[PATCH] x86-64: dump_trace() atomicity fix

Fix

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

in backtracer on preemptible debug kernels.

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

1 files changed, 5 insertions, 3 deletions

diff --git a/arch/x86_64/kernel/traps.c b/arch/x86_64/kernel/traps.c
index eedd4e759c3a..e37b4d77d5a8 100644
--- a/arch/x86_64/kernel/traps.c
+++ b/arch/x86_64/kernel/traps.c
@@ -254,7 +254,7 @@ void dump_trace(struct task_struct *tsk, struct pt_regs *regs,
                 unsigned long *stack,
                 struct stacktrace_ops *ops, void *data)
 {
-        const unsigned cpu = smp_processor_id();
+        const unsigned cpu = get_cpu();
         unsigned long *irqstack_end = (unsigned long*)cpu_pda(cpu)->irqstackptr;
         unsigned used = 0;
         struct thread_info *tinfo;
@@ -286,11 +286,11 @@ void dump_trace(struct task_struct *tsk, struct pt_regs *regs,
                                         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
@@ -385,6 +385,8 @@ void dump_trace(struct task_struct *tsk, struct pt_regs *regs,
         tinfo = current_thread_info();
         HANDLE_STACK (valid_stack_ptr(tinfo, stack));
 #undef HANDLE_STACK
+out:
+        put_cpu();
 }
 EXPORT_SYMBOL(dump_trace);