New: WARNING: CPU: 1 PID: 6784 at fs/dcache.c:1318 umount_check+0x77/0x7b()

https://bugzilla.kernel.org/show_bug.cgi?id=88321

            Bug ID: 88321
           Summary: WARNING: CPU: 1 PID: 6784 at fs/dcache.c:1318
                    umount_check+0x77/0x7b()
           Product: File System
           Version: 2.5
    Kernel Version: 3.17.1
          Hardware: Intel
                OS: Linux
              Tree: Mainline
            Status: NEW
          Severity: high
          Priority: P1
         Component: ext4
          Assignee: [email protected]
          Reporter: [email protected]
        Regression: No

Using a modified 3.17.1 kernel. Please see BUG 86661
(https://bugzilla.kernel.org/show_bug.cgi?id=86661) for the modifications implemented. We recently encountered the following information from the kernel ring buffer:

[Fri Oct 31 19:15:13 2014] WARNING: CPU: 1 PID: 6784 at fs/dcache.c:1318
umount_check+0x77/0x7b()
[Fri Oct 31 19:15:13 2014] Modules linked in:
[Fri Oct 31 19:15:13 2014] CPU: 1 PID: 6784 Comm: umount.nfs4 Not tainted
3.17.1-gentoo20141023m-00002-gbe4fcc3 #2
[Fri Oct 31 19:15:13 2014] Hardware name: System manufacturer System Product
Name/P6X58-E PRO, BIOS 0504    07/28/2011
[Fri Oct 31 19:15:13 2014]  0000000000000526 ffff88031c70fcc8 ffffffff81800a85
0000000000000000
[Fri Oct 31 19:15:13 2014]  0000000000000000 ffff88031c70fd08 ffffffff8103c4f3
ffff88031c70fd30
[Fri Oct 31 19:15:13 2014]  ffffffff81125a28 ffff880316e7d010 0000000000015c80
ffff880326786901
[Fri Oct 31 19:15:13 2014] Call Trace:
[Fri Oct 31 19:15:13 2014]  [<ffffffff81800a85>] dump_stack+0x46/0x58
[Fri Oct 31 19:15:13 2014]  [<ffffffff8103c4f3>] warn_slowpath_common+0x7c/0x96
[Fri Oct 31 19:15:13 2014]  [<ffffffff81125a28>] ? umount_check+0x77/0x7b
[Fri Oct 31 19:15:13 2014]  [<ffffffff8103c522>] warn_slowpath_null+0x15/0x17
[Fri Oct 31 19:15:13 2014]  [<ffffffff81125a28>] umount_check+0x77/0x7b
[Fri Oct 31 19:15:13 2014]  [<ffffffff811248c6>] d_walk+0x115/0x2d4
[Fri Oct 31 19:15:13 2014]  [<ffffffff81126484>] ? do_one_tree+0x22/0x36
[Fri Oct 31 19:15:13 2014]  [<ffffffff811259b1>] ?
d_instantiate_unique+0x68/0x68
[Fri Oct 31 19:15:13 2014]  [<ffffffff81126484>] do_one_tree+0x22/0x36
[Fri Oct 31 19:15:13 2014]  [<ffffffff8112697d>]
shrink_dcache_for_umount+0x59/0x6b
[Fri Oct 31 19:15:13 2014]  [<ffffffff8111537e>]
generic_shutdown_super+0x1e/0xed
[Fri Oct 31 19:15:13 2014]  [<ffffffff811154c0>] kill_anon_super+0xe/0x19
[Fri Oct 31 19:15:13 2014]  [<ffffffff8121e439>] nfs_kill_super+0x12/0x1e
[Fri Oct 31 19:15:13 2014]  [<ffffffff81115a02>]
deactivate_locked_super+0x36/0x4b
[Fri Oct 31 19:15:13 2014]  [<ffffffff811160f1>] deactivate_super+0x3a/0x3e
[Fri Oct 31 19:15:13 2014]  [<ffffffff8112d0d4>] mntput_no_expire+0x1b0/0x1d2
[Fri Oct 31 19:15:13 2014]  [<ffffffff8112e4b3>] ? SyS_umount+0x395/0x3aa
[Fri Oct 31 19:15:13 2014]  [<ffffffff8112e4b3>] SyS_umount+0x395/0x3aa
[Fri Oct 31 19:15:13 2014]  [<ffffffff81808412>] ?
system_call_fastpath+0x16/0x1b
[Fri Oct 31 19:15:13 2014]  [<ffffffff810f072a>] ? vm_munmap+0x4e/0x5e
[Fri Oct 31 19:15:13 2014]  [<ffffffff8112cf24>] ? mnt_get_count+0x53/0x53
[Fri Oct 31 19:15:13 2014]  [<ffffffff81808412>] system_call_fastpath+0x16/0x1b
[Fri Oct 31 19:15:13 2014] ---[ end trace f8d9e04a1786ebb6 ]---

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https://bugzilla.kernel.org/show_bug.cgi?id=88321

[email protected] changed:

What |Removed |Added
----------------------------------------------------------------------------
CC| |[email protected]

--- Comment #1 from [email protected] ---
In the function nfs_kill_super for the file fs/nfs/super.c from the root of the kernel directory can you add:
nfs_put_client(server->nfs_client)
before:
generic_shutdown_super(s);
and see if that fixes your issue.

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https://bugzilla.kernel.org/show_bug.cgi?id=88321

Theodore Tso <[email protected]> changed:

What |Removed |Added
----------------------------------------------------------------------------
CC| |[email protected]

--- Comment #2 from Theodore Tso <[email protected]> ---
Please note that Nick Krause was banned from the Linux Kernel list because he has a tendency to guess, and while it was one thing to be wasting kernel developers' time, it was quite another when he was giving bad advice to users who were looking for help.

Having looked at the warning issued on line fs/dcache:1318, which is due to a dentry in the file system to be unmounted was still being used. The nfs_put_client() call has nothing to do with dentries.

If you want to try Nick's suggestion, please feel free. But it's not likely to fix things, and it might make things worse.

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[email protected] changed:

What |Removed |Added
----------------------------------------------------------------------------
CC| |[email protected]

--- Comment #3 from [email protected] ---
See if you can reproduce this on a newer kernel. Seems that this was fixed somewhere as the call to kill_anon_super no longer shows up in nfs_kill_super.

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