dm: fix unconditional IO throttle caused by REQ_PREFLUSH

[ 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>

diff --git a/drivers/md/dm.c b/drivers/md/dm.c
index 4d1e42891d246541bfbab6f429e96b5f03c5d058..5ab7574c0c76ab939af1ed919c38da396b599c49 100644 (file)
--- a/drivers/md/dm.c
+++ b/drivers/md/dm.c
@@ -1540,14 +1540,18 @@ 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;