Commit f4560ffe authored by Ming Lei's avatar Ming Lei Committed by Jens Axboe
Browse files

blk-mq: use QUEUE_FLAG_QUIESCED to quiesce queue 



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: default avatarMing Lei <ming.lei@redhat.com>
Reviewed-by: default avatarBart Van Assche <Bart.VanAssche@sandisk.com>
Signed-off-by: default avatarJens Axboe <axboe@kernel.dk>
parent f660174e

block/blk-mq-sched.c

+2 −1
Original line number Diff line number Diff line
@@ -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++;

block/blk-mq.c

+10 −1
Original line number Diff line number Diff line
@@ -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;

	}

include/linux/blk-mq.h

+4 −0
Original line number Diff line number Diff line
@@ -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);

}

include/linux/blkdev.h

+2 −0
Original line number Diff line number Diff line
@@ -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)

{

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