[Cluster-devel] [PATCH 3/8] gfs2: Clean up glock work enqueuing

[Andreas Gruenbacher <agruenba@redhat.com>]

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
---
 fs/gfs2/glock.c | 102 +++++++++++++++++++++++++++++++++-----------------------
 1 file changed, 61 insertions(+), 41 deletions(-)

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index 959a19c..6d7147c8 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -152,6 +152,29 @@ static void gfs2_glock_remove_from_lru(struct gfs2_glock *gl)
 	spin_unlock(&lru_lock);
 }
 
+/*
+ * Enqueue the glock on the work queue.  Passes one glock reference on to the
+ * work queue.
+ */
+static void __gfs2_glock_queue_work(struct gfs2_glock *gl, unsigned long delay) {
+	if (!queue_delayed_work(glock_workqueue, &gl->gl_work, delay)) {
+		/*
+		 * We are holding the lockref spinlock, and the work was still
+		 * queued above.  The queued work (glock_work_func) takes that
+		 * spinlock before dropping its glock reference(s), so it
+		 * cannot have dropped them in the meantime.
+		 */
+		GLOCK_BUG_ON(gl, gl->gl_lockref.count < 2);
+		gl->gl_lockref.count--;
+	}
+}
+
+static void gfs2_glock_queue_work(struct gfs2_glock *gl, unsigned long delay) {
+	spin_lock(&gl->gl_lockref.lock);
+	__gfs2_glock_queue_work(gl, delay);
+	spin_unlock(&gl->gl_lockref.lock);
+}
+
 /**
  * gfs2_glock_put() - Decrement reference count on glock
  * @gl: The glock to put
@@ -482,8 +505,7 @@ __acquires(&gl->gl_lockref.lock)
 		    target == LM_ST_UNLOCKED &&
 		    test_bit(SDF_SKIP_DLM_UNLOCK, &sdp->sd_flags)) {
 			finish_xmote(gl, target);
-			if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0)
-				gfs2_glock_put(gl);
+			gfs2_glock_queue_work(gl, 0);
 		}
 		else if (ret) {
 			pr_err("lm_lock ret %d\n", ret);
@@ -492,8 +514,7 @@ __acquires(&gl->gl_lockref.lock)
 		}
 	} else { /* lock_nolock */
 		finish_xmote(gl, target);
-		if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0)
-			gfs2_glock_put(gl);
+		gfs2_glock_queue_work(gl, 0);
 	}
 
 	spin_lock(&gl->gl_lockref.lock);
@@ -565,8 +586,7 @@ __acquires(&gl->gl_lockref.lock)
 	clear_bit(GLF_LOCK, &gl->gl_flags);
 	smp_mb__after_atomic();
 	gl->gl_lockref.count++;
-	if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0)
-		gl->gl_lockref.count--;
+	__gfs2_glock_queue_work(gl, 0);
 	return;
 
 out_unlock:
@@ -601,11 +621,11 @@ 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;
+	unsigned int drop_refs = 1;
 
 	if (test_and_clear_bit(GLF_REPLY_PENDING, &gl->gl_flags)) {
 		finish_xmote(gl, gl->gl_reply);
-		drop_ref = 1;
+		drop_refs++;
 	}
 	spin_lock(&gl->gl_lockref.lock);
 	if (test_bit(GLF_PENDING_DEMOTE, &gl->gl_flags) &&
@@ -623,16 +643,25 @@ static void glock_work_func(struct work_struct *work)
 		}
 	}
 	run_queue(gl, 0);
-	spin_unlock(&gl->gl_lockref.lock);
-	if (!delay)
-		gfs2_glock_put(gl);
-	else {
+	if (delay) {
+		/* Keep one glock reference for the work we requeue. */
+		drop_refs--;
 		if (gl->gl_name.ln_type != LM_TYPE_INODE)
 			delay = 0;
-		if (queue_delayed_work(glock_workqueue, &gl->gl_work, delay) == 0)
-			gfs2_glock_put(gl);
+		__gfs2_glock_queue_work(gl, delay);
+	}
+	if (drop_refs > 1) {
+		gl->gl_lockref.count -= drop_refs - 1;
+		drop_refs = 1;
 	}
-	if (drop_ref)
+	spin_unlock(&gl->gl_lockref.lock);
+
+	/*
+	 * Drop the remaining glock reference after grabbing (and releasing)
+	 * the lockref spinlock: this allows tasks to safely drop glock
+	 * references under that spinlock (see __gfs2_glock_queue_work).
+	 */
+	if (drop_refs)
 		gfs2_glock_put(gl);
 }
 
@@ -986,8 +1015,7 @@ int gfs2_glock_nq(struct gfs2_holder *gh)
 		     test_and_clear_bit(GLF_FROZEN, &gl->gl_flags))) {
 		set_bit(GLF_REPLY_PENDING, &gl->gl_flags);
 		gl->gl_lockref.count++;
-		if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0)
-			gl->gl_lockref.count--;
+		__gfs2_glock_queue_work(gl, 0);
 	}
 	run_queue(gl, 1);
 	spin_unlock(&gl->gl_lockref.lock);
@@ -1047,17 +1075,15 @@ void gfs2_glock_dq(struct gfs2_holder *gh)
 		gfs2_glock_add_to_lru(gl);
 
 	trace_gfs2_glock_queue(gh, 0);
+	if (unlikely(!fast_path)) {
+		gl->gl_lockref.count++;
+		if (test_bit(GLF_PENDING_DEMOTE, &gl->gl_flags) &&
+		    !test_bit(GLF_DEMOTE, &gl->gl_flags) &&
+		    gl->gl_name.ln_type == LM_TYPE_INODE)
+			delay = gl->gl_hold_time;
+		__gfs2_glock_queue_work(gl, delay);
+	}
 	spin_unlock(&gl->gl_lockref.lock);
-	if (likely(fast_path))
-		return;
-
-	gfs2_glock_hold(gl);
-	if (test_bit(GLF_PENDING_DEMOTE, &gl->gl_flags) &&
-	    !test_bit(GLF_DEMOTE, &gl->gl_flags) &&
-	    gl->gl_name.ln_type == LM_TYPE_INODE)
-		delay = gl->gl_hold_time;
-	if (queue_delayed_work(glock_workqueue, &gl->gl_work, delay) == 0)
-		gfs2_glock_put(gl);
 }
 
 void gfs2_glock_dq_wait(struct gfs2_holder *gh)
@@ -1233,9 +1259,8 @@ void gfs2_glock_cb(struct gfs2_glock *gl, unsigned int state)
 
 	spin_lock(&gl->gl_lockref.lock);
 	handle_callback(gl, state, delay, true);
+	__gfs2_glock_queue_work(gl, delay);
 	spin_unlock(&gl->gl_lockref.lock);
-	if (queue_delayed_work(glock_workqueue, &gl->gl_work, delay) == 0)
-		gfs2_glock_put(gl);
 }
 
 /**
@@ -1294,10 +1319,8 @@ void gfs2_glock_complete(struct gfs2_glock *gl, int ret)
 
 	gl->gl_lockref.count++;
 	set_bit(GLF_REPLY_PENDING, &gl->gl_flags);
+	__gfs2_glock_queue_work(gl, 0);
 	spin_unlock(&gl->gl_lockref.lock);
-
-	if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0)
-		gfs2_glock_put(gl);
 }
 
 static int glock_cmp(void *priv, struct list_head *a, struct list_head *b)
@@ -1355,8 +1378,7 @@ __acquires(&lru_lock)
 		if (demote_ok(gl))
 			handle_callback(gl, LM_ST_UNLOCKED, 0, false);
 		WARN_ON(!test_and_clear_bit(GLF_LOCK, &gl->gl_flags));
-		if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0)
-			gl->gl_lockref.count--;
+		__gfs2_glock_queue_work(gl, 0);
 		spin_unlock(&gl->gl_lockref.lock);
 		cond_resched_lock(&lru_lock);
 	}
@@ -1462,13 +1484,12 @@ static void glock_hash_walk(glock_examiner examiner, const struct gfs2_sbd *sdp)
 
 static void thaw_glock(struct gfs2_glock *gl)
 {
-	if (!test_and_clear_bit(GLF_FROZEN, &gl->gl_flags))
-		goto out;
-	set_bit(GLF_REPLY_PENDING, &gl->gl_flags);
-	if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0) {
-out:
+	if (!test_and_clear_bit(GLF_FROZEN, &gl->gl_flags)) {
 		gfs2_glock_put(gl);
+		return;
 	}
+	set_bit(GLF_REPLY_PENDING, &gl->gl_flags);
+	gfs2_glock_queue_work(gl, 0);
 }
 
 /**
@@ -1484,9 +1505,8 @@ static void clear_glock(struct gfs2_glock *gl)
 	spin_lock(&gl->gl_lockref.lock);
 	if (gl->gl_state != LM_ST_UNLOCKED)
 		handle_callback(gl, LM_ST_UNLOCKED, 0, false);
+	__gfs2_glock_queue_work(gl, 0);
 	spin_unlock(&gl->gl_lockref.lock);
-	if (queue_delayed_work(glock_workqueue, &gl->gl_work, 0) == 0)
-		gfs2_glock_put(gl);
 }
 
 /**
-- 
2.7.4