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Re: [BUG] spinlock lockup on CPU#0

To: Fabio Coatti <cova@xxxxxxxxxxxxxxxx>
Subject: Re: [BUG] spinlock lockup on CPU#0
From: Vegard Nossum <vegard.nossum@xxxxxxxxx>
Date: Thu, 9 Apr 2009 16:07:40 +0200
Cc: Felix Blyakher <felixb@xxxxxxx>, xfs@xxxxxxxxxxx, linux-kernel@xxxxxxxxxxxxxxx
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References: <200903301936.08477.cova@xxxxxxxxxxxxxxxx>
2009/3/30 Fabio Coatti <cova@xxxxxxxxxxxxxxxx>:
> Hi all, I've got the following BUG: report on one of our servers running
>; some background:
> we are seeing several lockups in db (mysql) servers that shows up as a sudden
> load increase and then, very quickly, the server freezes. It happens in a
> random way, sometimes after weeks, sometimes very quickly after a system
> reboot. Trying to discover the problem we installed latest (at the time of
> test) 2.6.28.X kernel and loaded it with some high disk I/O operations (find,
> dd, rsync and so on).
> We have been able  to crash a server with these tests; unfortunately we have
> been able to capture only a remote screen snapshot so I copied by hand
> (hopefully without typos) the data and this is the result is the following:


Thanks for the report.

>  [<ffffffff80213590>] ? default_idle+0x30/0x50
>  [<ffffffff8021358e>] ? default_idle+0x2e/0x50
>  [<ffffffff80213793>] ? c1e_idle+0x73/0x120
>  [<ffffffff80259f11>] ? atomic_notifier_call_chain+0x11/0x20
>  [<ffffffff8020a31f>] ? cpu_idle+0x3f/0x70
> BUG: spinlock lockup on CPU#0, find/13114, ffff8801363d2c80
> Pid: 13114, comm: find Tainted: G      D W #5
> Call Trace:
>  [<ffffffff8041a02e>] _raw_spin_lock+0x14e/0x180
>  [<ffffffff8060b691>] _spin_lock+0x51/0x70
>  [<ffffffff80231ca4>] ? task_rq_lock+0x54/0xa0
>  [<ffffffff80231ca4>] task_rq_lock+0x54/0xa0
>  [<ffffffff80234501>] try_to_wake_up+0x91/0x280
>  [<ffffffff80234720>] wake_up_process+0x10/0x20
>  [<ffffffff803bf863>] xfsbufd_wakeup+0x53/0x70
>  [<ffffffff802871e0>] shrink_slab+0x90/0x180
>  [<ffffffff80287526>] try_to_free_pages+0x256/0x3a0
>  [<ffffffff80285280>] ? isolate_pages_global+0x0/0x280
>  [<ffffffff80281166>] __alloc_pages_internal+0x1b6/0x460
>  [<ffffffff802a186d>] alloc_page_vma+0x6d/0x110
>  [<ffffffff8028d3ab>] handle_mm_fault+0x4ab/0x790
>  [<ffffffff80225293>] do_page_fault+0x463/0x870
>  [<ffffffff8060b199>] ? trace_hardirqs_off_thunk+0x3a/0x3c
>  [<ffffffff8060bf52>] error_exit+0x0/0xa9

Seems like you hit this:

 * This could deadlock.
 * But until all the XFS lowlevel code is revamped to
 * handle buffer allocation failures we can't do much.
if (!(++retries % 100))
                        "XFS: possible memory allocation "
                        "deadlock in %s (mode:0x%x)\n",
                        __func__, gfp_mask);

xfsbufd_wakeup(0, gfp_mask);
congestion_wait(WRITE, HZ/50);
goto retry;

...so my guess is that you ran out of memory (and XFS simply can't
handle it -- an error in the XFS code, of course).

My first tip, if you simply want your servers not to crash, is to
switch to another filesystem. You could at least try it and see if it
helps your problem -- that's the most straight-forward solution I can
think of.

> The machine is a dual 2216HE (2 cores) AMD with 4 Gb ram; below you can find
> the .config file. (from /proc/config.gz)
> we are seeing similar lockups (at least similar for the results) since several
> kernel revisions (starting from 2.6.25.X) and on different hardware. Several
> machines are hit by this, mostly databases (maybe for the specific usage, 
> other
> machines being apache servers, I don't know).
> Could someone give us some hints about this issue, or at least some
> suggestions on how to dig it? Of course we can do any sort of testing and
> tries.

You _could_ also try something like the attached patch. It's
completely untested, and could lead to data loss (depending on whether
the callers of this function expects/handles the error condition
gracefully). I really have no idea. If you try, be sure to back up
your data first. Good luck :-)

(It could also be something else entirely, but I think the stack trace
looks suspicious enough.)


"The animistic metaphor of the bug that maliciously sneaked in while
the programmer was not looking is intellectually dishonest as it
disguises that the error is the programmer's own creation."
        -- E. W. Dijkstra, EWD1036

Attachment: xfs-deadlock.patch
Description: Binary data

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