ARM: allow unwinder to unwind recursive functions

Allow the unwinder to unwind recursive functions if the stack makes
progress, even if the PC is the same. This allows tracing through
recursive __switchdev_handle_port_attr_set() and similar.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

arch/arm/kernel/unwind.c

@@ -444,7 +444,7 @@ int unwind_frame(struct stackframe *frame)
 		ctrl.vrs[PC] = ctrl.vrs[LR];
 
 	/* check for infinite loop */
-	if (frame->pc == ctrl.vrs[PC])
+	if (frame->pc == ctrl.vrs[PC] && frame->sp == ctrl.vrs[SP])
 		return -URC_FAILURE;
 
 	frame->fp = ctrl.vrs[FP];