[PATCH] Avoid recursion in lockdep when stack tracer takes locks

The new dwarf2 unwinder needs to take locks to do backtraces
inside modules. This patch makes sure lockdep which calls
stacktrace is not reentered.

Thanks to Ingo for suggesting this simpler approach.

Cc: mingo@elte.hu
Signed-off-by: NAndi Kleen <ak@suse.de>

kernel/lockdep.c

@@ -227,7 +227,11 @@ static int save_trace(struct stack_trace *trace)
 	trace->skip = 3;
 	trace->all_contexts = 0;
 
+	/* Make sure to not recurse in case the the unwinder needs to tak
+e	   locks. */
+	lockdep_off();
 	save_stack_trace(trace, NULL);
+	lockdep_on();
 
 	trace->max_entries = trace->nr_entries;