Re: [PATCH] Don't reset di_format in xfs_ifree()

From: Lachlan McIlroy <lachlan@sgi.com>
To: Felix Blyakher <felixb@sgi.com>
Cc: xfs-oss <xfs@oss.sgi.com>
Subject: Re: [PATCH] Don't reset di_format in xfs_ifree()
Date: Wed, 11 Feb 2009 15:15:33 +1100	[thread overview]
Message-ID: <499250E5.7030804@sgi.com> (raw)
In-Reply-To: <468EF145-F778-4420-9445-6A5505EB16D5@sgi.com>

Felix Blyakher wrote:
> 
> On Feb 10, 2009, at 6:26 PM, Lachlan McIlroy wrote:
> 
>> I hit a panic while flushing a reclaimed inode that is fairly
>> reproducible under load.
> 
> What kind of panic was that? Where in xfs_iext_get_ext() did
> it panic?

It was a bad address so I suspect that either ifp->if_u1.if_ext_irec
or ifp->if_u1.if_extents was dereferenced when they have been freed
(or not even allocated).  The correct di_format was XFS_DINODE_FMT_LOCAL
so ifp->if_u1.if_data should have been used.

> 
>> In xfs_iflush_fork() we're led to believe that there are extents
>> on this inode but there aren't any.  Actually the inode was a
>> directory.  I added some debugging to xfs_ifree() and found
>> that di_format was XFS_DINODE_FMT_LOCAL and got reset to
>> XFS_DINODE_FMT_EXTENTS and this has confused the code in
>> xfs_iflush_fork().
>>
>> [<ffffffffa0047de7>] xfs_iext_get_ext+0x6c/0xca [xfs]
> 
> I assume you're running debug xfs, as I can see xfs_iext_get_ext()
> only in assert statements.
Yes, debug.

> 
>> [<ffffffffa004a3d4>] xfs_iflush_fork+0x1b0/0x3c6 [xfs]
>> [<ffffffffa004aa3f>] xfs_iflush_int+0x455/0x5a1 [xfs]
>> [<ffffffffa004b0da>] xfs_iflush+0x229/0x2d6 [xfs]
>> [<ffffffffa007283c>] xfs_reclaim_inode+0xd8/0x10f [xfs]
>> [<ffffffffa0072976>] xfs_reclaim_inodes_ag+0x103/0x13e [xfs]
>> [<ffffffffa00729f3>] xfs_reclaim_inodes+0x42/0x60 [xfs]
>> [<ffffffffa0072d1b>] xfs_sync_worker+0x30/0x8a [xfs]
>> [<ffffffffa0073416>] xfssyncd+0x14e/0x1a2 [xfs]
>> [<ffffffffa00732c8>] ? xfssyncd+0x0/0x1a2 [xfs]
>> [<ffffffff8104fc70>] kthread+0x49/0x79
>>
>> I made this change and it passes the load test and XFSQA too.  I'm
>> not sure if this is indicative of a bigger problem though.
>>
>> Index: xfs-fix/fs/xfs/xfs_inode.c
>> ===================================================================
>> --- xfs-fix.orig/fs/xfs/xfs_inode.c
>> +++ xfs-fix/fs/xfs/xfs_inode.c
>> @@ -2165,8 +2165,6 @@ xfs_ifree(
>>      ip->i_d.di_forkoff = 0;        /* mark the attr fork not in use */
>>      ip->i_df.if_ext_max =
>>          XFS_IFORK_DSIZE(ip) / (uint)sizeof(xfs_bmbt_rec_t);
>> -    ip->i_d.di_format = XFS_DINODE_FMT_EXTENTS;
>> -    ip->i_d.di_aformat = XFS_DINODE_FMT_EXTENTS;
> 
> So, the idea here is to reset the ip->i_d. It seems strange
> to choose XFS_DINODE_FMT_EXTENTS as initializer, and even
> more strange how not changing di_aformat could affect your panic.
I figure if one (di_format) is wrong then the other probably is too.

> 
> Just asking the questions at this time.
> Felix
> 
>>      /*
>>       * Bump the generation count so no one will be confused
>>       * by reincarnations of this inode.
>>
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> 

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