linux-kernel - Re: 3.7.10+: BUG Dentry still in use [unmount of cifs cifs]

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Date:	Tue, 05 Mar 2013 11:42:46 -0800
From:	Ben Greear <greearb@...delatech.com>
To:	Jeff Layton <jlayton@...hat.com>
CC:	linux-cifs@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: 3.7.10+:  BUG Dentry still in use [unmount of cifs cifs]

On 03/05/2013 11:22 AM, Jeff Layton wrote:
> On Tue, 5 Mar 2013 14:08:49 -0500
> Jeff Layton <jlayton@...hat.com> wrote:
>
>> On Tue, 05 Mar 2013 10:54:56 -0800
>> Ben Greear <greearb@...delatech.com> wrote:
>>
>>> In doing some CIFS testing (utilizing it's feature to bind to local
>>> address..but not sure that matters), we saw this error when trying
>>> to un-mount.
>>>
>>> Our kernel is patched (nfs, some networking related patches), but there
>>> are no out-of-kernel patches to CIFS, so I don't *think* this is anything
>>> we could have caused.
>>>
>>> This problem appears to be easily reproducible, so we will be happy
>>> to test patches if anyone has any suggestions.
>>>
>>> BUG: Dentry ffff8800c07e43c0{i=45762,n=cifs2-01.7.lf-data} still in use (1) [unmount of cifs cifs]
>>> ------------[ cut here ]------------
>>> kernel BUG at /home/greearb/git/linux-3.7.dev.y/fs/dcache.c:967!
>>> invalid opcode: 0000 [#1] PREEMPT SMP
>>> Modules linked in: nls_utf8 cifs 8021q garp stp llc iptable_raw xt_CT veth nf_nat_ipv4 nf_nat fuse macvlan wanlink(O) pktgen nfsv3 nfs_acl nfsv4 auth_rpcgss nfs
>>> fscache lockd sunrpc be2iscsi iscsi_boot_sysfs bnx2i cnic uio cxgb4i cxgb4 cxgb3i cxgb3 mdio libcxgbi ib_iser rdma_cm ib_addr iw_cm ib_cm ib_sa ib_mad ib_core
>>> w83793 iscsi_tcp w83627hf libiscsi_tcp hwmon_vid libiscsi scsi_transport_iscsi coretemp mperf kvm_intel kvm i5k_amb uinput i5000_edac gpio_ich edac_core
>>> iTCO_wdt e1000e iTCO_vendor_support lpc_ich i2c_i801 pcspkr ioatdma dca microcode shpchp ipv6 floppy radeon i2c_algo_bit hwmon drm_kms_helper ttm drm i2c_core
>>> [last unloaded: iptable_nat]
>>> CPU 6
>>> Pid: 6610, comm: umount Tainted: G         C O 3.7.10+ #74 Supermicro X7DBU/X7DBU
>>> RIP: 0010:[<ffffffff811591c9>]  [<ffffffff811591c9>] shrink_dcache_for_umount_subtree+0x84/0x194
>>> RSP: 0018:ffff8800c0085dc8  EFLAGS: 00010296
>>> RAX: 0000000000000062 RBX: ffff8800c07e43c0 RCX: 0000000000000059
>>> RDX: ffffffff81bc25a8 RSI: 0000000000000046 RDI: 0000000000000246
>>> RBP: ffff8800c0085de8 R08: 0000000000000001 R09: ffff8800c0085cc8
>>> R10: 0000000000000000 R11: 0000000000000000 R12: ffff8800c050e9c0
>>> R13: ffff880128ee8000 R14: 0000000000000000 R15: ffff8800c0085f28
>>> FS:  00007f6084847840(0000) GS:ffff88012fd80000(0000) knlGS:0000000000000000
>>> CS:  0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>>> CR2: 00007f608442c3a0 CR3: 00000000c7c2d000 CR4: 00000000000007e0
>>> DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
>>> DR3: 0000000000000000 DR6: 00000000ffff0ff0 DR7: 0000000000000400
>>> Process umount (pid: 6610, threadinfo ffff8800c0084000, task ffff88012a6a0000)
>>> Stack:
>>>    ffff880128ee8310 00000000000128c0 ffff880128ee8000 ffffffffa06b96b0
>>>    ffff8800c0085e08 ffffffff81159310 ffff8800c0084000 ffff880128ee8000
>>>    ffff8800c0085e38 ffffffff81149afe ffff8800c0085e38 0000000000000021
>>> Call Trace:
>>>    [<ffffffff81159310>] shrink_dcache_for_umount+0x37/0x49
>>>    [<ffffffff81149afe>] generic_shutdown_super+0x20/0xd2
>>>    [<ffffffff81149c25>] kill_anon_super+0x11/0x1c
>>>    [<ffffffffa068b1ea>] cifs_kill_sb+0x15/0x21 [cifs]
>>>    [<ffffffff81149e48>] deactivate_locked_super+0x32/0x5e
>>>    [<ffffffff8114a942>] deactivate_super+0x40/0x46
>>>    [<ffffffff8115fdb3>] mntput_no_expire+0x12d/0x136
>>>    [<ffffffff81160b59>] sys_umount+0x321/0x34c
>>>    [<ffffffff8114f846>] ? path_put+0x1d/0x21
>>>    [<ffffffff81525229>] system_call_fastpath+0x16/0x1b
>>> Code: 50 28 4c 8b 0a 31 d2 48 85 f6 74 04 48 8b 56 40 48 05 10 03 00 00 48 89 de 48 c7 c7 9d d0 7b 81 48 89 04 24 31 c0 e8 b9 4e 3c 00 <0f> 0b eb fe 4c 8b 63 18
>>> 4c 39 e3 75 3c 48 8b 93 90 00 00 00 48
>>> RIP  [<ffffffff811591c9>] shrink_dcache_for_umount_subtree+0x84/0x194
>>>    RSP <ffff8800c0085dc8>
>>> ---[ end trace 9b2978a89532c292 ]---
>>
>> Hmmm...dentry leak. Are there any jobs queued to the cifsiod workqueue
>> when the box oopses?
>>
>
> In fact...
>
> It's just a guess, but does this patch help at all? Note that it builds
> but is otherwise untested ;). If it works we might want to go with
> something a bit less invasive but this may tell us if we're on the
> right track.

This does not fix the problem, though possibly it is still
a correct fix for some other bug.  Some more details on this test case:

We create 8 writer processes (which do one mount per thread), write some files.

Then, stop those, and un-mount.

Then, start 8 reader processes, which will create 8 mounts and then start
reading data.

Finally, stop these readers, which will stop the read IO calls and immediately
try to un-mount the the 8 mounts.  These unmount attempts cause the bug.

Thanks,
Ben


-- 
Ben Greear <greearb@...delatech.com>
Candela Technologies Inc  http://www.candelatech.com

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