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

[Bob Peterson <rpeterso@redhat.com>]

----- "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