The write bio is configured as follows: bio->bi_iter.bi_size = 4096, bio->bi_opf |= (REQ_SYNC | REQ_PREFLUSH | REQ_FUA), bio->bi_bdev: dm-0(dm-linear) with 1 slave device /dev/sda. submit_bio(bio), device-mapper will: Step 1. submit empty bio with (REQ_SYNC | REQ_PREFLUSH | REQ_FUA) flag to /dev/sda. Step 2. submit bio with (REQ_SYNC | REQ_FUA) flag to /dev/sda. The blk_insert_flush function will trigger sending a flush request to /dev/sda twice if the request queue does not support FUA. The second flush request is unnecessary. Signed-off-by: Yongpeng Yang <yangyongpeng1@xxxxxxxx> --- block/blk-flush.c | 3 +++ 1 file changed, 3 insertions(+) diff --git a/block/blk-flush.c b/block/blk-flush.c index a72e2a83d075..606a6a5ae089 100644 --- a/block/blk-flush.c +++ b/block/blk-flush.c @@ -445,6 +445,9 @@ bool blk_insert_flush(struct request *rq) fq->flush_data_in_flight++; spin_unlock_irq(&fq->mq_flush_lock); return false; + case REQ_FSEQ_PREFLUSH | REQ_FSEQ_POSTFLUSH: + policy &= ~REQ_FSEQ_POSTFLUSH; + fallthrough; default: /* * Mark the request as part of a flush sequence and submit it -- 2.40.1
