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 <[email protected]>

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

fs/gfs2/incore.h +2 -0

@@ -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;
 

fs/gfs2/glock.c +1 -0

@@ -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);

Quoted 9 lines

(quoted diff) +1 -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);
 	}

Review static int rq_demote(struct gfs2_glock * · line 583

Quoted 5 lines

(quoted diff) +2 -0

+
+	clear_bit(GLF_DEMOTE_IN_PROGRESS, &gl->gl_flags);
 	spin_lock(&gl->gl_spin);
 
 

May want to move the clear_bit inside the spin_lock so you don't end up having the same race where we clear the bit while inside handle_callback.