On 4/12/24 21:46, Mikulas Patocka wrote:
> 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 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/blk.h | 12 ------------
> drivers/md/dm-io.c | 2 +-
> include/linux/completion.h | 13 +++++++++++++
> 3 files changed, 14 insertions(+), 13 deletions(-)
>
> Index: linux-2.6/block/blk.h
> ===================================================================
> --- linux-2.6.orig/block/blk.h 2024-03-30 20:07:03.000000000 +0100
> +++ linux-2.6/block/blk.h 2024-04-12 12:45:13.000000000 +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 2024-03-30 20:07:03.000000000 +0100
> +++ linux-2.6/drivers/md/dm-io.c 2024-04-12 12:42:17.000000000 +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);
> + blk_wait_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 2023-10-31 15:31:42.000000000 +0100
> +++ linux-2.6/include/linux/completion.h 2024-04-12 12:46:08.000000000 +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 +120,16 @@ 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()" ?
> +{
> + /* 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
>
>
--
Damien Le Moal
Western Digital Research
