gfs2: Unlock fewer glocks on unmount

At unmount time, we would generally like to explicitly unlock as few
glocks as possible for efficiency.  We are already skipping glocks that
don't have a lock value block (LVB), but we can also skip glocks which
are not held in DLM_LOCK_EX or DLM_LOCK_PW mode (of which gfs2 only uses
DLM_LOCK_EX under the name LM_ST_EXCLUSIVE).
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>
Cc: David Teigland <teigland@redhat.com>

fs/gfs2/lock_dlm.c

@@ -316,10 +316,16 @@ static void gdlm_put_lock(struct gfs2_glock *gl)
 		gfs2_glock_free(gl);
 		return;
 	}
-	/* don't want to skip dlm_unlock writing the lvb when lock has one */
+
+	/*
+	 * When the lockspace is released, all remaining glocks will be
+	 * unlocked automatically.  This is more efficient than unlocking them
+	 * individually, but when the lock is held in DLM_LOCK_EX or
+	 * DLM_LOCK_PW mode, the lock value block (LVB) will be lost.
+	 */
 
 	if (test_bit(SDF_SKIP_DLM_UNLOCK, &sdp->sd_flags) &&
-	    !gl->gl_lksb.sb_lvbptr) {
+	    (!gl->gl_lksb.sb_lvbptr || gl->gl_state != LM_ST_EXCLUSIVE)) {
 		gfs2_glock_free_later(gl);
 		return;
 	}