1// SPDX-License-Identifier: GPL-2.0
  2/*
  3 * Functions related to softirq rq completions
  4 */
  5#include <linux/kernel.h>
  6#include <linux/module.h>
  7#include <linux/init.h>
  8#include <linux/bio.h>
  9#include <linux/blkdev.h>
 10#include <linux/interrupt.h>
 11#include <linux/cpu.h>
 12#include <linux/sched.h>
 13#include <linux/sched/topology.h>
 14
 15#include "blk.h"
 16
 17static DEFINE_PER_CPU(struct list_head, blk_cpu_done);
 18
 19/*
 20 * Softirq action handler - move entries to local list and loop over them
 21 * while passing them to the queue registered handler.
 22 */
 23static __latent_entropy void blk_done_softirq(struct softirq_action *h)
 24{
 25	struct list_head *cpu_list, local_list;
 26
 27	local_irq_disable();
 28	cpu_list = this_cpu_ptr(&blk_cpu_done);
 29	list_replace_init(cpu_list, &local_list);
 30	local_irq_enable();
 31
 32	while (!list_empty(&local_list)) {
 33		struct request *rq;
 34
 35		rq = list_entry(local_list.next, struct request, ipi_list);
 36		list_del_init(&rq->ipi_list);
 37		rq->q->softirq_done_fn(rq);
 38	}
 39}
 40
 41#ifdef CONFIG_SMP
 42static void trigger_softirq(void *data)
 43{
 44	struct request *rq = data;
 45	unsigned long flags;
 46	struct list_head *list;
 47
 48	local_irq_save(flags);
 49	list = this_cpu_ptr(&blk_cpu_done);
 50	list_add_tail(&rq->ipi_list, list);
 51
 52	if (list->next == &rq->ipi_list)
 53		raise_softirq_irqoff(BLOCK_SOFTIRQ);
 54
 55	local_irq_restore(flags);
 56}
 57
 58/*
 59 * Setup and invoke a run of 'trigger_softirq' on the given cpu.
 60 */
 61static int raise_blk_irq(int cpu, struct request *rq)
 62{
 63	if (cpu_online(cpu)) {
 64		call_single_data_t *data = &rq->csd;
 65
 66		data->func = trigger_softirq;
 67		data->info = rq;
 68		data->flags = 0;
 69
 70		smp_call_function_single_async(cpu, data);
 71		return 0;
 72	}
 73
 74	return 1;
 75}
 76#else /* CONFIG_SMP */
 77static int raise_blk_irq(int cpu, struct request *rq)
 78{
 79	return 1;
 80}
 81#endif
 82
 83static int blk_softirq_cpu_dead(unsigned int cpu)
 84{
 85	/*
 86	 * If a CPU goes away, splice its entries to the current CPU
 87	 * and trigger a run of the softirq
 88	 */
 89	local_irq_disable();
 90	list_splice_init(&per_cpu(blk_cpu_done, cpu),
 91			 this_cpu_ptr(&blk_cpu_done));
 92	raise_softirq_irqoff(BLOCK_SOFTIRQ);
 93	local_irq_enable();
 94
 95	return 0;
 96}
 97
 98void __blk_complete_request(struct request *req)
 99{
100	int ccpu, cpu;
101	struct request_queue *q = req->q;
102	unsigned long flags;
103	bool shared = false;
104
105	BUG_ON(!q->softirq_done_fn);
106
107	local_irq_save(flags);
108	cpu = smp_processor_id();
109
110	/*
111	 * Select completion CPU
112	 */
113	if (req->cpu != -1) {
114		ccpu = req->cpu;
115		if (!test_bit(QUEUE_FLAG_SAME_FORCE, &q->queue_flags))
116			shared = cpus_share_cache(cpu, ccpu);
117	} else
118		ccpu = cpu;
119
120	/*
121	 * If current CPU and requested CPU share a cache, run the softirq on
122	 * the current CPU. One might concern this is just like
123	 * QUEUE_FLAG_SAME_FORCE, but actually not. blk_complete_request() is
124	 * running in interrupt handler, and currently I/O controller doesn't
125	 * support multiple interrupts, so current CPU is unique actually. This
126	 * avoids IPI sending from current CPU to the first CPU of a group.
127	 */
128	if (ccpu == cpu || shared) {
129		struct list_head *list;
130do_local:
131		list = this_cpu_ptr(&blk_cpu_done);
132		list_add_tail(&req->ipi_list, list);
133
134		/*
135		 * if the list only contains our just added request,
136		 * signal a raise of the softirq. If there are already
137		 * entries there, someone already raised the irq but it
138		 * hasn't run yet.
139		 */
140		if (list->next == &req->ipi_list)
141			raise_softirq_irqoff(BLOCK_SOFTIRQ);
142	} else if (raise_blk_irq(ccpu, req))
143		goto do_local;
144
145	local_irq_restore(flags);
146}
147
148/**
149 * blk_complete_request - end I/O on a request
150 * @req:      the request being processed
151 *
152 * Description:
153 *     Ends all I/O on a request. It does not handle partial completions,
154 *     unless the driver actually implements this in its completion callback
155 *     through requeueing. The actual completion happens out-of-order,
156 *     through a softirq handler. The user must have registered a completion
157 *     callback through blk_queue_softirq_done().
158 **/
159void blk_complete_request(struct request *req)
160{
161	if (unlikely(blk_should_fake_timeout(req->q)))
162		return;
163	if (!blk_mark_rq_complete(req))
164		__blk_complete_request(req);
165}
166EXPORT_SYMBOL(blk_complete_request);
167
168static __init int blk_softirq_init(void)
169{
170	int i;
171
172	for_each_possible_cpu(i)
173		INIT_LIST_HEAD(&per_cpu(blk_cpu_done, i));
174
175	open_softirq(BLOCK_SOFTIRQ, blk_done_softirq);
176	cpuhp_setup_state_nocalls(CPUHP_BLOCK_SOFTIRQ_DEAD,
177				  "block/softirq:dead", NULL,
178				  blk_softirq_cpu_dead);
179	return 0;
180}
181subsys_initcall(blk_softirq_init);