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blk-mq: use QUEUE_FLAG_QUIESCED to quiesce queue

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It is required that no dispatch can happen any more once
blk_mq_quiesce_queue() returns, and we don't have such requirement
on APIs of stopping queue.

But blk_mq_quiesce_queue() still may not block/drain dispatch in the
the case of BLK_MQ_S_START_ON_RUN, so use the new introduced flag of
QUEUE_FLAG_QUIESCED and evaluate it inside RCU read-side critical
sections for fixing this issue.

Also blk_mq_quiesce_queue() is implemented via stopping queue, which
limits its uses, and easy to cause race, because any queue restart in
other paths may break blk_mq_quiesce_queue(). With the introduced
flag of QUEUE_FLAG_QUIESCED, we don't need to depend on stopping queue
for quiescing any more.

Signed-off-by: Ming Lei <ming.lei@redhat.com>
Reviewed-by: Bart Van Assche <Bart.VanAssche@sandisk.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
This commit is contained in:
Ming Lei 2017-06-18 14:24:27 -06:00 committed by Jens Axboe
parent f660174e8b
commit f4560ffe8c
4 changed files with 18 additions and 2 deletions
repo.diff.show_diff_stats Download patch file Download diff file Expand all files Collapse all files

3
block/blk-mq-sched.c
View file

@ -58,7 +58,8 @@ void blk_mq_sched_dispatch_requests(struct blk_mq_hw_ctx *hctx)
bool did_work = false;
LIST_HEAD(rq_list);
if (unlikely(blk_mq_hctx_stopped(hctx)))
/* RCU or SRCU read lock is needed before checking quiesced flag */
if (unlikely(blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)))
return;
hctx->run++;

11
block/blk-mq.c
View file

@ -170,6 +170,10 @@ void blk_mq_quiesce_queue(struct request_queue *q)
__blk_mq_stop_hw_queues(q, true);
spin_lock_irq(q->queue_lock);
queue_flag_set(QUEUE_FLAG_QUIESCED, q);
spin_unlock_irq(q->queue_lock);
queue_for_each_hw_ctx(q, hctx, i) {
if (hctx->flags & BLK_MQ_F_BLOCKING)
synchronize_srcu(&hctx->queue_rq_srcu);
@ -190,6 +194,10 @@ EXPORT_SYMBOL_GPL(blk_mq_quiesce_queue);
*/
void blk_mq_unquiesce_queue(struct request_queue *q)
{
spin_lock_irq(q->queue_lock);
queue_flag_clear(QUEUE_FLAG_QUIESCED, q);
spin_unlock_irq(q->queue_lock);
blk_mq_start_stopped_hw_queues(q, true);
}
EXPORT_SYMBOL_GPL(blk_mq_unquiesce_queue);
@ -1444,7 +1452,8 @@ static void __blk_mq_try_issue_directly(struct blk_mq_hw_ctx *hctx,
blk_status_t ret;
bool run_queue = true;
if (blk_mq_hctx_stopped(hctx)) {
/* RCU or SRCU read lock is needed before checking quiesced flag */
if (blk_mq_hctx_stopped(hctx) || blk_queue_quiesced(q)) {
run_queue = false;
goto insert;
}

4
include/linux/blk-mq.h
View file

@ -268,6 +268,10 @@ void blk_mq_update_nr_hw_queues(struct blk_mq_tag_set *set, int nr_hw_queues);
*/
static inline void blk_mq_quiesce_queue_nowait(struct request_queue *q)
{
spin_lock_irq(q->queue_lock);
queue_flag_set(QUEUE_FLAG_QUIESCED, q);
spin_unlock_irq(q->queue_lock);
blk_mq_stop_hw_queues(q);
}

2
include/linux/blkdev.h
View file

@ -619,6 +619,7 @@ struct request_queue {
#define QUEUE_FLAG_POLL_STATS 28 /* collecting stats for hybrid polling */
#define QUEUE_FLAG_REGISTERED 29 /* queue has been registered to a disk */
#define QUEUE_FLAG_SCSI_PASSTHROUGH 30 /* queue supports SCSI commands */
#define QUEUE_FLAG_QUIESCED 31 /* queue has been quiesced */
#define QUEUE_FLAG_DEFAULT ((1 << QUEUE_FLAG_IO_STAT) | \
(1 << QUEUE_FLAG_STACKABLE) | \
@ -715,6 +716,7 @@ static inline void queue_flag_clear(unsigned int flag, struct request_queue *q)
#define blk_noretry_request(rq) \
((rq)->cmd_flags & (REQ_FAILFAST_DEV|REQ_FAILFAST_TRANSPORT| \
REQ_FAILFAST_DRIVER))
#define blk_queue_quiesced(q) test_bit(QUEUE_FLAG_QUIESCED, &(q)->queue_flags)
static inline bool blk_account_rq(struct request *rq)
{