[Cluster-devel] GFS2: Fix panic in glock memory shrinker

[Cluster-devel] GFS2: Fix panic in glock memory shrinker

[Benjamin Marzinski]

To: cluster-devel@redhat.com
Subject: GFS2: Fix panic in glock memory shrinker

It is possible for gfs2_shrink_glock_memory() to check a glock for
demotion
that's in the process of being freed by gfs2_glock_put().  In this case,
gfs2_shrink_glock_memory() will acquire a new reference to this glock,
and
then try to free the glock itself when it drops the refernce.  To solve
this, gfs2_shrink_glock_memory() just needs to check if the glock is in
the process of being freed, and if so skip it without ever unlocking the
lru_lock.

Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
---
 fs/gfs2/glock.c |    4 ++++
 1 file changed, 4 insertions(+)

Index: kernel-upstream/fs/gfs2/glock.c
===================================================================
--- kernel-upstream.orig/fs/gfs2/glock.c
+++ kernel-upstream/fs/gfs2/glock.c
@@ -1314,6 +1314,10 @@ static int gfs2_shrink_glock_memory(int 
 		list_del_init(&gl->gl_lru);
 		atomic_dec(&lru_count);
 
+		/* Check if glock is about to be freed */
+		if (atomic_read(&gl->gl_ref) == 0)
+			continue;
+
 		/* Test for being demotable */
 		if (!test_and_set_bit(GLF_LOCK, &gl->gl_flags)) {
 			gfs2_glock_hold(gl);

[Cluster-devel] GFS2: Fix panic in glock memory shrinker

[Bob Peterson]

----- "Benjamin Marzinski" <bmarzins@redhat.com> wrote:
| To: cluster-devel at redhat.com
| Subject: GFS2: Fix panic in glock memory shrinker
| 
| It is possible for gfs2_shrink_glock_memory() to check a glock for
| demotion
| that's in the process of being freed by gfs2_glock_put().  In this
| case,
| gfs2_shrink_glock_memory() will acquire a new reference to this
| glock,
| and
| then try to free the glock itself when it drops the refernce.  To
| solve
| this, gfs2_shrink_glock_memory() just needs to check if the glock is
| in
| the process of being freed, and if so skip it without ever unlocking
| the
| lru_lock.
| 
| Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
| ---
|  fs/gfs2/glock.c |    4 ++++
|  1 file changed, 4 insertions(+)
| 
| Index: kernel-upstream/fs/gfs2/glock.c
| ===================================================================
| --- kernel-upstream.orig/fs/gfs2/glock.c
| +++ kernel-upstream/fs/gfs2/glock.c
| @@ -1314,6 +1314,10 @@ static int gfs2_shrink_glock_memory(int 
|  		list_del_init(&gl->gl_lru);
|  		atomic_dec(&lru_count);
|  
| +		/* Check if glock is about to be freed */
| +		if (atomic_read(&gl->gl_ref) == 0)
| +			continue;
| +
|  		/* Test for being demotable */
|  		if (!test_and_set_bit(GLF_LOCK, &gl->gl_flags)) {
|  			gfs2_glock_hold(gl);

Hi,

ACKed by Bob Peterson <rpeterso@redhat.com>

Regards,

Bob Peterson
Red Hat File Systems

[Cluster-devel] GFS2: Fix panic in glock memory shrinker

[Steven Whitehouse]

Hi,

Now in the -nmw git tree. Thanks,

Steve.

On Tue, 2009-06-30 at 13:51 -0500, Benjamin Marzinski wrote:
> To: cluster-devel at redhat.com
> Subject: GFS2: Fix panic in glock memory shrinker
> 
> It is possible for gfs2_shrink_glock_memory() to check a glock for
> demotion
> that's in the process of being freed by gfs2_glock_put().  In this case,
> gfs2_shrink_glock_memory() will acquire a new reference to this glock,
> and
> then try to free the glock itself when it drops the refernce.  To solve
> this, gfs2_shrink_glock_memory() just needs to check if the glock is in
> the process of being freed, and if so skip it without ever unlocking the
> lru_lock.
> 
> Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
> ---
>  fs/gfs2/glock.c |    4 ++++
>  1 file changed, 4 insertions(+)
> 
> Index: kernel-upstream/fs/gfs2/glock.c
> ===================================================================
> --- kernel-upstream.orig/fs/gfs2/glock.c
> +++ kernel-upstream/fs/gfs2/glock.c
> @@ -1314,6 +1314,10 @@ static int gfs2_shrink_glock_memory(int 
>  		list_del_init(&gl->gl_lru);
>  		atomic_dec(&lru_count);
>  
> +		/* Check if glock is about to be freed */
> +		if (atomic_read(&gl->gl_ref) == 0)
> +			continue;
> +
>  		/* Test for being demotable */
>  		if (!test_and_set_bit(GLF_LOCK, &gl->gl_flags)) {
>  			gfs2_glock_hold(gl);
>