linux-kernel - Re: xfs bug in 2.6.26-rc9

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Message-ID: <487B019B.9090401@sgi.com>
Date:	Mon, 14 Jul 2008 17:34:51 +1000
From:	Lachlan McIlroy <lachlan@....com>
To:	Mikael Abrahamsson <swmike@....pp.se>
CC:	Dave Chinner <david@...morbit.com>, linux-kernel@...r.kernel.org,
	xfs@....sgi.com
Subject: Re: xfs bug in 2.6.26-rc9

Mikael Abrahamsson wrote:
> On Fri, 11 Jul 2008, Dave Chinner wrote:
> 
>> That aside, what was the assert failure reported prior to the oops? 
>> i.e. paste the lines in the log before the ---[ cut here ]--- line? 
>> One of them will start with 'Assertion failed:', I think....
> 
> These ones?
> 
> Jul  8 04:44:56 via kernel: [554197.888008] Assertion failed: whichfork 
> == XFS_ATTR_FORK || ip->i_delayed_blks == 0, file: fs/xfs/xfs_bmap.c, 
> line: 5879
> Jul  9 03:25:21 via kernel: [42940.748007] Assertion failed: whichfork 
> == XFS_ATTR_FORK || ip->i_delayed_blks == 0, file: fs/xfs/xfs_bmap.c, 
> line: 5879

	xfs_ilock(ip, XFS_IOLOCK_SHARED);

	if (whichfork == XFS_DATA_FORK &&
		(ip->i_delayed_blks || ip->i_size > ip->i_d.di_size)) {
		/* xfs_fsize_t last_byte = xfs_file_last_byte(ip); */
		error = xfs_flush_pages(ip, (xfs_off_t)0,
					       -1, 0, FI_REMAPF);
		if (error) {
			xfs_iunlock(ip, XFS_IOLOCK_SHARED);
		return error;
		}
	}

	ASSERT(whichfork == XFS_ATTR_FORK || ip->i_delayed_blks == 0);

This is a race between xfs_fsr and a mmap write.  xfs_fsr acquires the
iolock and then flushes the file and because it has the iolock it doesn't
expect any new delayed allocations to occur.  A mmap write can allocate
delayed allocations without acquiring the iolock so is able to get in
after the flush but before the ASSERT.

> 
> I'll happily rebuild the kernel without the debug option and do 
> xfs_check to weed out any possible logical problem with the volume, if 
> you don't need any further information from the current state of my volume.
> 
> I should also say that this assert failue happened two nights in a row 
> so I guess it's fairly reproducible (didn't happen on the 10th, and 
> today, the 11th it seems to have panic:ed around 03:30 (I start the 
> defragmentation via cron at 03:00) which I think is related.
> 
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