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authorYufen Yu <yuyufen@huawei.com>2020-07-16 02:52:01 -0400
committerJens Axboe <axboe@kernel.dk>2020-07-17 07:14:28 -0600
commitb5718d6c00afe51ce5327cf2beae4019da0c8e74 (patch)
tree6737291920782b8fbaf65f97419c9d492a395326
parent943c4d9074aa05b86af89eec25330c1995e807c9 (diff)
block: defer flush request no matter whether we have elevator
Commit 7520872c0cf4 ("block: don't defer flushes on blk-mq + scheduling") tried to fix deadlock for cycled wait between flush requests and data request into flush_data_in_flight. The former holded all driver tags and wait for data request completion, but the latter can not complete for waiting free driver tags. After commit 923218f6166a ("blk-mq: don't allocate driver tag upfront for flush rq"), flush requests will not get driver tag before queuing into flush queue. * With elevator, flush request just get sched_tags before inserting flush queue. It will not get driver tag until issue them to driver. data request on list fq->flush_data_in_flight will complete in the end. * Without elevator, each flush request will get a driver tag when allocate request. Then data request on fq->flush_data_in_flight don't worry about lacking driver tag. In both of these cases, cycled wait cannot be true. So we may allow to defer flush request. Signed-off-by: Yufen Yu <yuyufen@huawei.com> Reviewed-by: Ming Lei <ming.lei@redhat.com> Signed-off-by: Jens Axboe <axboe@kernel.dk>
-rw-r--r--block/blk-flush.c9
1 files changed, 2 insertions, 7 deletions
diff --git a/block/blk-flush.c b/block/blk-flush.c
index 71c7f520e040..6e1543c10493 100644
--- a/block/blk-flush.c
+++ b/block/blk-flush.c
@@ -283,13 +283,8 @@ static void blk_kick_flush(struct request_queue *q, struct blk_flush_queue *fq,
if (fq->flush_pending_idx != fq->flush_running_idx || list_empty(pending))
return;
- /* C2 and C3
- *
- * For blk-mq + scheduling, we can risk having all driver tags
- * assigned to empty flushes, and we deadlock if we are expecting
- * other requests to make progress. Don't defer for that case.
- */
- if (!list_empty(&fq->flush_data_in_flight) && q->elevator &&
+ /* C2 and C3 */
+ if (!list_empty(&fq->flush_data_in_flight) &&
time_before(jiffies,
fq->flush_pending_since + FLUSH_PENDING_TIMEOUT))
return;