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[Cluster-devel] [GFS2 PATCH] Handle multiple glock demote requests



Red Hat bugzilla 295641... Wendy



Fix a race condition where multiple glock demote requests are sent to 
a node back-to-back. This patch does a check inside handle_callback() 
to see whether a demote request is in progress. If true, it sets a flag 
to make sure run_queue() will loop again to handle the new request, 
instead of erroneously setting gl_demote_state to a different state.

Signed-off-by: S. Wendy Cheng <wcheng redhat com>

 glock.c  |   13 ++++++++++++-
 incore.h |    2 ++
 2 files changed, 14 insertions(+), 1 deletion(-)

--- e48-brew/fs/gfs2/incore.h	2007-09-20 17:29:00.000000000 -0500
+++ e48/fs/gfs2/incore.h	2007-10-02 16:45:38.000000000 -0500
@@ -171,6 +171,7 @@ enum {
 	GLF_DEMOTE		= 3,
 	GLF_PENDING_DEMOTE	= 4,
 	GLF_DIRTY		= 5,
+	GLF_DEMOTE_IN_PROGRESS	= 6,
 };
 
 struct gfs2_glock {
@@ -190,6 +191,7 @@ struct gfs2_glock {
 	struct list_head gl_holders;
 	struct list_head gl_waiters1;	/* HIF_MUTEX */
 	struct list_head gl_waiters3;	/* HIF_PROMOTE */
+	int gl_waiters2;		/* GIF_DEMOTE */
 
 	const struct gfs2_glock_operations *gl_ops;
 
--- e48-brew/fs/gfs2/glock.c	2007-09-18 11:26:53.000000000 -0500
+++ e48/fs/gfs2/glock.c	2007-10-02 18:19:12.000000000 -0500
@@ -567,6 +567,7 @@ static int rq_demote(struct gfs2_glock *
 		return 0;
 	}
 	set_bit(GLF_LOCK, &gl->gl_flags);
+	set_bit(GLF_DEMOTE_IN_PROGRESS, &gl->gl_flags);
 	if (gl->gl_demote_state == LM_ST_UNLOCKED ||
 	    gl->gl_state != LM_ST_EXCLUSIVE) {
 		spin_unlock(&gl->gl_spin);
@@ -575,6 +576,8 @@ static int rq_demote(struct gfs2_glock *
 		spin_unlock(&gl->gl_spin);
 		gfs2_glock_xmote_th(gl, NULL);
 	}
+
+	clear_bit(GLF_DEMOTE_IN_PROGRESS, &gl->gl_flags);
 	spin_lock(&gl->gl_spin);
 
 	return 0;
@@ -605,6 +608,11 @@ static void run_queue(struct gfs2_glock 
 
 		} else if (test_bit(GLF_DEMOTE, &gl->gl_flags)) {
 			blocked = rq_demote(gl);
+			if (gl->gl_waiters2 && !blocked) {
+				set_bit(GLF_DEMOTE, &gl->gl_flags);
+				gl->gl_demote_state = LM_ST_UNLOCKED;
+			}
+			gl->gl_waiters2 = 0;
 		} else if (!list_empty(&gl->gl_waiters3)) {
 			gh = list_entry(gl->gl_waiters3.next,
 					struct gfs2_holder, gh_list);
@@ -721,7 +729,10 @@ static void handle_callback(struct gfs2_
 		}
 	} else if (gl->gl_demote_state != LM_ST_UNLOCKED &&
 			gl->gl_demote_state != state) {
-		gl->gl_demote_state = LM_ST_UNLOCKED;
+		if (test_bit(GLF_DEMOTE_IN_PROGRESS,  &gl->gl_flags)) 
+			gl->gl_waiters2 = 1;
+		else 
+			gl->gl_demote_state = LM_ST_UNLOCKED;
 	}
 	spin_unlock(&gl->gl_spin);
 }

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