Message-Id: <20070411154204.84c97c10.akpm@linux-foundation.org>
Date:	Wed, 11 Apr 2007 15:42:04 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Michal Piotrowski <michal.k.k.piotrowski@...il.com>
Cc:	xfs-masters@....sgi.com, LKML <linux-kernel@...r.kernel.org>
Subject: Re: mm snapshot broken-out-2007-04-11-02-24.tar.gz uploaded

On Thu, 12 Apr 2007 00:14:59 +0200
Michal Piotrowski <michal.k.k.piotrowski@...il.com> wrote:

> Andrew Morton napisa__(a):
> > On Wed, 11 Apr 2007 20:03:17 +0200
> > Michal Piotrowski <michal.k.k.piotrowski@...il.com> wrote:
> > 
> >> akpm@...ux-foundation.org napisa__(a):
> >>> The mm snapshot broken-out-2007-04-11-02-24.tar.gz has been uploaded to
> >>>
> >>>    ftp://ftp.kernel.org/pub/linux/kernel/people/akpm/mm/broken-out-2007-04-11-02-24.tar.gz
> >>>
> >>> It contains the following patches against 2.6.21-rc6:
> >>>
> >> After a few seconds of running test_mount_fs.sh
> >> http://www.stardust.webpages.pl/files/tbf/bitis-gabonica/broken-out-2007-04-11-02-24/test_mount_fs.sh
> >> I get this
> >>
> >> [11083.747512] Filesystem "loop4": Disabling barriers, not supported by the underlying device
> >> [11083.759050] XFS mounting filesystem loop4
> >> [11083.763769] Slab corruption: xfs_buf start=cce14938, len=272
> >> [11083.769986] Redzone: 0x5a2cf071/0x5a2cf071.
> >> [11083.774575] Last user: [<fddaacde>](xfs_buf_free+0x77/0x7b [xfs])
> >> [11083.781146] 0b0: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6c 6b 6b 6b
> >> [11083.787988] Prev obj: start=cce1481c, len=272
> >> [11083.792488] Redzone: 0x5a2cf071/0x5a2cf071.
> >> [11083.796828] Last user: [<fddaacde>](xfs_buf_free+0x77/0x7b [xfs])
> >> [11083.803131] 000: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> >> [11083.810392] 010: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> >> [11083.817677] Next obj: start=cce14a54, len=272
> >> [11083.822146] Redzone: 0x5a2cf071/0x5a2cf071.
> >> [11083.826415] Last user: [<fddaacde>](xfs_buf_free+0x77/0x7b [xfs])
> >> [11083.832784] 000: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> >> [11083.839403] 010: 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> >> [11083.852797] Ending clean XFS mount for filesystem: loop4
> >> [11083.865789] SELinux: initialized (dev loop4, type xfs), uses xattr
> >>
> > 
> > It does appear that someone (probably XFS) has done a use-after-free.
> > 
> > One way in which you perhaps catch this is to do:
> > 
> > --- a/fs/xfs/linux-2.6/xfs_buf.h~a
> > +++ a/fs/xfs/linux-2.6/xfs_buf.h
> > @@ -151,6 +151,7 @@ typedef struct xfs_buf {
> >  #ifdef XFS_BUF_LOCK_TRACKING
> >  	int			b_last_holder;
> >  #endif
> > +	char crap[1024];
> >  } xfs_buf_t;
> >  
> > 
> > and to then compile with CONFIG_DEBUG_PAGEALLOC.  The enlarged xfs_buf will
> > then get unmap-when-freed treatment and hopefully you'll get a nice oops
> > from the instruction which is corrupting that memory.  
> 
> [ 1053.655367] BUG: unable to handle kernel paging request at virtual address d6871b50
> [ 1053.663214]  printing eip:
> [ 1053.665971] fdd91dfe
> [ 1053.668207] *pde = 0005b067
> [ 1053.671088] *pte = 16871000
> [ 1053.673948] Oops: 0000 [#1]
> [ 1053.676795] PREEMPT SMP DEBUG_PAGEALLOC
> [ 1053.680793] last sysfs file: devices/platform/w83627hf.656/temp2_input
> [ 1053.687460] Modules linked in: jfs nls_base xfs reiserfs ext4dev jbd2 ext2 loop ipt_MASQUERADE iptable_nat nf_nat nfsd exportfs lockd nfs_acl autofs4 sunrpc af_packet nf_conntrack_netbios_ns ipt_REJECT nf_conntrack_ipv4 xt_state nf_conntrack nfnetlink iptable_filter ip_tables ip6t_REJECT xt_tcpudp ip6table_filter ip6_tables x_tables ipv6 binfmt_misc thermal processor fan container nvram snd_intel8x0 snd_ac97_codec ac97_bus snd_seq_dummy snd_seq_oss snd_seq_midi_event evdev snd_seq snd_seq_device snd_pcm_oss snd_mixer_oss snd_pcm snd_timer snd soundcore snd_page_alloc intel_agp i2c_i801 agpgart ide_cd cdrom rtc unix
> [ 1053.744461] CPU:    1
> [ 1053.744462] EIP:    0060:[<fdd91dfe>]    Not tainted VLI
> [ 1053.744465] EFLAGS: 00010292   (2.6.21-rc6-mm1-1 #2)
> [ 1053.757285] EIP is at xlog_iodone+0x99/0xbb [xfs]
> [ 1053.762069] eax: 00000000   ebx: d6871ae8   ecx: c04a396c   edx: 00000000
> [ 1053.769002] esi: d6871ae8   edi: d0f7def8   ebp: d0fa5f30   esp: d0fa5f18
> [ 1053.775912] ds: 007b   es: 007b   fs: 00d8  gs: 0000  ss: 0068
> [ 1053.781842] Process xfslogd/1 (pid: 3642, ti=d0fa4000 task=cac7f5a0 task.ti=d0fa4000)
> [ 1053.789660] Stack: c01339fc d0f36130 db641df8 d6871ae8 d0f3611c d6871b84 d0fa5f40 fddab492 
> [ 1053.798450]        dd2439ad d6871b88 d0fa5f70 c0133a26 c9c39db0 d0f36144 d0fa5f70 c01372d8 
> [ 1053.807213]        00000000 00000000 fddab477 d0f3611c d0f85d70 00000000 d0fa5fb0 c0134469 
> [ 1053.815902] Call Trace:
> [ 1053.818721]  [<fddab492>] xfs_buf_iodone_work+0x1b/0x3e [xfs]
> [ 1053.824830]  [<c0133a26>] run_workqueue+0x8e/0x15a
> [ 1053.829766]  [<c0134469>] worker_thread+0x108/0x116
> [ 1053.834793]  [<c013707c>] kthread+0xb5/0xe1
> [ 1053.839129]  [<c0104eb3>] kernel_thread_helper+0x7/0x10
> [ 1053.844539]  =======================
> [ 1053.848172] INFO: lockdep is turned off.
> [ 1053.852201] Code: 46 4c db fd ba 02 00 00 00 e8 61 fc 01 00 ba 02 00 00 00 eb 0f 8a 47 78 83 e0 80 3c 01 19 d2 f7 d2 83 e2 02 89 f8 e8 99 f7 ff ff <f6> 46 68 10 75 14 f0 ff 86 bc 00 00 00 7f 0b 8d 86 bc 00 00 00 
> [ 1053.872927] EIP: [<fdd91dfe>] xlog_iodone+0x99/0xbb [xfs] SS:ESP 0068:d0fa5f18
> 

Bingo.  So it seems the xfslogd_workqueue is being run after unmount has
freed the memory which it uses.  Or something along those lines.

> > 
> >> http://www.stardust.webpages.pl/files/tbf/bitis-gabonica/broken-out-2007-04-11-02-24/serialconsole.log
> >> http://www.stardust.webpages.pl/files/tbf/bitis-gabonica/broken-out-2007-04-11-02-24/mm-config
> >>
> >> BTW. I wonder when this bug will be fixed
> >> [11050.534896] =============================================
> >> [11050.541883] [ INFO: possible recursive locking detected ]
> >> [11050.547425] 2.6.21-rc6-mm1-1 #1
> >> [11050.550630] ---------------------------------------------
> >> [11050.556142] umount/3359 is trying to acquire lock:
> >> [11050.561060]  (&(&ip->i_lock)->mr_lock){----}, at: [<fdd8729a>] xfs_ilock+0x4d/0x6e [xfs]
> >> [11050.569565] 
> >> [11050.569567] but task is already holding lock:
> >> [11050.575487]  (&(&ip->i_lock)->mr_lock){----}, at: [<fdd8729a>] xfs_ilock+0x4d/0x6e [xfs]
> > 
> > An xfs thing.
> 
> Yes, I know. This is a known bug since at least 05-Jul-2006.
> 

It's probably not very important - often these things turn out to not
really be deadlockable at all.

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