Re: XFS crashes with shrink_slab: xfs_reclaim_inode_shrink+0x0/0x10d negative objects to delete nr

Dave Chinner
2011-06-01T23:51:55Z

On Wed, Jun 01, 2011 at 12:54:55PM +0200, Stefan Priebe - Profihost AG wrote:
> Hi guys,
>
> we're seeing a really bad behaviour on one of our machines running
> vanilla 2.6.32.40 kernel.
>
> It freezes from time to time or processes starts to hang. At the
> same time the following message appears in the kernel log:

Perhaps 2.6.32.40 needs this patch:

commit 081003fff467ea0e727f66d5d435b4f473a789b3
Author: Johannes Weiner <hannes@cmpxchg.org>
Date: Fri Oct 1 07:43:54 2010 +0000

xfs: properly account for reclaimed inodes

When marking an inode reclaimable, a per-AG counter is increased, the
inode is tagged reclaimable in its per-AG tree, and, when this is the
first reclaimable inode in the AG, the AG entry in the per-mount tree
is also tagged.

When an inode is finally reclaimed, however, it is only deleted from
the per-AG tree. Neither the counter is decreased, nor is the parent
tree's AG entry untagged properly.

Since the tags in the per-mount tree are not cleared, the inode
shrinker iterates over all AGs that have had reclaimable inodes at one
point in time.

The counters on the other hand signal an increasing amount of slab
objects to reclaim. Since "70e60ce xfs: convert inode shrinker to
per-filesystem context" this is not a real issue anymore because the
shrinker bails out after one iteration.

But the problem was observable on a machine running v2.6.34, where the
reclaimable work increased and each process going into direct reclaim
eventually got stuck on the xfs inode shrinking path, trying to scan
several million objects.

Fix this by properly unwinding the reclaimable-state tracking of an
inode when it is reclaimed.

Signed-off-by: Johannes Weiner <hannes@cmpxchg.org>
Cc: stable@kernel.org
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Alex Elder <aelder@sgi.com>

>
> shrink_slab: xfs_reclaim_inode_shrink+0x0/0x10d negative objects to
> delete nr=-274207938304

That's an error messge that was introduced in 2.6.34, and the above
patch was introduced in 2.6.36. Obvious a bug has been backported to
2.6.32, but was the fix? It was clearly marked for stable kernels,
but I have no I have no idea if the stable kernel folks pushed it
back to .32. I really don't have the time to track what fixes were
or were not backported to what kernels because there are too many
"long term stable" kernels in existance now.

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com