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