linux-kernel - Re: Possible memory allocation deadlock in kmem_alloc and hung task in xfs_log_commit_cil and xlog_cil

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Date:	Wed, 8 Jul 2015 09:37:43 +1000
From:	Dave Chinner <david@...morbit.com>
To:	Gavin Guo <gavin.guo@...onical.com>
Cc:	xfs@....sgi.com, linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: Possible memory allocation deadlock in kmem_alloc and hung task
 in xfs_log_commit_cil and xlog_cil_push

On Tue, Jul 07, 2015 at 05:29:43PM +0800, Gavin Guo wrote:
> Hi all,
> 
> Recently, we observed that there is the error message in
> Ubuntu-3.13.0-48.80:
> 
> "XFS: possible memory allocation deadlock in kmem_alloc (mode:0x8250)"
> 
> repeatedly shows in the dmesg. Temporarily, our workaround is to tune the
> parameters, such as, vfs_cache_pressure, min_free_kbytes, and dirty_ratio.
> 
> And we also found that there are different error messages regarding the
> hung tasks which happened in xfs_log_commit_cil and xlog_cil_push.
> 
> The log is available at: http://paste.ubuntu.com/11835007/
> 
> The following link seems the same problem we suffered:
> 
> XFS hangs with XFS: possible memory allocation deadlock in kmem_alloc
> http://oss.sgi.com/archives/xfs/2015-03/msg00172.html
> 
> I read the mail and found that there might be some modification regarding
> to move the memory allocation outside the ctx lock. And I also read the
> latest patch from February of 2015 to see if there is any new change
> about that. Unfortunately, I didn't find anything regarding the change (may
> be I'm not familiar with the XFS, so didn't find the commit). If it's
> possible for someone who is familiar with the code to point out the commits
> related to the bug if already exist or any status about the plan.

No commits - the approach I thought we might be able to take to
avoid the problem didn't work out. I have another idea of how we
might solve the problem, but I haven't ad a chance to prototype it
yet.

Cheers,

Dave.
-- 
Dave Chinner
david@...morbit.com
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