linux-kernel - Re: 3.1-rc10 oops in nameidata_to

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Date:	Thu, 24 Nov 2011 15:51:41 +0100
From:	Jan Kara <jack@...e.cz>
To:	George Spelvin <linux@...izon.com>
Cc:	linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: 3.1-rc10 oops in nameidata_to_filp

On Wed 16-11-11 06:22:46, George Spelvin wrote:
> This morning, I found the following on my laptop.  I hope the kernel
> version is recent enough to be useful; the only change between then and
> current 3.2-rc2 I noticed is an NFS lease fix, and the machine has no
> NFS exports or mounts active.
> 
> The laptop is a core 2 duo, running a 32-bit kernel with 2 GB of RAM.
> Uptime is 26 days, although obviously it's been asleep for a lot of that.
> 
> Non-ECC RAM; it *could* be just a random bit flip, but I'm sending
> this out into the world in case it's illuniating to someone with
> a deeper understanding of the relevant data structures.
> 
> It's running a copy of John Linville's wireless development tree,
> but the changes there should not affect core file system activity like
> this.  (They're mostly in drivers/net/wireless and net/wireless,
> touching *nothing* in fs/ or other core kernel code.)
> 
> The exact kernel I'm running is:
> 
> > commit 137d0943ea2cbcdbfc38606944fc0b6494f7c935
> > Merge: dfd5c52 899e3ee
> > Author: John W. Linville <linville@...driver.com>
> > Date:   Tue Oct 18 10:52:19 2011 -0400
> > 
> >     Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/torva
> 
> 899e3ee is v3.1-rc10.  The commit is available at
> http://git.kernel.org/?p=linux/kernel/git/linville/wireless-testing.git;a=commit;h=137d0943ea2cbcdbfc38606944fc0b6494f7c935
> 
> Local file sytsems are all ext3 or tmpfs.  Although I have mounted NFS
> file systems since reboot, they were all unmounted days before the oops.
  Well, probably you also have /proc and other virtual filesystems mounted
:)

> The machine is still up.  I plan on upgrading the kernel and
> rebooting unless someone would like some specific testing.
> 
> 
> BUG: unable to handle kernel NULL pointer dereference at 00000018
> IP: [<c108a788>] __dentry_open.isra.16+0x12c/0x1ed
> *pde = 00000000 
> Oops: 0000 [#1] SMP 
> Modules linked in: nfs lockd sunrpc serpent xcbc b43 mac80211 cfg80211 rfkill bcma
> 
> Pid: 15325, comm: find Not tainted 3.1.0-rc10-wl #281 Dell Inc. MXC061                          /0MG532
> EIP: 0060:[<c108a788>] EFLAGS: 00010206 CPU: 0
> EIP is at __dentry_open.isra.16+0x12c/0x1ed
> EAX: 00000000 EBX: c5c80480 ECX: 00000000 EDX: 00000000
> ESI: c003fd0c EDI: 00000000 EBP: c3c9be58 ESP: c3c9be40
>  DS: 007b ES: 007b FS: 00d8 GS: 0033 SS: 0068
> Process find (pid: 15325, ti=c3c9a000 task=f4a73390 task.ti=c3c9a000)
> Stack:
>  cef74480 f62a2d80 c3c9beec c3c9beec cef74480 c5c80480 c3c9be70 c108b309
>  00000000 c3c9beec 00000000 00000000 c3c9bea4 c10950fe 00000000 00000001
>  c003fd0c 00000024 c1093dad cef74400 00000000 00038900 c3c9beec 0000000b
> Call Trace:
>  [<c108b309>] nameidata_to_filp+0x33/0x3d
>  [<c10950fe>] do_last.isra.49+0x3dc/0x4c3
>  [<c1093dad>] ? path_init+0x20d/0x249
>  [<c10952ab>] path_openat+0xa1/0x254
>  [<c11109b7>] ? copy_to_user+0x3f/0x46
>  [<c109549e>] do_filp_open+0x26/0x67
>  [<c111080b>] ? might_fault+0x8/0xa
>  [<c109cfc3>] ? alloc_fd+0x4e/0xba
>  [<c1092ee7>] ? getname_flags+0x6d/0xad
>  [<c108b36d>] do_sys_open+0x5a/0xe5
>  [<c108b43e>] sys_openat+0x1f/0x25
>  [<c1314a90>] sysenter_do_call+0x12/0x26
> Code: 85 ff 89 43 10 75 0b 85 c0 74 14 8b 78 2c 85 ff 74 0d 89 da 89 f0 ff d7 85 c0 89 45 f0 75 4d 81 63 20 3f fc ff ff 8b 43 7c 8b 00 <8b> 50 18 8d 43 4c e8 5d 10 fe ff f6 43 21 40 0f 84 a2 00 00 00 
> EIP: [<c108a788>] __dentry_open.isra.16+0x12c/0x1ed SS:ESP 0068:c3c9be40
> CR2: 0000000000000018
> ---[ end trace 34290958b6905e19 ]---
  Interesting. So we failed at doing dereference for
file_ra_state_init(&f->f_ra, f->f_mapping->host->i_mapping);
  In particular f->f_mapping->host was NULL. That is curious since
f_mapping is normally initialized to inode->i_mapping (which has ->host
properly set) shortly before and only devices and similar special inodes
override this in their ->open() callback to something else. Furthermore I
see the process doing open() was find(1) which usually opens only
directories which do not commonly have special ->open callback. So that
makes things even more strange.

 So my guess would be that find wondered into some virtual filesystem and
that set f_mapping to something strange (or had inode->i_mapping not
initialized properly). Anyway, unless you can reproduce this and find on
which filesystem this happened, I don't know how to debug this further...

  Thanks for report!

								Honza
-- 
Jan Kara <jack@...e.cz>
SUSE Labs, CR
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