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Re: XFS assertion from truncate. (3.10-rc2)

To: Dave Chinner <david@xxxxxxxxxxxxx>, Linux Kernel <linux-kernel@xxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
Subject: Re: XFS assertion from truncate. (3.10-rc2)
From: Dave Jones <davej@xxxxxxxxxx>
Date: Wed, 22 May 2013 12:19:46 -0400
Delivered-to: xfs@xxxxxxxxxxx
In-reply-to: <20130522142252.GB1407@xxxxxxxxxx>
Mail-followup-to: Dave Jones <davej@xxxxxxxxxx>, Dave Chinner <david@xxxxxxxxxxxxx>, Linux Kernel <linux-kernel@xxxxxxxxxxxxxxx>, xfs@xxxxxxxxxxx
References: <20130521235410.GY29466@dastard> <20130522000803.GA19891@xxxxxxxxxx> <20130522001603.GZ29466@dastard> <20130522025605.GA29767@xxxxxxxxxx> <20130522040318.GG29466@dastard> <20130522041521.GA1837@xxxxxxxxxx> <20130522051243.GH29466@dastard> <20130522052938.GA2573@xxxxxxxxxx> <20130522055147.GI29466@dastard> <20130522142252.GB1407@xxxxxxxxxx>
User-agent: Mutt/1.5.21 (2010-09-15)
On Wed, May 22, 2013 at 10:22:52AM -0400, Dave Jones wrote:
 > On Wed, May 22, 2013 at 03:51:47PM +1000, Dave Chinner wrote:
 > 
 >  > > Tomorrow I'll also try running some older kernels with the same
 >  > > options to see if it's something new, or an older bug. This is a
 >  > > new machine, so it may be something that's been around for a
 >  > > while, and for whatever reason, my other machines don't hit
 >  > > this.
 >  > 
 >  > Another thing that just occurred to me - what compiler are you
 >  > using?  We had a report last week on #xfs that xfsdump was failing
 >  > with bad checksums because of link time optimisation (LTO) in
 >  > gcc-4.8.0. When they turned that off, everything worked fine. So if
 >  > you are using 4.8.0, perhaps trying a different compiler might be a
 >  > good idea, too.
 > 
 > Yeah, this is 4.8.0. This box is running F19-beta. 
 > I managed to shoehorn the gcc-4.7 from f18 on there though.
 > Bug reproduced instantly, so I think we can rule out compiler.
 > 
 > I ran 3.9 with the same debug options. Seems stable.
 > I'll do a bisect.

good news.  It wasn't until I started bisecting I realised I was still
carrying this patch from you to fix slab corruption I was seeing.

It seems to be the culprit (or is masking another problem -- I had to apply
it at each step of the bisect to get past the slab corruption bug).

        Dave

--- /home/davej/src/kernel/git-trees/linux/fs/xfs/xfs_extfree_item.c    
2013-05-03 10:03:05.331370231 -0400
+++ linux-dj/fs/xfs/xfs_extfree_item.c  2013-05-07 20:46:42.389262296 -0400
@@ -305,10 +305,22 @@ xfs_efi_release(xfs_efi_log_item_t        *efip
 {
        ASSERT(atomic_read(&efip->efi_next_extent) >= nextents);
        if (atomic_sub_and_test(nextents, &efip->efi_next_extent)) {
+               int recovered;
+
+               /*
+                * __xfs_efi_release() can release the last reference to the EFI
+                * and free it, so it is unsafe to reference it after we've
+                * released the reference. The only case this is safe to do is
+                * if we are in recovery and the XFS_EFI_RECOVERED bit is set,
+                * meaning that we have two references to release. Check the
+                * recovered bit before the initial release, as we cannot
+                * reliably check it afterwards.
+                */
+               recovered = test_bit(XFS_EFI_RECOVERED, &efip->efi_flags);
                __xfs_efi_release(efip);
 
                /* recovery needs us to drop the EFI reference, too */
-               if (test_bit(XFS_EFI_RECOVERED, &efip->efi_flags))
+               if (recovered)
                        __xfs_efi_release(efip);
        }
 }

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