[PATCH v2] dm-io: don't warn if flush takes too long time

[Mikulas Patocka <mpatocka@redhat.com>]

> > @@ -119,4 +120,16 @@ extern void complete(struct completion *
> >  extern void complete_on_current_cpu(struct completion *x);
> >  extern void complete_all(struct completion *);
> >  
> > +static inline void blk_wait_io(struct completion *done)
> 
> Since you move this function outside of the block layer, the "blk_" prefix seems
> out of place. What about renaming this to something like
> "wait_for_completion_blk_io()", or to make it clear that it is not the same as
> wait_for_completion_io(), may be "wait_for_completion_long_io()" ?

Yes. Here I'm sending a second patch that renames this function to 
wait_for_completion_long_io.

Mikulas



From: Mikulas Patocka <mpatocka@redhat.com>

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
include/linux/completion.h, 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@redhat.com>

---
 block/bio.c                |    2 +-
 block/blk-mq.c             |    2 +-
 block/blk.h                |   12 ------------
 drivers/md/dm-io.c         |    2 +-
 include/linux/completion.h |   17 +++++++++++++++++
 5 files changed, 20 insertions(+), 15 deletions(-)

Index: linux-2.6/block/blk.h
===================================================================
--- linux-2.6.orig/block/blk.h	2024-04-15 15:54:22.000000000 +0200
+++ linux-2.6/block/blk.h	2024-04-15 15:54:21.000000000 +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	2024-04-15 15:54:22.000000000 +0200
+++ linux-2.6/drivers/md/dm-io.c	2024-04-15 15:54:21.000000000 +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	2024-04-15 15:54:22.000000000 +0200
+++ linux-2.6/include/linux/completion.h	2024-04-15 15:57:14.000000000 +0200
@@ -10,6 +10,7 @@
  */
 
 #include <linux/swait.h>
+#include <linux/sched/sysctl.h>
 
 /*
  * struct completion - structure used to maintain state for a "completion"
@@ -119,4 +120,20 @@ extern void complete(struct completion *
 extern void complete_on_current_cpu(struct completion *x);
 extern void complete_all(struct completion *);
 
+/**
+ * wait_for_completion_long_io - this is like wait_for_completion_io,
+ * but it doesn't warn if the wait takes too long.
+ */
+static inline void wait_for_completion_long_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);
+}
+
 #endif
Index: linux-2.6/block/bio.c
===================================================================
--- linux-2.6.orig/block/bio.c	2024-03-30 20:07:03.000000000 +0100
+++ linux-2.6/block/bio.c	2024-04-15 15:55:13.000000000 +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	2024-03-30 20:07:03.000000000 +0100
+++ linux-2.6/block/blk-mq.c	2024-04-15 15:55:05.000000000 +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;
 }