blk-mq: fix a hung issue when fsync

Jianchao Wang · axboe · commit 85bd6e61f34d · 2019-01-30T08:53:54.000-07:00
Florian reported a io hung issue when fsync(). It should be triggered by following race condition. data + post flush a flush blk_flush_complete_seq case REQ_FSEQ_DATA blk_flush_queue_rq issued to driver blk_mq_dispatch_rq_list try to issue a flush req failed due to NON-NCQ command .queue_rq return BLK_STS_DEV_RESOURCE request completion req->end_io // doesn't check RESTART mq_flush_data_end_io case REQ_FSEQ_POSTFLUSH blk_kick_flush do nothing because previous flush has not been completed blk_mq_run_hw_queue insert rq to hctx->dispatch due to RESTART is still set, do nothing To fix this, replace the blk_mq_run_hw_queue in mq_flush_data_end_io with blk_mq_sched_restart to check and clear the RESTART flag. Fixes: bd166ef (blk-mq-sched: add framework for MQ capable IO schedulers) Reported-by: Florian Stecker <m19@florianstecker.de> Tested-by: Florian Stecker <m19@florianstecker.de> Signed-off-by: Jianchao Wang <jianchao.w.wang@oracle.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/block/blk-flush.c b/block/blk-flush.c
@@ -335,7 +335,7 @@ static void mq_flush_data_end_io(struct request *rq, blk_status_t error)
 	blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error);
 	spin_unlock_irqrestore(&fq->mq_flush_lock, flags);
 
-	blk_mq_run_hw_queue(hctx, true);
+	blk_mq_sched_restart(hctx);
 }
 
 /**

Original file line number	Diff line number	Diff line change
`@@ -335,7 +335,7 @@ static void mq_flush_data_end_io(struct request *rq, blk_status_t error)`
`335`	`335`	`blk_flush_complete_seq(rq, fq, REQ_FSEQ_DATA, error);`
`336`	`336`	`spin_unlock_irqrestore(&fq->mq_flush_lock, flags);`
`337`	`337`
`338`		`- blk_mq_run_hw_queue(hctx, true);`
	`338`	`+ blk_mq_sched_restart(hctx);`
`339`	`339`	`}`
`340`	`340`
`341`	`341`	`/**`