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

[Andreas Gruenbacher <agruenba@redhat.com>]

On Thu, Jun 1, 2017 at 5:46 PM, Steven Whitehouse <swhiteho@redhat.com> wrote:
> [...] Can we not just have a version of gfs2_glock_put that takes
> the number of refs to drop in case that we really have to count them up like
> that?
>
> gfs2_glock_put_n(gl, drop_refs)

Not so easily: there is no function that would drop more than one reference
from a lockref, and adding one doesn't seem very economical.  We could
open-code the entire lockref dropping here though; it's not too horrible.

Thanks,
Andreas

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index 1e7b5f2..4733ec2 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -178,20 +178,11 @@ static void gfs2_glock_queue_work(struct gfs2_glock *gl, unsigned long delay) {
 	spin_unlock(&gl->gl_lockref.lock);
 }
 
-/**
- * gfs2_glock_put() - Decrement reference count on glock
- * @gl: The glock to put
- *
- */
-
-void gfs2_glock_put(struct gfs2_glock *gl)
+static void __gfs2_glock_put(struct gfs2_glock *gl)
 {
 	struct gfs2_sbd *sdp = gl->gl_name.ln_sbd;
 	struct address_space *mapping = gfs2_glock2aspace(gl);
 
-	if (lockref_put_or_lock(&gl->gl_lockref))
-		return;
-
 	lockref_mark_dead(&gl->gl_lockref);
 
 	spin_lock(&lru_lock);
@@ -206,6 +197,20 @@ void gfs2_glock_put(struct gfs2_glock *gl)
 }
 
 /**
+ * gfs2_glock_put() - Decrement reference count on glock
+ * @gl: The glock to put
+ *
+ */
+
+void gfs2_glock_put(struct gfs2_glock *gl)
+{
+	if (lockref_put_or_lock(&gl->gl_lockref))
+		return;
+
+	__gfs2_glock_put(gl);
+}
+
+/**
  * may_grant - check if its ok to grant a new lock
  * @gl: The glock
  * @gh: The lock request which we wish to grant
@@ -655,19 +660,18 @@ static void glock_work_func(struct work_struct *work)
 			delay = 0;
 		__gfs2_glock_queue_work(gl, delay);
 	}
-	if (drop_refs > 1) {
-		gl->gl_lockref.count -= drop_refs - 1;
-		drop_refs = 1;
-	}
-	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).
+	 * Drop the remaining glock references manually here. (Mind that
+	 * __gfs2_glock_queue_work depends on the lockref spinlock begin held
+	 * here as well.)
 	 */
-	if (drop_refs)
-		gfs2_glock_put(gl);
+	gl->gl_lockref.count -= drop_refs;
+	if (!gl->gl_lockref.count) {
+		__gfs2_glock_put(gl);
+		return;
+	}
+	spin_unlock(&gl->gl_lockref.lock);
 }
 
 /**