[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>

diff --git a/fs/gfs2/glock.c b/fs/gfs2/glock.c
index a37efe4..104e83f 100644 (file)
--- 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 eaddfb5..662182b 100644 (file)
--- 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;