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>

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index a3f90ad..f455a03 100644 (file)
--- 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);