Re: [BUG REPORT] shrink_dcache_parent() loops indefinitely on a next-20240102 kernel

["Darrick J. Wong" <djwong@kernel.org>]

On Wed, Jan 03, 2024 at 12:12:12PM +0530, Chandan Babu R wrote:
> Hi,
> 
> Executing fstests' recoveryloop test group on XFS on a next-20240102 kernel
> sometimes causes the following hung task report to be printed on the console,
> 
> [  190.284008] XFS (loop5): Mounting V5 Filesystem 43ed2bb9-5b51-4bdc-af8d-af2ca7001f3f

Huh.  Which test is this, specifically?  And is this easily
reproduceable and new?  Or hard to re-trigger and who knows how long
it's been this way?

> [  190.291326] XFS (loop5): Ending clean mount
> [  190.301165] XFS (loop5): User initiated shutdown received.
> [  190.302808] XFS (loop5): Log I/O Error (0x6) detected at xfs_fs_goingdown+0x93/0xd0 [xfs] (fs/xfs/xfs_fsops.c:458).  Shutting down filesystem.
> [  190.308555] XFS (loop5): Please unmount the filesystem and rectify the problem(s)
> [  190.369214] XFS (loop5): Unmounting Filesystem 43ed2bb9-5b51-4bdc-af8d-af2ca7001f3f
> [  190.404932] XFS (loop5): Mounting V5 Filesystem 43ed2bb9-5b51-4bdc-af8d-af2ca7001f3f
> [  190.419673] XFS (loop5): Ending clean mount
> [  190.429301] XFS (loop5): User initiated shutdown received.
> [  190.431178] XFS (loop5): Log I/O Error (0x6) detected at xfs_fs_goingdown+0x93/0xd0 [xfs] (fs/xfs/xfs_fsops.c:458).  Shutting down filesystem.
> [  190.437622] XFS (loop5): Please unmount the filesystem and rectify the problem(s)
> [  369.717531] INFO: task fsstress:18269 blocked for more than 122 seconds.
> [  369.724323]       Not tainted 6.7.0-rc8-next-20240102+ #1
> [  369.727077] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
> [  369.730717] task:fsstress        state:D stack:0     pid:18269 tgid:18269 ppid:1      flags:0x00004006
> [  369.734945] Call Trace:
> [  369.736468]  <TASK>
> [  369.737768]  __schedule+0x237/0x720
> [  369.739593]  schedule+0x30/0xd0
> [  369.741310]  schedule_preempt_disabled+0x15/0x30
> [  369.743555]  rwsem_down_read_slowpath+0x240/0x4d0
> [  369.745634]  ? xlog_cil_force_seq+0x200/0x270 [xfs]
> [  369.747859]  down_read+0x49/0xa0
> [  369.749436]  super_lock+0xf1/0x120
> [  369.751008]  ? srso_alias_return_thunk+0x5/0xfbef5
> [  369.753530]  ? srso_alias_return_thunk+0x5/0xfbef5
> [  369.755865]  ? xfs_log_force+0x20c/0x230 [xfs]
> [  369.758147]  ? srso_alias_return_thunk+0x5/0xfbef5
> [  369.760391]  ? __pfx_sync_fs_one_sb+0x10/0x10
> [  369.762516]  iterate_supers+0x5a/0xe0
> [  369.764403]  ksys_sync+0x64/0xb0
> [  369.766104]  __do_sys_sync+0xe/0x20
> [  369.767856]  do_syscall_64+0x6c/0x170
> [  369.769684]  entry_SYSCALL_64_after_hwframe+0x6c/0x74
> [  369.771975] RIP: 0033:0x7f2b24e3ed5b
> [  369.773732] RSP: 002b:00007fff7183b058 EFLAGS: 00000202 ORIG_RAX: 00000000000000a2
> [  369.777022] RAX: ffffffffffffffda RBX: 000000000007a120 RCX: 00007f2b24e3ed5b
> [  369.780177] RDX: 0000000000000000 RSI: 00000000796b9c69 RDI: 0000000000000000
> [  369.783356] RBP: 028f5c28f5c28f5c R08: 0000000000000008 R09: 0000000000001010
> [  369.787096] R10: 00007f2b24e15228 R11: 0000000000000202 R12: 0000000000000000
> [  369.790256] R13: 8f5c28f5c28f5c29 R14: 00000000004034c0 R15: 00007f2b250156c0
> [  369.793499]  </TASK>
> 
> The sb->s_umount semaphore was owned by a task executing systemd-coredump. The
> systemd-coredump task was busy executing shrink_dcache_parent() as shown below,
> 
> systemd-coredum   18274 [001] 85214.162988:                probe:d_walk: (ffffffff88218580) parent_path="/" fs_type="tmpfs"
>         ffffffff88218581 d_walk+0x1 ([kernel.kallsyms])
>         ffffffff8821a8e2 shrink_dcache_parent+0x52 ([kernel.kallsyms])
>         ffffffff8821ac9b shrink_dcache_for_umount+0x3b ([kernel.kallsyms])
>         ffffffff881f9c10 generic_shutdown_super+0x20 ([kernel.kallsyms])
>         ffffffff881fa667 kill_litter_super+0x27 ([kernel.kallsyms])
>         ffffffff881fb3b5 deactivate_locked_super+0x35 ([kernel.kallsyms])
>         ffffffff88226d30 cleanup_mnt+0x100 ([kernel.kallsyms])
>         ffffffff87eef72c task_work_run+0x5c ([kernel.kallsyms])
>         ffffffff87ec9763 do_exit+0x2b3 ([kernel.kallsyms])
>         ffffffff87ec9b90 do_group_exit+0x30 ([kernel.kallsyms])
>         ffffffff87ec9c38 [unknown] ([kernel.kallsyms])
>         ffffffff88b9930c do_syscall_64+0x6c ([kernel.kallsyms])
>         ffffffff88c000e5 entry_SYSCALL_64+0xa5 ([kernel.kallsyms])

Curious.  I wonder if systemd-coredump@ is tearing down its private
/tmp or something?  I've never had systemd coredump installed on a test
vm.

> Trying to obtain more debug data via perf caused the 'perf record' task to
> indefinitely enter into the TASK_UNINTERRUPTIBLE state. I will try to recreate
> the bug and debug it further.

Doh. :(

--D
> 
> The following is the fstests configuration that was used.
>   FSTYP=xfs
>   TEST_DEV=/dev/loop7
>   TEST_DIR=/media/test
>   SCRATCH_DEV=/dev/loop5
>   SCRATCH_MNT=/media/scratch
>   MKFS_OPTIONS='-f -m reflink=1,rmapbt=1, -i sparse=1,'
>   MOUNT_OPTIONS='-o usrquota,grpquota,prjquota'
>   LOGWRITES_DEV=/dev/loop6
>   SOAK_DURATION=9900
> 
> The recoveryloop group of tests can then be executed by,
> $ ./check -g recoveryloop
> 
> -- 
> Chandan
>