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TOMOYO Linux Cross Reference
Linux/block/blk-softirq.c

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  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 
 17 static 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  */
 23 static __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
 42 static 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  */
 61 static 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 */
 77 static int raise_blk_irq(int cpu, struct request *rq)
 78 {
 79         return 1;
 80 }
 81 #endif
 82 
 83 static 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 
 98 void __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;
130 do_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  **/
159 void 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 }
166 EXPORT_SYMBOL(blk_complete_request);
167 
168 static __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 }
181 subsys_initcall(blk_softirq_init);
182 

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