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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