Patch "gfs2: Fix glock rhashtable rcu bug" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

gfs2: Fix glock rhashtable rcu bug

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
gfs2-fix-glock-rhashtable-rcu-bug.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Andreas Gruenbacher <[email protected]>
Date: Fri, 7 Jul 2017 13:22:05 -0500
Subject: gfs2: Fix glock rhashtable rcu bug

From: Andreas Gruenbacher <[email protected]>

commit 961ae1d83d055a4b9ebbfb4cc8ca62ec1a7a3b74 upstream.

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.

---
 fs/gfs2/glock.c  |   11 +++++++++--
 fs/gfs2/incore.h |    1 +
 2 files changed, 10 insertions(+), 2 deletions(-)

@@ -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 *
 		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);
 }

@@ -367,6 +367,7 @@ struct gfs2_glock {
 			loff_t end;
 		} gl_vm;
 	};
+	struct rcu_head gl_rcu;
 	struct rhash_head gl_node;
 };
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/gfs2-fix-glock-rhashtable-rcu-bug.patch