[PATCH v4] dm-io: don't warn if flush takes too long time

From: Mikulas Patocka
Date: Wed Apr 17 2024 - 12:52:57 EST

There was reported hang warning when using dm-integrity on the top of loop
device on XFS on a rotational disk. The warning was triggered because
flush on the loop device was too slow.

There's no easy way to reduce the latency, so I made a patch that shuts
the warning up.

There's already a function blk_wait_io that avoids the hung task warning.
This commit moves this function from block/blk.h to
kernel/sched/completion.c, renames it to wait_for_completion_long_io
(because it is not dependent on the block layer at all) and uses it in
dm-io instead of wait_for_completion_io.

[ 1352.586981] INFO: task kworker/1:2:14820 blocked for more than 120 seconds.
[ 1352.593951] Not tainted 4.18.0-552.el8_10.x86_64 #1
[ 1352.599358] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[ 1352.607202] Call Trace:
[ 1352.609670] __schedule+0x2d1/0x870
[ 1352.613173] ? update_load_avg+0x7e/0x710
[ 1352.617193] ? update_load_avg+0x7e/0x710
[ 1352.621214] schedule+0x55/0xf0
[ 1352.624371] schedule_timeout+0x281/0x320
[ 1352.628393] ? __schedule+0x2d9/0x870
[ 1352.632065] io_schedule_timeout+0x19/0x40
[ 1352.636176] wait_for_completion_io+0x96/0x100
[ 1352.640639] sync_io+0xcc/0x120 [dm_mod]
[ 1352.644592] dm_io+0x209/0x230 [dm_mod]
[ 1352.648436] ? bit_wait_timeout+0xa0/0xa0
[ 1352.652461] ? vm_next_page+0x20/0x20 [dm_mod]
[ 1352.656924] ? km_get_page+0x60/0x60 [dm_mod]
[ 1352.661298] dm_bufio_issue_flush+0xa0/0xd0 [dm_bufio]
[ 1352.666448] dm_bufio_write_dirty_buffers+0x1a0/0x1e0 [dm_bufio]
[ 1352.672462] dm_integrity_flush_buffers+0x32/0x140 [dm_integrity]
[ 1352.678567] ? lock_timer_base+0x67/0x90
[ 1352.682505] ? __timer_delete.part.36+0x5c/0x90
[ 1352.687050] integrity_commit+0x31a/0x330 [dm_integrity]
[ 1352.692368] ? __switch_to+0x10c/0x430
[ 1352.696131] process_one_work+0x1d3/0x390
[ 1352.700152] ? process_one_work+0x390/0x390
[ 1352.704348] worker_thread+0x30/0x390
[ 1352.708019] ? process_one_work+0x390/0x390
[ 1352.712214] kthread+0x134/0x150
[ 1352.715459] ? set_kthread_struct+0x50/0x50
[ 1352.719659] ret_from_fork+0x1f/0x40

Signed-off-by: Mikulas Patocka <mpatocka@xxxxxxxxxx>

---
block/bio.c | 2 +-
block/blk-mq.c | 2 +-
block/blk.h | 12 ------------
drivers/md/dm-io.c | 2 +-
include/linux/completion.h | 1 +
kernel/sched/completion.c | 20 ++++++++++++++++++++
6 files changed, 24 insertions(+), 15 deletions(-)

Index: linux-2.6/block/blk.h
===================================================================
--- linux-2.6.orig/block/blk.h 2024-04-17 18:41:50.000000000 +0200
+++ linux-2.6/block/blk.h 2024-04-17 18:41:50.000000000 +0200
@@ -72,18 +72,6 @@ static inline int bio_queue_enter(struct
return __bio_queue_enter(q, bio);
}

-static inline void blk_wait_io(struct completion *done)
-{
- /* Prevent hang_check timer from firing at us during very long I/O */
- unsigned long timeout = sysctl_hung_task_timeout_secs * HZ / 2;
-
- if (timeout)
- while (!wait_for_completion_io_timeout(done, timeout))
- ;
- else
- wait_for_completion_io(done);
-}
-
#define BIO_INLINE_VECS 4
struct bio_vec *bvec_alloc(mempool_t *pool, unsigned short *nr_vecs,
gfp_t gfp_mask);
Index: linux-2.6/drivers/md/dm-io.c
===================================================================
--- linux-2.6.orig/drivers/md/dm-io.c 2024-04-17 18:41:50.000000000 +0200
+++ linux-2.6/drivers/md/dm-io.c 2024-04-17 18:41:50.000000000 +0200
@@ -450,7 +450,7 @@ static int sync_io(struct dm_io_client *

dispatch_io(opf, num_regions, where, dp, io, 1, ioprio);

- wait_for_completion_io(&sio.wait);
+ wait_for_completion_long_io(&sio.wait);

if (error_bits)
*error_bits = sio.error_bits;
Index: linux-2.6/include/linux/completion.h
===================================================================
--- linux-2.6.orig/include/linux/completion.h 2024-04-17 18:41:50.000000000 +0200
+++ linux-2.6/include/linux/completion.h 2024-04-17 18:49:07.000000000 +0200
@@ -112,6 +112,7 @@ extern long wait_for_completion_interrup
struct completion *x, unsigned long timeout);
extern long wait_for_completion_killable_timeout(
struct completion *x, unsigned long timeout);
+extern void wait_for_completion_long_io(struct completion *x);
extern bool try_wait_for_completion(struct completion *x);
extern bool completion_done(struct completion *x);

Index: linux-2.6/block/bio.c
===================================================================
--- linux-2.6.orig/block/bio.c 2024-04-17 18:41:50.000000000 +0200
+++ linux-2.6/block/bio.c 2024-04-17 18:41:50.000000000 +0200
@@ -1378,7 +1378,7 @@ int submit_bio_wait(struct bio *bio)
bio->bi_end_io = submit_bio_wait_endio;
bio->bi_opf |= REQ_SYNC;
submit_bio(bio);
- blk_wait_io(&done);
+ wait_for_completion_long_io(&done);

return blk_status_to_errno(bio->bi_status);
}
Index: linux-2.6/block/blk-mq.c
===================================================================
--- linux-2.6.orig/block/blk-mq.c 2024-04-17 18:41:50.000000000 +0200
+++ linux-2.6/block/blk-mq.c 2024-04-17 18:41:50.000000000 +0200
@@ -1407,7 +1407,7 @@ blk_status_t blk_execute_rq(struct reque
if (blk_rq_is_poll(rq))
blk_rq_poll_completion(rq, &wait.done);
else
- blk_wait_io(&wait.done);
+ wait_for_completion_long_io(&wait.done);

return wait.ret;
}
Index: linux-2.6/kernel/sched/completion.c
===================================================================
--- linux-2.6.orig/kernel/sched/completion.c 2024-04-17 18:41:50.000000000 +0200
+++ linux-2.6/kernel/sched/completion.c 2024-04-17 18:41:50.000000000 +0200
@@ -290,6 +290,26 @@ wait_for_completion_killable_timeout(str
EXPORT_SYMBOL(wait_for_completion_killable_timeout);

/**
+ * wait_for_completion_long_io - waits for completion of a task
+ * @x: holds the state of this particular completion
+ *
+ * This is like wait_for_completion_io, but it doesn't warn if the wait takes
+ * too long.
+ */
+void wait_for_completion_long_io(struct completion *x)
+{
+ /* Prevent hang_check timer from firing at us during very long I/O */
+ unsigned long timeout = sysctl_hung_task_timeout_secs * HZ / 2;
+
+ if (timeout)
+ while (!wait_for_completion_io_timeout(x, timeout))
+ ;
+ else
+ wait_for_completion_io(x);
+}
+EXPORT_SYMBOL(wait_for_completion_long_io);
+
+/**
* try_wait_for_completion - try to decrement a completion without blocking
* @x: completion structure
*