Commit 1311326c authored by Ming Lei's avatar Ming Lei Committed by Jens Axboe
Browse files

blk-mq: avoid to synchronize rcu inside blk_cleanup_queue()

SCSI probing may synchronously create and destroy a lot of request_queues
for non-existent devices. Any synchronize_rcu() in queue creation or
destroy path may introduce long latency during booting, see detailed
description in comment of blk_register_queue().

This patch removes one synchronize_rcu() inside blk_cleanup_queue()
for this case, commit c2856ae2(blk-mq: quiesce queue before freeing queue)
needs synchronize_rcu() for implementing blk_mq_quiesce_queue(), but
when queue isn't initialized, it isn't necessary to do that since
only pass-through requests are involved, no original issue in
scsi_execute() at all.

Without this patch and previous one, it may take more 20+ seconds for
virtio-scsi to complete disk probe. With the two patches, the time becomes
less than 100ms.

Fixes: c2856ae2

 ("blk-mq: quiesce queue before freeing queue")
Reported-by: default avatarAndrew Jones <>
Cc: Omar Sandoval <>
Cc: Bart Van Assche <>
Cc: "Martin K. Petersen" <>
Cc: Christoph Hellwig <>
Tested-by: default avatarAndrew Jones <>
Signed-off-by: default avatarMing Lei <>
Signed-off-by: default avatarJens Axboe <>
parent 97889f9a
......@@ -762,9 +762,13 @@ void blk_cleanup_queue(struct request_queue *q)
* make sure all in-progress dispatch are completed because
* blk_freeze_queue() can only complete all requests, and
* dispatch may still be in-progress since we dispatch requests
* from more than one contexts
* from more than one contexts.
* No need to quiesce queue if it isn't initialized yet since
* blk_freeze_queue() should be enough for cases of passthrough
* request.
if (q->mq_ops)
if (q->mq_ops && blk_queue_init_done(q))
/* for synchronous bio-based driver finish in-flight integrity i/o */
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