[PATCH] x86: all cpu backtrace

When a spinlock lockup occurs, arrange for the NMI code to emit an all-cpu
backtrace, so we get to see which CPU is holding the lock, and where.

Cc: Andi Kleen <ak@muc.de>
Cc: Ingo Molnar <mingo@elte.hu>
Cc: Badari Pulavarty <pbadari@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Andi Kleen <ak@suse.de>

lib/spinlock_debug.c

@@ -7,6 +7,7 @@
  */
 
 #include <linux/spinlock.h>
+#include <linux/nmi.h>
 #include <linux/interrupt.h>
 #include <linux/debug_locks.h>
 #include <linux/delay.h>
@@ -117,6 +118,9 @@ static void __spin_lock_debug(spinlock_t *lock)
 				raw_smp_processor_id(), current->comm,
 				current->pid, lock);
 			dump_stack();
+#ifdef CONFIG_SMP
+			trigger_all_cpu_backtrace();
+#endif
 		}
 	}
 }