[Cluster-devel] [PATCH] gfs2: Fix glock rhashtable rcu bug

[Bob Peterson <rpeterso@redhat.com>]

----- Original Message -----
| Before commit 88ffbf3e03 "GFS2: Use resizable hash table for glocks",
| glocks were freed via call_rcu to allow reading the glock hashtable
| locklessly using rcu.  This was then changed to free glocks immediately,
| which made reading the glock hashtable unsafe.  Bring back the original
| code for freeing glocks via call_rcu.
| 
| Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
| Cc: stable at vger.kernel.org # 4.3
| ---
|  fs/gfs2/glock.c  | 11 +++++++++--
|  fs/gfs2/incore.h |  1 +
|  2 files changed, 10 insertions(+), 2 deletions(-)
| 
| diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
| index 6cd71c5..c38ab6c 100644
| --- a/fs/gfs2/glock.c
| +++ b/fs/gfs2/glock.c
| @@ -80,9 +80,9 @@ static struct rhashtable_params ht_parms = {
|  
|  static struct rhashtable gl_hash_table;
|  
| -void gfs2_glock_free(struct gfs2_glock *gl)
| +static void gfs2_glock_dealloc(struct rcu_head *rcu)
|  {
| -	struct gfs2_sbd *sdp = gl->gl_name.ln_sbd;
| +	struct gfs2_glock *gl = container_of(rcu, struct gfs2_glock, gl_rcu);
|  
|  	if (gl->gl_ops->go_flags & GLOF_ASPACE) {
|  		kmem_cache_free(gfs2_glock_aspace_cachep, gl);
| @@ -90,6 +90,13 @@ void gfs2_glock_free(struct gfs2_glock *gl)
|  		kfree(gl->gl_lksb.sb_lvbptr);
|  		kmem_cache_free(gfs2_glock_cachep, gl);
|  	}
| +}
| +
| +void gfs2_glock_free(struct gfs2_glock *gl)
| +{
| +	struct gfs2_sbd *sdp = gl->gl_name.ln_sbd;
| +
| +	call_rcu(&gl->gl_rcu, gfs2_glock_dealloc);
|  	if (atomic_dec_and_test(&sdp->sd_glock_disposal))
|  		wake_up(&sdp->sd_glock_wait);
|  }
| diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
| index 790e739..73fce76 100644
| --- a/fs/gfs2/incore.h
| +++ b/fs/gfs2/incore.h
| @@ -373,6 +373,7 @@ struct gfs2_glock {
|  			loff_t end;
|  		} gl_vm;
|  	};
| +	struct rcu_head gl_rcu;
|  	struct rhash_head gl_node;
|  };
|  
| --
| 2.7.5
Hi,

Thanks. This is now applied to the for-next branch of the linux-gfs2 tree:
https://git.kernel.org/pub/scm/linux/kernel/git/gfs2/linux-gfs2.git/commit/fs/gfs2?h=for-next&id=961ae1d83d055a4b9ebbfb4cc8ca62ec1a7a3b74

Next time, please cc cluster-devel.

This is important enough that I'm going to tag it and ask
to merge it right away.

Regards,

Bob Peterson
Red Hat File Systems