> 2023年6月27日 11:19，Eric Wheeler <bcache@xxxxxxxxxxxxxxxxxx> 写道：
>
> Hello all,
>
> We have a system running a 5.15 kernel with the following errors in dmesg
> displaying repeatedly. Ultimately the system crashed so I'll reset
> it---but I was able to get some good information out of it before it died
> so maybe we can pin it down. This happened under high CPU and disk load:
>
> [Jun26 19:24] BUG: workqueue lockup - pool cpus=0 node=0 flags=0x0 nice=0 stuck for 1382s!
> [ +0.001211] BUG: workqueue lockup - pool cpus=0 node=0 flags=0x0 nice=-20 stuck for 1381s!
> [ +0.001117] Showing busy workqueues and worker pools:
> [ +0.001081] workqueue events: flags=0x0
> [ +0.000007] pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=9/256 refcnt=10
> [ +0.000005] pending: vmstat_shepherd, kfree_rcu_monitor, drm_fb_helper_damage_work [drm_kms_helper], kfree_rcu_monitor, mlx5_timestamp_overflow [mlx5_core], mlx5_timestamp_overflow [mlx5_core], kfree_rcu_monitor, mlx5e_tx_dim_work [mlx5_core], mlx5e_rx_dim_work [mlx5_core]
> [ +0.000301] workqueue events_highpri: flags=0x10
> [ +0.000002] pwq 59: cpus=29 node=6 flags=0x0 nice=-20 active=1/256 refcnt=2
> [ +0.000004] pending: mix_interrupt_randomness
> [ +0.000006] pwq 29: cpus=14 node=7 flags=0x0 nice=-20 active=1/256 refcnt=2
> [ +0.000003] pending: mix_interrupt_randomness
> [ +0.000005] pwq 1: cpus=0 node=0 flags=0x0 nice=-20 active=1/256 refcnt=2
> [ +0.000002] pending: mix_interrupt_randomness
> [ +0.000007] workqueue events_long: flags=0x0
> [ +0.000003] pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/256 refcnt=2
> [ +0.000002] pending: br_fdb_cleanup
> [ +0.000014] workqueue events_power_efficient: flags=0x80
> [ +0.000004] pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/256 refcnt=2
> [ +0.000002] pending: fb_flashcursor
> [ +0.000008] workqueue events_freezable_power_: flags=0x84
> [ +0.000003] pwq 8: cpus=4 node=2 flags=0x0 nice=0 active=1/256 refcnt=2
> [ +0.000002] pending: disk_events_workfn
> [ +0.000019] workqueue mm_percpu_wq: flags=0x8
> [ +0.000004] pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=1/256 refcnt=3
> [ +0.000002] pending: lru_add_drain_per_cpu BAR(212)
> [ +0.000036] workqueue kblockd: flags=0x18
> [ +0.000005] pwq 9: cpus=4 node=2 flags=0x0 nice=-20 active=1/256 refcnt=2
> [ +0.000003] pending: blk_mq_timeout_work
> [ +0.000005] pwq 1: cpus=0 node=0 flags=0x0 nice=-20 active=3/256 refcnt=4
> [ +0.000003] pending: blk_mq_timeout_work, blk_mq_run_work_fn, blk_mq_run_work_fn
> [ +0.000044] workqueue bch_btree_io: flags=0x8
> [ +0.000001] pwq 62: cpus=31 node=7 flags=0x0 nice=0 active=1/256 refcnt=2
> [ +0.000004] in-flight: 3331:btree_node_write_work
> [ +0.000006] pwq 38: cpus=19 node=1 flags=0x0 nice=0 active=1/256 refcnt=2
> [ +0.000003] in-flight: 4829:btree_node_write_work
> [ +0.000005] pwq 0: cpus=0 node=0 flags=0x0 nice=0 active=7/256 refcnt=8
> [ +0.000002] pending: btree_node_write_work, btree_node_write_work, btree_node_write_work, btree_node_write_work, btree_node_write_work, btree_node_write_work, btree_node_write_work
> [ +0.000011] workqueue bcache: flags=0x8
> [ +0.000002] pwq 6: cpus=3 node=1 flags=0x0 nice=0 active=1/256 refcnt=2
> [ +0.000003] in-flight: 6295:bch_data_insert_keys
> [ +0.000073] workqueue bcache_writeback_wq: flags=0x8
> [ +0.000002] pwq 62: cpus=31 node=7 flags=0x0 nice=0 active=64/256 refcnt=65
> [ +0.000002] in-flight: 10178:write_dirty_finish, 10067:write_dirty_finish, 3302:write_dirty_finish, 10184:write_dirty_finish, 10181:write_dirty_finish, 10066:write_dirty_finish, 10105:write_dirty_finish, 10195:write_dirty_finish, 980:write_dirty_finish, 10141:write_dirty_finish, 10139:write_dirty_finish, 10098:write_dirty_finish, 10008:write_dirty_finish, 10180:write_dirty_finish, 20178:write_dirty_finish, 3252:write_dirty_finish, 10007:write_dirty_finish, 10279:write_dirty_finish, 10142:write_dirty_finish, 10223:write_dirty_finish, 10097:write_dirty_finish, 7311:write_dirty_finish, 10234:write_dirty_finish, 10196:write_dirty_finish, 10280:write_dirty_finish, 10063:write_dirty_finish, 10064:write_dirty_finish, 10188:write_dirty_finish, 10043:write_dirty_finish, 10101:write_dirty_finish, 10185:write_dirty_finish, 10103:write_dirty_finish, 10102:write_dirty_finish, 10224:write_dirty_finish, 10186:write_dirty_finish, 10114:write_dirty_finish, 10011:write_dirty_finish
> [ +0.000083] , 3253:write_dirty_finish, 10112:write_dirty_finish, 10187:write_dirty_finish, 10009:write_dirty_finish, 10138:write_dirty_finish, 10104:write_dirty_finish, 10140:write_dirty_finish, 10065:write_dirty_finish, 10193:write_dirty_finish, 10095:write_dirty_finish, 10041:write_dirty_finish, 10010:write_dirty_finish, 10115:write_dirty_finish, 10094:write_dirty_finish, 10113:write_dirty_finish, 10194:write_dirty_finish, 10177:write_dirty_finish, 10042:write_dirty_finish, 10226:write_dirty_finish, 10179:write_dirty_finish, 10096:write_dirty_finish, 10192:write_dirty_finish, 10222:write_dirty_finish, 10045:write_dirty_finish, 10116:write_dirty_finish, 10044:write_dirty_finish, 10225:write_dirty_finish
> [ +0.000133] workqueue kcopyd: flags=0x8
> [ +0.000004] pwq 2: cpus=1 node=0 flags=0x0 nice=0 active=2/256 refcnt=3
> [ +0.000003] in-flight: 3424:do_work [dm_mod] do_work [dm_mod]
> [ +0.000520] pool 2: cpus=1 node=0 flags=0x0 nice=0 hung=14s workers=3 idle: 21748 21749
> [ +0.000006] pool 6: cpus=3 node=1 flags=0x0 nice=0 hung=43s workers=3 idle: 11428 25181
> [ +0.000006] pool 38: cpus=19 node=1 flags=0x0 nice=0 hung=34s workers=3 idle: 22403 25014
> [ +0.000006] pool 62: cpus=31 node=7 flags=0x0 nice=0 hung=2s workers=68 idle: 10281 23228 10286
>
> Clearly there are many write_dirty_finish() calls stuck, here are some
> traces:
>
> I did `cat /proc/<pid>/stack` for each bcache workqueue PID and these
> are the unique stacks:
>
> dmesg | grep in-flight | \
> perl -lne 'while(/(\d+):((write_dirty|bch|btree)\S+)/g) { print "$1 $2" }' | \
> sort -u | \
> while read a b; do echo === $a $b ; cat /proc/$a/stack; done
>
> Which prints lots of these:
>
> === 3253: write_dirty_finish
> [<0>] rwsem_down_write_slowpath+0x27b/0x4bd
> [<0>] bch_btree_node_get.part.0+0x7e/0x2d7 <<<, _probably_ called with write=true
> [<0>] bch_btree_map_nodes_recurse+0xed/0x1a7 | since this is an insert
> [<0>] __bch_btree_map_nodes+0x17c/0x1c4
> [<0>] bch_btree_insert+0x102/0x188 <<<<< race?
> [<0>] write_dirty_finish+0x122/0x1d3 <<<<< entry
> [<0>] process_one_work+0x1f1/0x3c6
> [<0>] worker_thread+0x53/0x3e4
> [<0>] kthread+0x127/0x144
> [<0>] ret_from_fork+0x22/0x2d
>
> and one of these:
> === 6295 bch_data_insert_keys
> [<0>] bch_btree_insert_node+0x6b/0x287
> [<0>] btree_insert_fn+0x20/0x48
> [<0>] bch_btree_map_nodes_recurse+0x111/0x1a7
> [<0>] __bch_btree_map_nodes+0x17c/0x1c4
> [<0>] bch_btree_insert+0x102/0x188 <<<<< race?
> [<0>] bch_data_insert_keys+0x30/0xba <<<<< entry
> [<0>] process_one_work+0x1f1/0x3c6
> [<0>] worker_thread+0x53/0x3e4
> [<0>] kthread+0x127/0x144
> [<0>] ret_from_fork+0x22/0x2d
>
> Note that above, both threads (workqueues) are similar until they call
> bch_btree_map_nodes_recurse(), then they diverge where one is doing
> bch_btree_insert_node(), which holds b->write_lock:
>
> bch_btree_insert_node
> https://elixir.bootlin.com/linux/latest/source/drivers/md/bcache/btree.c#L2322
>
> and the other is trying bch_btree_node_get(). While I don't have debug
> data about the arguments, I am guessing that bch_btree_node_get is
> called with `write=true` since the caller is bch_btree_insert:
>
> /* bch_btree_node_get - find a btree node in the cache and lock it, reading it
> * in from disk if necessary. */
> https://elixir.bootlin.com/linux/v6.4/source/drivers/md/bcache/btree.c#L969
>
> The call to bch_btree_node_get() does quite a bit of rw_lock/rw_unlock/mutex work.
>
> There are also two of the traces below which are waiting on a down():
> https://elixir.bootlin.com/linux/latest/source/drivers/md/bcache/btree.c#L420
>
> These could be relevant since __bch_btree_node_write() does call
> `lockdep_assert_held(&b->write_lock)` and b->write_lock is held above by
> bch_btree_insert_node:
>
> === 3331 btree_node_write_work
> [<0>] down+0x43/0x54
> [<0>] __bch_btree_node_write+0xa3/0x220
> [<0>] btree_node_write_work+0x43/0x4f
> [<0>] process_one_work+0x1f1/0x3c6
> [<0>] worker_thread+0x53/0x3e4
> [<0>] kthread+0x127/0x144
> [<0>] ret_from_fork+0x22/0x2d
>
> === 4829 btree_node_write_work
> [<0>] down+0x43/0x54
> [<0>] __bch_btree_node_write+0xa3/0x220
> [<0>] btree_node_write_work+0x43/0x4f
> [<0>] process_one_work+0x1f1/0x3c6
> [<0>] worker_thread+0x53/0x3e4
> [<0>] kthread+0x127/0x144
> [<0>] ret_from_fork+0x22/0x2d
>
> Thanks for your help!
When does this lockup happen? Is it in initialization or bootup time ?
Thank.
Coly Li
