Re: [BUG] spinlock lockup on CPU#0

Re: [BUG] spinlock lockup on CPU#0

[Vegard Nossum]

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2009/3/30 Fabio Coatti <cova@ferrara.linux.it>:
> Hi all, I've got the following BUG: report on one of our servers running
> 2.6.28.8; 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:

Hi,

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  2.6.28.8 #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))
        printk(KERN_ERR
                        "XFS: possible memory allocation "
                        "deadlock in %s (mode:0x%x)\n",
                        __func__, gfp_mask);

XFS_STATS_INC(xb_page_retries);
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.)


Vegard

-- 
"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 #2: xfs-deadlock.patch --]
[-- Type: application/octet-stream, Size: 1179 bytes --]

diff --git a/fs/xfs/linux-2.6/xfs_buf.c b/fs/xfs/linux-2.6/xfs_buf.c
index aa1016b..b79e726 100644
--- a/fs/xfs/linux-2.6/xfs_buf.c
+++ b/fs/xfs/linux-2.6/xfs_buf.c
@@ -390,29 +390,13 @@ _xfs_buf_lookup_pages(
 	      retry:
 		page = find_or_create_page(mapping, first + i, gfp_mask);
 		if (unlikely(page == NULL)) {
-			if (flags & XBF_READ_AHEAD) {
-				bp->b_page_count = i;
-				for (i = 0; i < bp->b_page_count; i++)
-					unlock_page(bp->b_pages[i]);
-				return -ENOMEM;
-			}
+			printk(KERN_EMERG "XFS couldn't find_or_create_page()\n");
+			WARN_ON_ONCE(1);
 
-			/*
-			 * 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))
-				printk(KERN_ERR
-					"XFS: possible memory allocation "
-					"deadlock in %s (mode:0x%x)\n",
-					__func__, gfp_mask);
-
-			XFS_STATS_INC(xb_page_retries);
-			xfsbufd_wakeup(0, gfp_mask);
-			congestion_wait(WRITE, HZ/50);
-			goto retry;
+			bp->b_page_count = i;
+			for (i = 0; i < bp->b_page_count; i++)
+				unlock_page(bp->b_pages[i]);
+			return -ENOMEM;
 		}
 
 		XFS_STATS_INC(xb_page_found);

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Re: [BUG] spinlock lockup on CPU#0

[Vegard Nossum]

2009/4/9 Vegard Nossum <vegard.nossum@gmail.com>:
> 2009/3/30 Fabio Coatti <cova@ferrara.linux.it>:
>> Hi all, I've got the following BUG: report on one of our servers running
>> 2.6.28.8; 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).

[...]

>> 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 :-)

Actually, I think you can forget about this patch. At least that's not
the point of problem in the stack-trace you posted. (My suggestion of
trying a different filesystem still holds, though.)

:-/


Vegard

-- 
"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

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Re: [BUG] spinlock lockup on CPU#0

[Eric Sandeen]

Vegard Nossum wrote:
> 2009/3/30 Fabio Coatti <cova@ferrara.linux.it>:
>> Hi all, I've got the following BUG: report on one of our servers running
>> 2.6.28.8; 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:
> 
> Hi,
> 
> 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  2.6.28.8 #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:

In _xfs_buf_lookup_pages?  that's not on the stack, and we didn't see
the below printk...

> /*
>  * 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))
>         printk(KERN_ERR
>                         "XFS: possible memory allocation "
>                         "deadlock in %s (mode:0x%x)\n",
>                         __func__, gfp_mask);
> 
...

so I don't think so.  From the trace:

>>  [<ffffffff803bf863>] xfsbufd_wakeup+0x53/0x70
>>  [<ffffffff802871e0>] shrink_slab+0x90/0x180

this is the shrinker kicking off:

static struct shrinker xfs_buf_shake = {
        .shrink = xfsbufd_wakeup,
        .seeks = DEFAULT_SEEKS,
};


> ...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).

Wrong guess, I think.  XFS has been called via the shrinker mechanisms
to *free* memory, and we're not able to get the task rq lock in the
wakeup path, but not sure why...

> 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.

If sysrq-t (show all running tasks) still works post-oops, capturing
that might help to see where other threads are at.  Hook up a serial
console to make capturing the output possible.

-Eric

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