From 8dc765d438f1e42b3e8227b3b09fad7d73f4ec9a Mon Sep 17 00:00:00 2001 From: Ming Lei Date: Wed, 14 Nov 2018 16:25:51 +0800 Subject: SCSI: fix queue cleanup race before queue initialization is done c2856ae2f315d ("blk-mq: quiesce queue before freeing queue") has already fixed this race, however the implied synchronize_rcu() in blk_mq_quiesce_queue() can slow down LUN probe a lot, so caused performance regression. Then 1311326cf4755c7 ("blk-mq: avoid to synchronize rcu inside blk_cleanup_queue()") tried to quiesce queue for avoiding unnecessary synchronize_rcu() only when queue initialization is done, because it is usual to see lots of inexistent LUNs which need to be probed. However, turns out it isn't safe to quiesce queue only when queue initialization is done. Because when one SCSI command is completed, the user of sending command can be waken up immediately, then the scsi device may be removed, meantime the run queue in scsi_end_request() is still in-progress, so kernel panic can be caused. In Red Hat QE lab, there are several reports about this kind of kernel panic triggered during kernel booting. This patch tries to address the issue by grabing one queue usage counter during freeing one request and the following run queue. Fixes: 1311326cf4755c7 ("blk-mq: avoid to synchronize rcu inside blk_cleanup_queue()") Cc: Andrew Jones Cc: Bart Van Assche Cc: linux-scsi@vger.kernel.org Cc: Martin K. Petersen Cc: Christoph Hellwig Cc: James E.J. Bottomley Cc: stable Cc: jianchao.wang Signed-off-by: Ming Lei Signed-off-by: Jens Axboe --- block/blk-core.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) (limited to 'block') diff --git a/block/blk-core.c b/block/blk-core.c index ce12515f9b9b..deb56932f8c4 100644 --- a/block/blk-core.c +++ b/block/blk-core.c @@ -798,9 +798,8 @@ void blk_cleanup_queue(struct request_queue *q) * dispatch may still be in-progress since we dispatch requests * 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. + * We rely on driver to deal with the race in case that queue + * initialization isn't done. */ if (q->mq_ops && blk_queue_init_done(q)) blk_mq_quiesce_queue(q); -- cgit v1.2.3