[GFS2] Handle multiple glock demote requests

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 erronously setting gl_demote_state to a different state.

Signed-off-by: S. Wendy Cheng <wcheng@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>

2 files changed, 16 insertions, 1 deletions

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index a37efe4aae6f..104e83ff874f 100644
--- a/fs/gfs2/glock.c
+++ b/fs/gfs2/glock.c
@@ -567,7 +567,10 @@ static int rq_demote(struct gfs2_glock *gl)
                 gfs2_demote_wake(gl);
                 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);
@@ -576,7 +579,9 @@ static int rq_demote(struct gfs2_glock *gl)
                 spin_unlock(&gl->gl_spin);
                 gfs2_glock_xmote_th(gl, NULL);
         }
+
         spin_lock(&gl->gl_spin);
+        clear_bit(GLF_DEMOTE_IN_PROGRESS, &gl->gl_flags);
 
         return 0;
 }
@@ -606,6 +611,11 @@ static void run_queue(struct gfs2_glock *gl)
 
                 } 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);
@@ -722,7 +732,10 @@ static void handle_callback(struct gfs2_glock *gl, unsigned int state,
                 }
         } 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);
 }
diff --git a/fs/gfs2/incore.h b/fs/gfs2/incore.h
index eaddfb5a8e6f..662182bfbff7 100644
--- a/fs/gfs2/incore.h
+++ b/fs/gfs2/incore.h
@@ -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;