From: Ming Lei ming.lei@redhat.com
[ Upstream commit 1311326cf4755c7ffefd20f576144ecf46d9906b ]
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 c2856ae2f315d75(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: c2856ae2f315d75 ("blk-mq: quiesce queue before freeing queue") Reported-by: Andrew Jones drjones@redhat.com Cc: Omar Sandoval osandov@fb.com Cc: Bart Van Assche bart.vanassche@wdc.com Cc: linux-scsi@vger.kernel.org Cc: "Martin K. Petersen" martin.petersen@oracle.com Cc: Christoph Hellwig hch@lst.de Tested-by: Andrew Jones drjones@redhat.com Signed-off-by: Ming Lei ming.lei@redhat.com Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin alexander.levin@microsoft.com --- block/blk-core.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/block/blk-core.c b/block/blk-core.c index 1646ea85dade..0f5b314fc810 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -791,9 +791,13 @@ 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)) blk_mq_quiesce_queue(q);
/* for synchronous bio-based driver finish in-flight integrity i/o */