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blk-mq: Introduce blk_mq_quiesce_queue()

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blk_mq_quiesce_queue() waits until ongoing .queue_rq() invocations
have finished. This function does *not* wait until all outstanding
requests have finished (this means invocation of request.end_io()).
The algorithm used by blk_mq_quiesce_queue() is as follows:
* Hold either an RCU read lock or an SRCU read lock around
  .queue_rq() calls. The former is used if .queue_rq() does not
  block and the latter if .queue_rq() may block.
* blk_mq_quiesce_queue() first calls blk_mq_stop_hw_queues()
  followed by synchronize_srcu() or synchronize_rcu(). The latter
  call waits for .queue_rq() invocations that started before
  blk_mq_quiesce_queue() was called.
* The blk_mq_hctx_stopped() calls that control whether or not
  .queue_rq() will be called are called with the (S)RCU read lock
  held. This is necessary to avoid race conditions against
  blk_mq_quiesce_queue().

Signed-off-by: Bart Van Assche <bart.vanassche@sandisk.com>
Cc: Hannes Reinecke <hare@suse.com>
Cc: Johannes Thumshirn <jthumshirn@suse.de>
Reviewed-by: Sagi Grimberg <sagi@grimberg.me>
Reviewed-by: Ming Lei <tom.leiming@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@fb.com>
This commit is contained in:
Bart Van Assche 2016-11-02 10:09:51 -06:00 committed by Jens Axboe
parent 9b7dd572cc
commit 6a83e74d21
4 changed files with 69 additions and 7 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

1
block/Kconfig
View File

@ -5,6 +5,7 @@ menuconfig BLOCK
bool "Enable the block layer" if EXPERT
default y
select SBITMAP
select SRCU
help
Provide block layer support for the kernel.

71
block/blk-mq.c
View File

@ -115,6 +115,33 @@ void blk_mq_unfreeze_queue(struct request_queue *q)
}
EXPORT_SYMBOL_GPL(blk_mq_unfreeze_queue);
/**
* blk_mq_quiesce_queue() - wait until all ongoing queue_rq calls have finished
* @q: request queue.
*
* Note: this function does not prevent that the struct request end_io()
* callback function is invoked. Additionally, it is not prevented that
* new queue_rq() calls occur unless the queue has been stopped first.
*/
void blk_mq_quiesce_queue(struct request_queue *q)
{
struct blk_mq_hw_ctx *hctx;
unsigned int i;
bool rcu = false;
blk_mq_stop_hw_queues(q);
queue_for_each_hw_ctx(q, hctx, i) {
if (hctx->flags & BLK_MQ_F_BLOCKING)
synchronize_srcu(&hctx->queue_rq_srcu);
else
rcu = true;
}
if (rcu)
synchronize_rcu();
}
EXPORT_SYMBOL_GPL(blk_mq_quiesce_queue);
void blk_mq_wake_waiters(struct request_queue *q)
{
struct blk_mq_hw_ctx *hctx;
@ -766,7 +793,7 @@ static inline unsigned int queued_to_index(unsigned int queued)
* of IO. In particular, we'd like FIFO behaviour on handling existing
* items on the hctx->dispatch list. Ignore that for now.
*/
static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
static void blk_mq_process_rq_list(struct blk_mq_hw_ctx *hctx)
{
struct request_queue *q = hctx->queue;
struct request *rq;
@ -778,9 +805,6 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
if (unlikely(blk_mq_hctx_stopped(hctx)))
return;
WARN_ON(!cpumask_test_cpu(raw_smp_processor_id(), hctx->cpumask) &&
cpu_online(hctx->next_cpu));
hctx->run++;
/*
@ -871,6 +895,24 @@ static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
}
}
static void __blk_mq_run_hw_queue(struct blk_mq_hw_ctx *hctx)
{
int srcu_idx;
WARN_ON(!cpumask_test_cpu(raw_smp_processor_id(), hctx->cpumask) &&
cpu_online(hctx->next_cpu));
if (!(hctx->flags & BLK_MQ_F_BLOCKING)) {
rcu_read_lock();
blk_mq_process_rq_list(hctx);
rcu_read_unlock();
} else {
srcu_idx = srcu_read_lock(&hctx->queue_rq_srcu);
blk_mq_process_rq_list(hctx);
srcu_read_unlock(&hctx->queue_rq_srcu, srcu_idx);
}
}
/*
* It'd be great if the workqueue API had a way to pass
* in a mask and had some smarts for more clever placement.
@ -1268,7 +1310,7 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
const int is_flush_fua = bio->bi_opf & (REQ_PREFLUSH | REQ_FUA);
struct blk_mq_alloc_data data;
struct request *rq;
unsigned int request_count = 0;
unsigned int request_count = 0, srcu_idx;
struct blk_plug *plug;
struct request *same_queue_rq = NULL;
blk_qc_t cookie;
@ -1311,7 +1353,7 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
blk_mq_bio_to_request(rq, bio);
/*
* We do limited pluging. If the bio can be merged, do that.
* We do limited plugging. If the bio can be merged, do that.
* Otherwise the existing request in the plug list will be
* issued. So the plug list will have one request at most
*/
@ -1331,7 +1373,16 @@ static blk_qc_t blk_mq_make_request(struct request_queue *q, struct bio *bio)
blk_mq_put_ctx(data.ctx);
if (!old_rq)
goto done;
blk_mq_try_issue_directly(data.hctx, old_rq, &cookie);
if (!(data.hctx->flags & BLK_MQ_F_BLOCKING)) {
rcu_read_lock();
blk_mq_try_issue_directly(data.hctx, old_rq, &cookie);
rcu_read_unlock();
} else {
srcu_idx = srcu_read_lock(&data.hctx->queue_rq_srcu);
blk_mq_try_issue_directly(data.hctx, old_rq, &cookie);
srcu_read_unlock(&data.hctx->queue_rq_srcu, srcu_idx);
}
goto done;
}
@ -1610,6 +1661,9 @@ static void blk_mq_exit_hctx(struct request_queue *q,
if (set->ops->exit_hctx)
set->ops->exit_hctx(hctx, hctx_idx);
if (hctx->flags & BLK_MQ_F_BLOCKING)
cleanup_srcu_struct(&hctx->queue_rq_srcu);
blk_mq_remove_cpuhp(hctx);
blk_free_flush_queue(hctx->fq);
sbitmap_free(&hctx->ctx_map);
@ -1690,6 +1744,9 @@ static int blk_mq_init_hctx(struct request_queue *q,
flush_start_tag + hctx_idx, node))
goto free_fq;
if (hctx->flags & BLK_MQ_F_BLOCKING)
init_srcu_struct(&hctx->queue_rq_srcu);
return 0;
free_fq:

3
include/linux/blk-mq.h
View File

@ -3,6 +3,7 @@
#include <linux/blkdev.h>
#include <linux/sbitmap.h>
#include <linux/srcu.h>
struct blk_mq_tags;
struct blk_flush_queue;
@ -35,6 +36,8 @@ struct blk_mq_hw_ctx {
struct blk_mq_tags *tags;
struct srcu_struct queue_rq_srcu;
unsigned long queued;
unsigned long run;
#define BLK_MQ_MAX_DISPATCH_ORDER 7

1
include/linux/blkdev.h
View File

@ -918,6 +918,7 @@ extern void __blk_run_queue(struct request_queue *q);
extern void __blk_run_queue_uncond(struct request_queue *q);
extern void blk_run_queue(struct request_queue *);
extern void blk_run_queue_async(struct request_queue *q);
extern void blk_mq_quiesce_queue(struct request_queue *q);
extern int blk_rq_map_user(struct request_queue *, struct request *,
struct rq_map_data *, void __user *, unsigned long,
gfp_t);