Re: kernel BUG in fs/dcache.c running nfs

Trond Myklebust
2014-09-09T16:59:35Z

On Tue, Sep 9, 2014 at 7:59 AM, Jeff Layton <jeff.layton@primarydata.com> wrote:
> On Mon, 8 Sep 2014 07:45:25 -0700
> Christoph Hellwig <hch@infradead.org> wrote:
>
>> I've reproduced a BUG in dcache.c twice now when running xfstests, once
>> without the "nfs4: queue free_lock_state job submission to nfsiod" and
>> once with that revert in.
>>
>> Both runs are using v4.1 against a Linux server with XFS on the same
>> host.
>>
>> generic/089 199s ...
>> [ 5497.402293] ------------[ cut here ]------------
>> [ 5497.403150] kernel BUG at ../fs/dcache.c:1620!
>> [ 5497.403974] invalid opcode: 0000 [#1] SMP
>> [ 5497.404826] Modules linked in:
>> [ 5497.405280] CPU: 1 PID: 14691 Comm: t_mtab Not tainted 3.17.0-rc3+ #264
>> [ 5497.405585] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2007
>> [ 5497.405585] task: ffff88007ac801d0 ti: ffff8800670a4000 task.ti: ffff8800670a4000
>> [ 5497.405585] RIP: 0010:[<ffffffff811d1345>] [<ffffffff811d1345>] d_instantiate+0x75/0x80
>> [ 5497.405585] RSP: 0018:ffff8800670a7a68 EFLAGS: 00010286
>> [ 5497.405585] RAX: 0000000000000001 RBX: ffff880066c399d8 RCX: ffff88007ac80990
>> [ 5497.405585] RDX: 0000000000000000 RSI: 0000000000000000 RDI: ffff880066c399d8
>> [ 5497.405585] RBP: ffff8800670a7a88 R08: 0000000000000001 R09: 0000000000000000
>> [ 5497.405585] R10: ffff880072f45000 R11: 000000000003fdf0 R12: ffff880066c399d8
>> [ 5497.405585] R13: ffff88007a684800 R14: ffff88007acbc280 R15: ffff8800670de000
>> [ 5497.405585] FS: 00007f6db6aae700(0000) GS:ffff88007fc80000(0000) knlGS:0000000000000000
>> [ 5497.405585] CS: 0010 DS: 0000 ES: 0000 CR0: 000000008005003b
>> [ 5497.405585] CR2: 00007f6db5f56800 CR3: 000000007ac9e000 CR4: 00000000000006e0
>> [ 5497.405585] Stack:
>> [ 5497.405585] ffff8800670a7a88 ffff880066c399d8 ffff88007a684800 ffff88007a684800
>> [ 5497.405585] ffff8800670a7b68 ffffffff8135d0c1 ffffffff00000004 ffff8800000000d0
>> [ 5497.405585] ffff88007d400180 0000000000000246 ffff8800fffffffe ffff880072f45000
>> [ 5497.405585] Call Trace:
>> [ 5497.405585] [<ffffffff8135d0c1>] nfs4_do_open.constprop.84+0x681/0x960
>> [ 5497.405585] [<ffffffff8135d459>] nfs4_atomic_open+0x9/0x20
>> [ 5497.405585] [<ffffffff8136cc3d>] nfs4_file_open+0xcd/0x1b0
>> [ 5497.405585] [<ffffffff81d9ee56>] ? _raw_spin_unlock+0x26/0x30
>> [ 5497.405585] [<ffffffff8176b73d>] ? lockref_get+0x1d/0x30
>> [ 5497.405585] [<ffffffff8136cb70>] ? nfs4_file_fsync+0xb0/0xb0
>> [ 5497.405585] [<ffffffff811b8092>] do_dentry_open.isra.13+0x1f2/0x320
>> [ 5497.405585] [<ffffffff81336f52>] ? nfs_permission+0x62/0x1d0
>> [ 5497.405585] [<ffffffff811b82ad>] finish_open+0x1d/0x30
>> [ 5497.405585] [<ffffffff811c91be>] do_last.isra.63+0x62e/0xca0
>> [ 5497.405585] [<ffffffff811c5703>] ? inode_permission+0x13/0x50
>> [ 5497.405585] [<ffffffff811c5bde>] ? link_path_walk+0x23e/0x850
>> [ 5497.405585] [<ffffffff811c98e9>] path_openat+0xb9/0x670
>> [ 5497.405585] [<ffffffff811b366b>] ? poison_obj+0x2b/0x40
>> [ 5497.405585] [<ffffffff811ca26e>] do_filp_open+0x3e/0xa0
>> [ 5497.405585] [<ffffffff811d7da1>] ? __alloc_fd+0xd1/0x120
>> [ 5497.405585] [<ffffffff811b95cc>] do_sys_open+0x13c/0x230
>> [ 5497.405585] [<ffffffff810f5bbd>] ? trace_hardirqs_on_caller+0x10d/0x1d0
>> [ 5497.405585] [<ffffffff811b96dd>] SyS_open+0x1d/0x20
>> [ 5497.405585] [<ffffffff81d9f5a9>] system_call_fastpath+0x16/0x1b
>>
>
> Odd...
>
> It looks like you hit the BUG() in d_instantiate.
>
> I don't see any calls to d_instantiate in the current nfs_code (aside
> from the one in nfs_lookup, and I don't think that's getting called
> here). d_instantiate is called by d_add though, and that gets called
> from nfs_atomic_open. Is that what happened here?
>
> Maybe you can use gdb to figure out what line of code
> "nfs4_do_open.constprop.84+0x681" actually is?
>

Hi Jeff,

I took a look at this last night. I suspect that the problem is with
error handling.

So the problem is that in the current code, we can end up attaching
the dentry to the dcache using d_add() in _nfs4_open_and_get_state. I
suspect that we're hitting an error _after_ that call, that is causing
the callers of _nfs4_do_open() to loop and retry the open (and thus
call d_add a second time).
I haven't had time to investigate where this might be happening, but
feel free to look...

Cheers
Trond

--
Trond Myklebust

Linux NFS client maintainer, PrimaryData

trond.myklebust@primarydata.com