572299f03a
When IO requests are made continuously and the target block device
handles requests faster than request arrival, the request dispatch loop
keeps on repeating to dispatch the arriving requests very long time,
more than a minute. Since the loop runs as a workqueue worker task, the
very long loop duration triggers workqueue watchdog timeout and BUG [1].
To avoid the very long loop duration, break the loop periodically. When
opportunity to dispatch requests still exists, check need_resched(). If
need_resched() returns true, the dispatch loop already consumed its time
slice, then reschedule the dispatch work and break the loop. With heavy
IO load, need_resched() does not return true for 20~30 seconds. To cover
such case, check time spent in the dispatch loop with jiffies. If more
than 1 second is spent, reschedule the dispatch work and break the loop.
[1]
[ 609.691437] BUG: workqueue lockup - pool cpus=10 node=1 flags=0x0 nice=-20 stuck for 35s!
[ 609.701820] Showing busy workqueues and worker pools:
[ 609.707915] workqueue events: flags=0x0
[ 609.712615] pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/256 refcnt=2
[ 609.712626] pending: drm_fb_helper_damage_work [drm_kms_helper]
[ 609.712687] workqueue events_freezable: flags=0x4
[ 609.732943] pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/256 refcnt=2
[ 609.732952] pending: pci_pme_list_scan
[ 609.732968] workqueue events_power_efficient: flags=0x80
[ 609.751947] pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/256 refcnt=2
[ 609.751955] pending: neigh_managed_work
[ 609.752018] workqueue kblockd: flags=0x18
[ 609.769480] pwq 21: cpus=10 node=1 flags=0x0 nice=-20 active=3/256 refcnt=4
[ 609.769488] in-flight: 1020:blk_mq_run_work_fn
[ 609.769498] pending: blk_mq_timeout_work, blk_mq_run_work_fn
[ 609.769744] pool 21: cpus=10 node=1 flags=0x0 nice=-20 hung=35s workers=2 idle: 67
[ 639.899730] BUG: workqueue lockup - pool cpus=10 node=1 flags=0x0 nice=-20 stuck for 66s!
[ 639.909513] Showing busy workqueues and worker pools:
[ 639.915404] workqueue events: flags=0x0
[ 639.920197] pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/256 refcnt=2
[ 639.920215] pending: drm_fb_helper_damage_work [drm_kms_helper]
[ 639.920365] workqueue kblockd: flags=0x18
[ 639.939932] pwq 21: cpus=10 node=1 flags=0x0 nice=-20 active=3/256 refcnt=4
[ 639.939942] in-flight: 1020:blk_mq_run_work_fn
[ 639.939955] pending: blk_mq_timeout_work, blk_mq_run_work_fn
[ 639.940212] pool 21: cpus=10 node=1 flags=0x0 nice=-20 hung=66s workers=2 idle: 67
Fixes: 6e6fcbc27e778 ("blk-mq: support batching dispatch in case of io")
Signed-off-by: Shin'ichiro Kawasaki <shinichiro.kawasaki@wdc.com>
Cc: stable@vger.kernel.org # v5.10+
Link: https://lore.kernel.org/linux-block/20220310091649.zypaem5lkyfadymg@shindev/
Link: https://lore.kernel.org/r/20220318022641.133484-1-shinichiro.kawasaki@wdc.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.