[PATCH] xfs: unregister inode shrinker before freeing filesystem structures

[Christoph Hellwig]

On Fri, Jun 25, 2010 at 11:08:40AM +1000, Dave Chinner wrote:
> From: Dave Chinner <dchinner at redhat.com>
> 
> Currently we don't remove the XFS mount from the shrinker list until late in
> the unmount path. By this time, we have already torn down the internals of the
> filesystem (e.g. the per-ag structures), and hence if the shrinker is executed
> between the teardown and the unregistering, the shrinker will get NULL per-ag
> structure pointers and panic trying to dereference them.
> 
> Fix this by removingthe xfs mount from the shrinker list before tearing down
> it's internal structures.
> 
> Signed-off-by: Dave Chinner <dchinner at redhat.com>
> ---
>  fs/xfs/linux-2.6/xfs_super.c |    6 +++++-
>  1 files changed, 5 insertions(+), 1 deletions(-)
> 
> diff --git a/fs/xfs/linux-2.6/xfs_super.c b/fs/xfs/linux-2.6/xfs_super.c
> index e3de46c..4605cd4 100644
> --- a/fs/xfs/linux-2.6/xfs_super.c
> +++ b/fs/xfs/linux-2.6/xfs_super.c
> @@ -1156,9 +1156,13 @@ xfs_fs_put_super(
>  
>  	XFS_bflush(mp->m_ddev_targp);
>  
> +	/*
> +	 * Unregister the memory shrinker before we tear down the mount
> +	 * structure so we don't have memory reclaim racing with us here.
> +	 */
> +	xfs_inode_shrinker_unregister(mp);

Given that we register the shrinker after syncd is started for we
should also tear it down as the very first thing for symmetry resons.