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

To: Felix Blyakher <felixb@xxxxxxx>
Subject: Re: [PATCH] Don't reset di_format in xfs_ifree()
From: Lachlan McIlroy <lachlan@xxxxxxx>
Date: Wed, 11 Feb 2009 15:15:33 +1100
Cc: xfs-oss <xfs@xxxxxxxxxxx>
In-reply-to: <468EF145-F778-4420-9445-6A5505EB16D5@xxxxxxx>
Organization: SGI
References: <49921B3E.8040406@xxxxxxx> <468EF145-F778-4420-9445-6A5505EB16D5@xxxxxxx>
Reply-to: lachlan@xxxxxxx
User-agent: Thunderbird 2.0.0.19 (X11/20081209)
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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