dump_trace() atomicity fix

From: Andrew Morton <akpm@osdl.org>

BUG: using smp_processor_id() in preemptible [00000001] code:

Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Andi Kleen <ak@suse.de>

---

 arch/x86_64/kernel/traps.c |   10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

Index: linux/arch/x86_64/kernel/traps.c
===================================================================
--- linux.orig/arch/x86_64/kernel/traps.c
+++ linux/arch/x86_64/kernel/traps.c
@@ -248,10 +248,12 @@ void dump_trace(struct task_struct *tsk,
 		unsigned long *stack,
 		struct stacktrace_ops *ops, void *data)
 {
-	const unsigned cpu = smp_processor_id();
+	unsigned cpu = get_cpu();
 	unsigned long *irqstack_end = (unsigned long*)cpu_pda(cpu)->irqstackptr;
 	unsigned used = 0;
 
+	irqstack_end = (unsigned long*)cpu_pda(cpu)->irqstackptr;
+
 	if (!tsk)
 		tsk = current;
 
@@ -279,11 +281,11 @@ void dump_trace(struct task_struct *tsk,
 					MSG("Leftover inexact backtrace:");
 					stack = (unsigned long *)UNW_SP(&info);
 					if (!stack)
-						return;
+						goto out;
 				} else
 					MSG("Full inexact backtrace again:");
 			} else if (call_trace >= 1)
-				return;
+				goto out;
 			else
 				MSG("Full inexact backtrace again:");
 		} else
@@ -371,6 +373,8 @@ void dump_trace(struct task_struct *tsk,
 	 */
 	HANDLE_STACK (((long) stack & (THREAD_SIZE-1)) != 0);
 #undef HANDLE_STACK
+out:
+	put_cpu();
 }
 EXPORT_SYMBOL(dump_trace);