From: David Jeffery djeffery@redhat.com
mainline inclusion from mainline-v5.18-rc1 commit 8f5fea65b06de1cc51d4fc23fb4d378d1abd6ed7 category: bugfix bugzilla: 187541, https://gitee.com/openeuler/kernel/issues/I5RUM6 CVE: NA
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When blk_mq_delay_run_hw_queues sets an hctx to run in the future, it can reset the delay length for an already pending delayed work run_work. This creates a scenario where multiple hctx may have their queues set to run, but if one runs first and finds nothing to do, it can reset the delay of another hctx and stall the other hctx's ability to run requests.
To avoid this I/O stall when an hctx's run_work is already pending, leave it untouched to run at its current designated time rather than extending its delay. The work will still run which keeps closed the race calling blk_mq_delay_run_hw_queues is needed for while also avoiding the I/O stall.
Signed-off-by: David Jeffery djeffery@redhat.com Reviewed-by: Ming Lei ming.lei@redhat.com Link: https://lore.kernel.org/r/20220131203337.GA17666@redhat Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Yu Kuai yukuai3@huawei.com Reviewed-by: Jason Yan yanaijie@huawei.com Signed-off-by: Yongqiang Liu liuyongqiang13@huawei.com --- block/blk-mq.c | 9 +++++++++ 1 file changed, 9 insertions(+)
diff --git a/block/blk-mq.c b/block/blk-mq.c index 690dbc02ab38..96debbe63ad2 100644 --- a/block/blk-mq.c +++ b/block/blk-mq.c @@ -1550,6 +1550,15 @@ void blk_mq_delay_run_hw_queues(struct request_queue *q, unsigned long msecs) if (blk_mq_hctx_stopped(hctx)) continue;
+ /* + * If there is already a run_work pending, leave the + * pending delay untouched. Otherwise, a hctx can stall + * if another hctx is re-delaying the other's work + * before the work executes. + */ + if (delayed_work_pending(&hctx->run_work)) + continue; + blk_mq_delay_run_hw_queue(hctx, msecs); } }