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Re: Kernel crash in xfs_iflush_cluster (was Somebody take a look please!

To: "Dave Chinner" <david@xxxxxxxxxxxxx>
Subject: Re: Kernel crash in xfs_iflush_cluster (was Somebody take a look please!...)
From: "Janos Haar" <janos.haar@xxxxxxxxxxxx>
Date: Thu, 15 Apr 2010 09:00:49 +0200
Cc: <xiyou.wangcong@xxxxxxxxx>, <linux-kernel@xxxxxxxxxxxxxxx>, <kamezawa.hiroyu@xxxxxxxxxxxxxx>, <linux-mm@xxxxxxxxx>, <xfs@xxxxxxxxxxx>, <axboe@xxxxxxxxx>
References: <20100405224522.GZ3335@dastard> <3a5f01cad6c5$8a722c00$0400a8c0@dcccs> <20100408025822.GL11036@dastard> <11b701cad9c8$93212530$0400a8c0@dcccs> <20100412001158.GA2493@dastard> <18b101cadadf$5edbb660$0400a8c0@dcccs> <20100413083931.GW2493@dastard> <190201cadaeb$02ec22c0$0400a8c0@dcccs> <20100413113445.GZ2493@dastard> <1cd501cadb62$3a93e790$0400a8c0@dcccs> <20100414001615.GC2493@dastard>

The corruption + crash reproduced. (unfortunately)


Apr 14 01:06:33 alfa kernel: XFS mounting filesystem sdb2

This was the point of the xfs_repair more times.


----- Original Message ----- From: "Dave Chinner" <david@xxxxxxxxxxxxx>
To: "Janos Haar" <janos.haar@xxxxxxxxxxxx>
Cc: <xiyou.wangcong@xxxxxxxxx>; <linux-kernel@xxxxxxxxxxxxxxx>; <kamezawa.hiroyu@xxxxxxxxxxxxxx>; <linux-mm@xxxxxxxxx>; <xfs@xxxxxxxxxxx>; <axboe@xxxxxxxxx>
Sent: Wednesday, April 14, 2010 2:16 AM
Subject: Re: Kernel crash in xfs_iflush_cluster (was Somebody take a look please!...)

On Wed, Apr 14, 2010 at 01:36:56AM +0200, Janos Haar wrote:
----- Original Message ----- From: "Dave Chinner"
>On Tue, Apr 13, 2010 at 11:23:36AM +0200, Janos Haar wrote:
>>>If you run:
>>>$ xfs_db -r -c "inode 474253940" -c p /dev/sdb2
>>>Then I can can confirm whether there is corruption on disk or not.
>>>Probably best to sample multiple of the inode numbers from the above
>>>list of bad inodes.
>>Here is the log:
>There are multiple fields in the inode that are corrupted.
>I am really surprised that xfs-repair - even an old version - is not
>picking up the corruption....

I think i know now the reason....
My case starting to turn into more and more interesting.

(Just a little note for remember: tuesday night, i have run the old
2.8.11 xfs_repair on the partiton wich was reported as corrupt by
the kernel, but it was clean.
The system was not restarted!)

Like you suggested, today, i have tried to make a backup from the data.
During the copy, the kernel reported a lot of corrupted entries
again, and finally the kernel crashed! (with the 19 patch pack)
Unfortunately the kernel can't write the debug info into the syslog.
The system restarted automatically, the service runs again, and i
can't do another backup attempt because force of the owner.
Today night, when the traffic was in the low period, i have stopped
the service, umount the partition, and repeat the xfs_repair on the
previously reported partition on more ways.

Here you can see the results:
xfs_repair 2.8.11 run #1:

So this successfully detected and repaired the corruption.  I don't
think this is new corruption - the corrupted inode numbers are the
same as you reported a few days back.

xfs_repair 2.8.11 run #2:

echo 3 >/proc/sys/vm/drop_caches - performed

xfs_repair 2.8.11 run #3:

These two are clearing lost+found and rediscovering the
diesconnected inodes that were discovered in the first pass. Nothing
wrng here, that's just the way older repair versions behaved.

xfs_reapir 3.1.1 run #1:

And this detected nothing wrong, either.

For me, it looks like the FS gets corrupted between tuesday night
and today night.
Note: because i am expecting kernel crashes, the dirty data flush
was set for some miliseconds timeout only for prevent too much data
It was one kernel crash in this period, but the XFS have journal,
and should be cleaned correctly. (i don't think this is the problem)

The other interesting thing is, why only this partition gets
corrupted? (again, and again?)

Can you reporduce the corruption again now that the filesystem has
been repaired? I want to know (if the corruption appears again)
whether it appears in the same location as this one.

>>I mean, if i am right, the hw memory problem makes only 1-2 bit
>>corruption seriously, and the sw page handling problem makes bad
>>memory pages, no?
>RAM ECC guarantees correction of single bit errors and detection of
>double bit errors (which cause the kernel to panic, IIRC). I can't
>tell you what happens when larger errors occur, though...

Yes, but this system have non-ECC ram unfortunately.

If your hardware doesn't have ECC, then you can't rule out anything
- even a dodgy power supply can cause this sort of transient
problem. I'm not saying that this is the cause, but I've been
assuming that you're actually running hardware with ECC on RAM,
caches, buses, etc.

This makes me think this is sw problem, and not a simple memory
corruption, or the corruption can appear only for a short of time in
the hw.

If you can take the performance hit, turn on the kernel memory leak
detector and see if that catches anything.


Dave Chinner

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