GFS2: Fix glock refcount issues

This patch fixes some ref counting issues. Firstly by moving
the point at which we drop the ref count after a dlm lock
operation has completed we ensure that we never call
gfs2_glock_hold() on a lock with a zero ref count.

Secondly, by using atomic_dec_and_lock() in gfs2_glock_put()
we ensure that at no time will a glock with zero ref count
appear on the lru_list. That means that we can remove the
check for this in our shrinker (which was racy).

Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

1 files changed, 8 insertions, 13 deletions

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index a3f90ad2af80..f455a03a09e2 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -241,15 +241,14 @@ int gfs2_glock_put(struct gfs2_glock *gl)
         int rv = 0;
 
         write_lock(gl_lock_addr(gl->gl_hash));
-        if (atomic_dec_and_test(&gl->gl_ref)) {
+        if (atomic_dec_and_lock(&gl->gl_ref, &lru_lock)) {
                 hlist_del(&gl->gl_list);
-                write_unlock(gl_lock_addr(gl->gl_hash));
-                spin_lock(&lru_lock);
                 if (!list_empty(&gl->gl_lru)) {
                         list_del_init(&gl->gl_lru);
                         atomic_dec(&lru_count);
                 }
                 spin_unlock(&lru_lock);
+                write_unlock(gl_lock_addr(gl->gl_hash));
                 GLOCK_BUG_ON(gl, !list_empty(&gl->gl_holders));
                 glock_free(gl);
                 rv = 1;
@@ -513,7 +512,6 @@ retry:
                         GLOCK_BUG_ON(gl, 1);
                 }
                 spin_unlock(&gl->gl_spin);
-                gfs2_glock_put(gl);
                 return;
         }
 
@@ -524,8 +522,6 @@ retry:
                 if (glops->go_xmote_bh) {
                         spin_unlock(&gl->gl_spin);
                         rv = glops->go_xmote_bh(gl, gh);
-                        if (rv == -EAGAIN)
-                                return;
                         spin_lock(&gl->gl_spin);
                         if (rv) {
                                 do_error(gl, rv);
@@ -540,7 +536,6 @@ out:
         clear_bit(GLF_LOCK, &gl->gl_flags);
 out_locked:
         spin_unlock(&gl->gl_spin);
-        gfs2_glock_put(gl);
 }
 
 static unsigned int gfs2_lm_lock(struct gfs2_sbd *sdp, void *lock,
@@ -600,7 +595,6 @@ __acquires(&gl->gl_spin)
 
         if (!(ret & LM_OUT_ASYNC)) {
                 finish_xmote(gl, ret);
-                gfs2_glock_hold(gl);
                 if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0)
                         gfs2_glock_put(gl);
         } else {
@@ -712,9 +706,12 @@ static void glock_work_func(struct work_struct *work)
 {
         unsigned long delay = 0;
         struct gfs2_glock *gl = container_of(work, struct gfs2_glock, gl_work.work);
+        int drop_ref = 0;
 
-        if (test_and_clear_bit(GLF_REPLY_PENDING, &gl->gl_flags))
+        if (test_and_clear_bit(GLF_REPLY_PENDING, &gl->gl_flags)) {
                 finish_xmote(gl, gl->gl_reply);
+                drop_ref = 1;
+        }
         down_read(&gfs2_umount_flush_sem);
         spin_lock(&gl->gl_spin);
         if (test_and_clear_bit(GLF_PENDING_DEMOTE, &gl->gl_flags) &&
@@ -732,6 +729,8 @@ static void glock_work_func(struct work_struct *work)
         if (!delay ||
             queue_delayed_work(glock_workqueue, &gl->gl_work, delay) == 0)
                 gfs2_glock_put(gl);
+        if (drop_ref)
+                gfs2_glock_put(gl);
 }
 
 /**
@@ -1366,10 +1365,6 @@ static int gfs2_shrink_glock_memory(int nr, gfp_t gfp_mask)
                 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);