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Re: XFS umount with IO errors seems to lead to memory corruption

To: Alex Lyakas <alex@xxxxxxxxxxxxxxxxx>
Subject: Re: XFS umount with IO errors seems to lead to memory corruption
From: Dave Chinner <david@xxxxxxxxxxxxx>
Date: Fri, 22 Nov 2013 09:07:13 +1100
Cc: linux-xfs@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
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On Thu, Nov 21, 2013 at 08:04:36PM +0200, Alex Lyakas wrote:
> Greetings,
> I am using stock XFS from kernel 3.8.13, compiled with kmemleak
> enabled. I am testing a particular scenario, in which the underlying
> block device returns IO errors during XFS umount. Almost in all cases
> this results in kernel crashes in various places, and sometimes
> kmemleak complains, and sometimes CPU soft lockup happens. It always
> happens after XFS messages like:

What testing are you doing?

http://xfs.org/index.php/XFS_FAQ#Q:_What_information_should_I_include_when_reporting_a_problem.3F

>  kernel: [  600.190509] XFS (dm-22): metadata I/O error: block
> 0x7600030 ("xlog_iodone") error 125 numblks 64
>  kernel: [  600.192267] XFS (dm-22): xfs_do_force_shutdown(0x2) called
> from line 1115 of file
> /mnt/compile/linux-stable/source/fs/xfs/xfs_log.c.  Return address =
> 0xffffffffa05cffa1
>  kernel: [  600.192319] XFS (dm-22): Log I/O Error Detected.  Shutting
> down filesystem
>  kernel: [  600.192392] XFS (dm-22): Unable to update superblock
> counters. Freespace may not be correct on next mount.
>  kernel: [  600.192398] XFS (dm-22): xfs_log_force: error 5 returned.
>  kernel: [  600.193687] XFS (?º.Z): Please umount the filesystem and
> rectify the problem(s)
> 
> you can see here the garbage that XFS prints instead of the block device name.
> In [1] and [2] I am attaching more kernel log from two such crashes.

So, something is corrupting memory and stamping all over the XFS
structures.

What's error 125?

#define ECANCELED       125     /* Operation Canceled */

I can't find an driver that actually returns that error to
filesystems, which....


>  kernel: [  600.227881] Modules linked in: xfs raid1 xfrm_user
> xfrm4_tunnel tunnel4 ipcomp xfrm_ipcomp esp4 ah4 scst_vdisk(O)
> iscsi_scst(O) scst(O) dm_zcache(O) dm_btrfs(O) btrfs(O) libcrc32c
> dm_iostat(O)

.... given you have a bunch of out of tree modules loaded (and some which
are experiemental) suggests that you have a problem with your
storage...

So, something is corrupting memory across a large number of
subsystems, and the trigger is some custom code to run error
injection. Can you reproduce the problem with something like
dm-faulty?

Cheers,

Dave.
-- 
Dave Chinner
david@xxxxxxxxxxxxx

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