Unable to unmount an XFS filesystem.

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Environment

SUSE Linux Enterprise Server 11 Service Pack 4 (SLES 11 SP4)
with Kernel < 3.0.101-108.7.1
SUSE Linux Enterprise Server 12 Service Pack 2 (SLES 12 SP2)
with Kernel < 4.4.74-92.29.1

Situation

While trying to unmount an XFS filesystem the system will hang. A stack trace of the failing umount is looking similar to this:

[<ffffffffa085358a>] xfs_wait_buftarg+0x1a/0xb0 [xfs]
[<ffffffffa08436f7>] xfs_unmountfs+0x137/0x190 [xfs]
[<ffffffffa085d0a9>] xfs_fs_put_super+0xd9/0x130 [xfs]
[<ffffffff81161d9b>] generic_shutdown_super+0x6b/0x100
[<ffffffff81161e58>] kill_block_super+0x28/0x80
[<ffffffff81162705>] deactivate_locked_super+0x35/0x90
[<ffffffff8117dc82>] release_mounts+0x72/0x90
[<ffffffff8117df3c>] put_mnt_ns+0x5c/0x80
[<ffffffff81089f22>] free_nsproxy+0x12/0x80
[<ffffffff81066c28>] exit_notify+0x18/0x190
[<ffffffff81066fce>] do_exit+0x22e/0x470
[<ffffffff8106724d>] do_group_exit+0x3d/0xb0
[<ffffffff81078287>] get_signal_to_deliver+0x247/0x480
[<ffffffff81002951>] do_signal+0x71/0x1b0
[<ffffffff81002b28>] do_notify_resume+0x98/0xb0
[<ffffffff81472d40>] int_signal+0x12/0x17
[<00000000ffffe430>] 0xffffe430
[<ffffffffffffffff>] 0xffffffffffffffff

but could be looking similar to the next stack trace as well:

 #0 [ffff88017ede3c68] schedule at ffffffff816005b1
 #1 [ffff88017ede3cc8] schedule_timeout at ffffffff81603a13
 #2 [ffff88017ede3d78] xfs_wait_buftarg at ffffffffa0aad818 [xfs]
 #3 [ffff88017ede3dd0] xfs_log_quiesce at ffffffffa0acea0b [xfs]
 #4 [ffff88017ede3de0] xfs_fs_remount at ffffffffa0ac7100 [xfs]
 #5 [ffff88017ede3e40] do_remount_sb at ffffffff81208d46
 #6 [ffff88017ede3e78] do_mount at ffffffff81225c4c
 #7 [ffff88017ede3f18] sys_mount at ffffffff812263b5
 #8 [ffff88017ede3f50] entry_SYSCALL_64_fastpath at ffffffff81604c6e
    RIP: 00007f531792b49a  RSP: 00007ffcf4093198  RFLAGS: 00000246
    RAX: ffffffffffffffda  RBX: 000055b76e833270  RCX: 00007f531792b49a
    RDX: 0000000000000000  RSI: 000055b76e835e80  RDI: 0000000000000000
    RBP: 0000000000000000   R8: 000055b76e835c90   R9: 0000000000000000
    R10: 0000000000000021  R11: 0000000000000246  R12: 0000000000000000
    R13: 00007ffcf4093238  R14: 00007ffcf4093240  R15: 00007ffcf4093320
    ORIG_RAX: 00000000000000a5  CS: 0033  SS: 002b

Resolution

This is a known problem and has been fixed with later kernel maintenance updates for SLES11 SP4 and SLES12 SP2.

Disclaimer

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