From: Jinliang Zheng alexjlzheng@gmail.com
[ Upstream commit 88f7f56d16f568f19e1a695af34a7f4a6ce537a6 ]
When a bio with REQ_PREFLUSH is submitted to dm, __send_empty_flush() generates a flush_bio with REQ_OP_WRITE | REQ_PREFLUSH | REQ_SYNC, which causes the flush_bio to be throttled by wbt_wait().
An example from v5.4, similar problem also exists in upstream:
crash> bt 2091206 PID: 2091206 TASK: ffff2050df92a300 CPU: 109 COMMAND: "kworker/u260:0" #0 [ffff800084a2f7f0] __switch_to at ffff80004008aeb8 #1 [ffff800084a2f820] __schedule at ffff800040bfa0c4 #2 [ffff800084a2f880] schedule at ffff800040bfa4b4 #3 [ffff800084a2f8a0] io_schedule at ffff800040bfa9c4 #4 [ffff800084a2f8c0] rq_qos_wait at ffff8000405925bc #5 [ffff800084a2f940] wbt_wait at ffff8000405bb3a0 #6 [ffff800084a2f9a0] __rq_qos_throttle at ffff800040592254 #7 [ffff800084a2f9c0] blk_mq_make_request at ffff80004057cf38 #8 [ffff800084a2fa60] generic_make_request at ffff800040570138 #9 [ffff800084a2fae0] submit_bio at ffff8000405703b4 #10 [ffff800084a2fb50] xlog_write_iclog at ffff800001280834 [xfs] #11 [ffff800084a2fbb0] xlog_sync at ffff800001280c3c [xfs] #12 [ffff800084a2fbf0] xlog_state_release_iclog at ffff800001280df4 [xfs] #13 [ffff800084a2fc10] xlog_write at ffff80000128203c [xfs] #14 [ffff800084a2fcd0] xlog_cil_push at ffff8000012846dc [xfs] #15 [ffff800084a2fda0] xlog_cil_push_work at ffff800001284a2c [xfs] #16 [ffff800084a2fdb0] process_one_work at ffff800040111d08 #17 [ffff800084a2fe00] worker_thread at ffff8000401121cc #18 [ffff800084a2fe70] kthread at ffff800040118de4
After commit 2def2845cc33 ("xfs: don't allow log IO to be throttled"), the metadata submitted by xlog_write_iclog() should not be throttled. But due to the existence of the dm layer, throttling flush_bio indirectly causes the metadata bio to be throttled.
Fix this by conditionally adding REQ_IDLE to flush_bio.bi_opf, which makes wbt_should_throttle() return false to avoid wbt_wait().
Signed-off-by: Jinliang Zheng alexjlzheng@tencent.com Reviewed-by: Tianxiang Peng txpeng@tencent.com Reviewed-by: Hao Peng flyingpeng@tencent.com Signed-off-by: Mikulas Patocka mpatocka@redhat.com Signed-off-by: Sasha Levin sashal@kernel.org --- drivers/md/dm.c | 8 ++++++-- 1 file changed, 6 insertions(+), 2 deletions(-)
diff --git a/drivers/md/dm.c b/drivers/md/dm.c index 19230404d8c2b..d29125ee9e72a 100644 --- a/drivers/md/dm.c +++ b/drivers/md/dm.c @@ -1541,14 +1541,18 @@ static void __send_empty_flush(struct clone_info *ci) { struct dm_table *t = ci->map; struct bio flush_bio; + blk_opf_t opf = REQ_OP_WRITE | REQ_PREFLUSH | REQ_SYNC; + + if ((ci->io->orig_bio->bi_opf & (REQ_IDLE | REQ_SYNC)) == + (REQ_IDLE | REQ_SYNC)) + opf |= REQ_IDLE;
/* * Use an on-stack bio for this, it's safe since we don't * need to reference it after submit. It's just used as * the basis for the clone(s). */ - bio_init(&flush_bio, ci->io->md->disk->part0, NULL, 0, - REQ_OP_WRITE | REQ_PREFLUSH | REQ_SYNC); + bio_init(&flush_bio, ci->io->md->disk->part0, NULL, 0, opf);
ci->bio = &flush_bio; ci->sector_count = 0;