT_SYMBOL(irq_poll_disable);
153 
154 /**
155  * irq_poll_enable - Enable iopoll on this @iop
156  * @iop:      The parent iopoll structure
157  *
158  * Description:
159  *     Enable iopoll on this @iop. Note that the handler run will not be
160  *     scheduled, it will only mark it as active.
161  **/
irq_poll_enable(struct irq_poll * iop)162 void irq_poll_enable(struct irq_poll *iop)
163 {
164 	BUG_ON(!test_bit(IRQ_POLL_F_SCHED, &iop->state));
165 	smp_mb__before_atomic();
166 	clear_bit_unlock(IRQ_POLL_F_SCHED, &iop->state);
167 }
168 EXPORT_SYMBOL(irq_poll_enable);
169 
170 /**
171  * irq_poll_init - Initialize this @iop
172  * @iop:      The parent iopoll structure
173  * @weight:   The default weight (or command completion budget)
174  * @poll_fn:  The handler to invoke
175  *
176  * Description:
177  *     Initialize and enable this irq_poll structure.
178  **/
irq_poll_init(struct irq_poll * iop,int weight,irq_poll_fn * poll_fn)179 void irq_poll_init(struct irq_poll *iop, int weight, irq_poll_fn *poll_fn)
180 {
181 	memset(iop, 0, sizeof(*iop));
182 	INIT_LIST_HEAD(&iop->list);
183 	iop->weight = weight;
184 	iop->poll = poll_fn;
185 }
186 EXPORT_SYMBOL(irq_poll_init);
187 
irq_poll_cpu_dead(unsigned int cpu)188 static int irq_poll_cpu_dead(unsigned int cpu)
189 {
190 	/*
191 	 * If a CPU goes away, splice its entries to the current CPU and
192 	 * set the POLL softirq bit. The local_bh_disable()/enable() pair
193 	 * ensures that it is handled. Otherwise the current CPU could
194 	 * reach idle with the POLL softirq pending.
195 	 */
196 	local_bh_disable();
197 	local_irq_disable();
198 	list_splice_init(&per_cpu(blk_cpu_iopoll, cpu),
199 			 this_cpu_ptr(&blk_cpu_iopoll));
200 	__raise_softirq_irqoff(IRQ_POLL_SOFTIRQ);
201 	local_irq_enable();
202 	local_bh_enable();
203 
204 	return 0;
205 }
206 
irq_poll_setup(void)207 static __init int irq_poll_setup(void)
208 {
209 	int i;
210 
211 	for_each_possible_cpu(i)
212 		INIT_LIST_HEAD(&per_cpu(blk_cpu_iopoll, i));
213 
214 	open_softirq(IRQ_POLL_SOFTIRQ, irq_poll_softirq);
215 	cpuhp_setup_state_nocalls(CPUHP_IRQ_POLL_DEAD, "irq_poll:dead", NULL,
216 				  irq_poll_cpu_dead);
217 	return 0;
218 }
219 subsys_initcall(irq_poll_setup);
220