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

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

[Dave Chinner]

From: Dave Chinner <dchinner@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@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);
 	xfs_unmountfs(mp);
 	xfs_freesb(mp);
-	xfs_inode_shrinker_unregister(mp);
 	xfs_icsb_destroy_counters(mp);
 	xfs_close_devices(mp);
 	xfs_free_fsname(mp);
-- 
1.7.1

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

[Eric Sandeen]

Dave Chinner wrote:
> From: Dave Chinner <dchinner@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@redhat.com>

Looks right to me, and is more symmetric with setup I think.

Reviewed-by: Eric Sandeen <sandeen@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);
>  	xfs_unmountfs(mp);
>  	xfs_freesb(mp);
> -	xfs_inode_shrinker_unregister(mp);
>  	xfs_icsb_destroy_counters(mp);
>  	xfs_close_devices(mp);
>  	xfs_free_fsname(mp);

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Re: [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@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@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.

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