--- dahdi-linux/drivers/dahdi/dahdi-base.c	2013-01-17 17:54:19.803393313 +0700
+++ dahdi-linux-pavel/drivers/dahdi/dahdi-base.c	2013-01-18 16:45:29.004077678 +0700
@@ -173,7 +173,7 @@
 static sumtype *conf_sums;
 static sumtype *conf_sums_prev;
 
-static struct dahdi_span *master;
+static struct dahdi_span *master = NULL;
 struct file_operations *dahdi_transcode_fops = NULL;
 
 #ifdef CONFIG_DAHDI_CORE_TIMER
@@ -3802,31 +3802,28 @@
 
 static void __dahdi_find_master_span(void)
 {
-	struct dahdi_span *s;
+	struct dahdi_span *s, *old_master, *new_master = NULL;
 	unsigned long flags;
-	struct dahdi_span *old_master;
 
 	spin_lock_irqsave(&chan_lock, flags);
 	old_master = master;
-	list_for_each_entry(s, &span_list, spans_node) {
-		if (s->alarms && old_master)
+	/* Searching for the FIRST reliable sync source with reverse for. */
+	list_for_each_entry_reverse(s, &span_list, spans_node) {
+		if (!can_provide_timing(s) || s->alarms)
 			continue;
 		if (dahdi_is_digital_span(s) &&
-		    !test_bit(DAHDI_FLAGBIT_RUNNING, &s->flags) &&
-		    old_master)
-			continue;
-		if (!can_provide_timing(s))
+		    !test_bit(DAHDI_FLAGBIT_RUNNING, &s->flags))
 			continue;
-		if (master == s)
-			continue;
-
-		master = s;
-		break;
+		if ((0 == s->channels) && !new_master)	/* dummy is better than nothing (coretimer). */
+			new_master = s;
+		new_master = s;	/* But real span is better than dummy. */
 	}
+	master = new_master;
 	spin_unlock_irqrestore(&chan_lock, flags);
 
 	if ((debug & DEBUG_MAIN) && (old_master != master))
-		module_printk(KERN_NOTICE, "Master changed to %s\n", s->name);
+		module_printk(KERN_NOTICE, "Master changed to '%s'\n",
+			      master ? master->name : "core_timer");
 }
 
 #if LINUX_VERSION_CODE < KERNEL_VERSION(2, 6, 20)
@@ -7250,7 +7247,6 @@
 static int _dahdi_unassign_span(struct dahdi_span *span)
 {
 	int x;
-	struct dahdi_span *new_master, *s;
 	unsigned long flags;
 
 	if (!test_bit(DAHDI_FLAGBIT_REGISTERED, &span->flags)) {
@@ -7281,25 +7277,7 @@
 	for (x=0;x<span->channels;x++)
 		dahdi_chan_unreg(span->chans[x]);
 
-	new_master = master; /* FIXME: locking */
-	if (master == span)
-		new_master = NULL;
-
-	spin_lock_irqsave(&chan_lock, flags);
-	list_for_each_entry(s, &span_list, spans_node) {
-		if ((s == new_master) || !can_provide_timing(s))
-			continue;
-		new_master = s;
-		break;
-	}
-	spin_unlock_irqrestore(&chan_lock, flags);
-	if (master != new_master) {
-		if (debug & DEBUG_MAIN) {
-			module_printk(KERN_NOTICE, "%s: Span ('%s') is new master\n", __FUNCTION__,
-				      (new_master)? new_master->name: "no master");
-		}
-	}
-	master = new_master;
+        __dahdi_find_master_span();
 	return 0;
 }
 
@@ -9775,6 +9753,7 @@
 		 * dahdi_receive, and therefore the core of dahdi needs to
 		 * perform the master span processing itself. */
 		if (core_timer.dahdi_receive_used) {
+			master = NULL;
 			core_timer.dahdi_receive_used = 0;
 			dahdi_dbg(GENERAL, "Master changed to core_timer\n");
 		}