Merge tag 'for-linus-20170510' of git://git.infradead.org/linux-mtd
[muen/linux.git] / block / blk-softirq.c
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 #include <linux/sched/topology.h>
13
14 #include "blk.h"
15
16 static DEFINE_PER_CPU(struct list_head, blk_cpu_done);
17
18 /*
19  * Softirq action handler - move entries to local list and loop over them
20  * while passing them to the queue registered handler.
21  */
22 static __latent_entropy void blk_done_softirq(struct softirq_action *h)
23 {
24         struct list_head *cpu_list, local_list;
25
26         local_irq_disable();
27         cpu_list = this_cpu_ptr(&blk_cpu_done);
28         list_replace_init(cpu_list, &local_list);
29         local_irq_enable();
30
31         while (!list_empty(&local_list)) {
32                 struct request *rq;
33
34                 rq = list_entry(local_list.next, struct request, ipi_list);
35                 list_del_init(&rq->ipi_list);
36                 rq->q->softirq_done_fn(rq);
37         }
38 }
39
40 #ifdef CONFIG_SMP
41 static void trigger_softirq(void *data)
42 {
43         struct request *rq = data;
44         unsigned long flags;
45         struct list_head *list;
46
47         local_irq_save(flags);
48         list = this_cpu_ptr(&blk_cpu_done);
49         list_add_tail(&rq->ipi_list, list);
50
51         if (list->next == &rq->ipi_list)
52                 raise_softirq_irqoff(BLOCK_SOFTIRQ);
53
54         local_irq_restore(flags);
55 }
56
57 /*
58  * Setup and invoke a run of 'trigger_softirq' on the given cpu.
59  */
60 static int raise_blk_irq(int cpu, struct request *rq)
61 {
62         if (cpu_online(cpu)) {
63                 struct call_single_data *data = &rq->csd;
64
65                 data->func = trigger_softirq;
66                 data->info = rq;
67                 data->flags = 0;
68
69                 smp_call_function_single_async(cpu, data);
70                 return 0;
71         }
72
73         return 1;
74 }
75 #else /* CONFIG_SMP */
76 static int raise_blk_irq(int cpu, struct request *rq)
77 {
78         return 1;
79 }
80 #endif
81
82 static int blk_softirq_cpu_dead(unsigned int cpu)
83 {
84         /*
85          * If a CPU goes away, splice its entries to the current CPU
86          * and trigger a run of the softirq
87          */
88         local_irq_disable();
89         list_splice_init(&per_cpu(blk_cpu_done, cpu),
90                          this_cpu_ptr(&blk_cpu_done));
91         raise_softirq_irqoff(BLOCK_SOFTIRQ);
92         local_irq_enable();
93
94         return 0;
95 }
96
97 void __blk_complete_request(struct request *req)
98 {
99         int ccpu, cpu;
100         struct request_queue *q = req->q;
101         unsigned long flags;
102         bool shared = false;
103
104         BUG_ON(!q->softirq_done_fn);
105
106         local_irq_save(flags);
107         cpu = smp_processor_id();
108
109         /*
110          * Select completion CPU
111          */
112         if (req->cpu != -1) {
113                 ccpu = req->cpu;
114                 if (!test_bit(QUEUE_FLAG_SAME_FORCE, &q->queue_flags))
115                         shared = cpus_share_cache(cpu, ccpu);
116         } else
117                 ccpu = cpu;
118
119         /*
120          * If current CPU and requested CPU share a cache, run the softirq on
121          * the current CPU. One might concern this is just like
122          * QUEUE_FLAG_SAME_FORCE, but actually not. blk_complete_request() is
123          * running in interrupt handler, and currently I/O controller doesn't
124          * support multiple interrupts, so current CPU is unique actually. This
125          * avoids IPI sending from current CPU to the first CPU of a group.
126          */
127         if (ccpu == cpu || shared) {
128                 struct list_head *list;
129 do_local:
130                 list = this_cpu_ptr(&blk_cpu_done);
131                 list_add_tail(&req->ipi_list, list);
132
133                 /*
134                  * if the list only contains our just added request,
135                  * signal a raise of the softirq. If there are already
136                  * entries there, someone already raised the irq but it
137                  * hasn't run yet.
138                  */
139                 if (list->next == &req->ipi_list)
140                         raise_softirq_irqoff(BLOCK_SOFTIRQ);
141         } else if (raise_blk_irq(ccpu, req))
142                 goto do_local;
143
144         local_irq_restore(flags);
145 }
146
147 /**
148  * blk_complete_request - end I/O on a request
149  * @req:      the request being processed
150  *
151  * Description:
152  *     Ends all I/O on a request. It does not handle partial completions,
153  *     unless the driver actually implements this in its completion callback
154  *     through requeueing. The actual completion happens out-of-order,
155  *     through a softirq handler. The user must have registered a completion
156  *     callback through blk_queue_softirq_done().
157  **/
158 void blk_complete_request(struct request *req)
159 {
160         if (unlikely(blk_should_fake_timeout(req->q)))
161                 return;
162         if (!blk_mark_rq_complete(req))
163                 __blk_complete_request(req);
164 }
165 EXPORT_SYMBOL(blk_complete_request);
166
167 static __init int blk_softirq_init(void)
168 {
169         int i;
170
171         for_each_possible_cpu(i)
172                 INIT_LIST_HEAD(&per_cpu(blk_cpu_done, i));
173
174         open_softirq(BLOCK_SOFTIRQ, blk_done_softirq);
175         cpuhp_setup_state_nocalls(CPUHP_BLOCK_SOFTIRQ_DEAD,
176                                   "block/softirq:dead", NULL,
177                                   blk_softirq_cpu_dead);
178         return 0;
179 }
180 subsys_initcall(blk_softirq_init);