[PATCH] arm: fixed backtrace when task running on another cpu

[Wang Qing]

We cannot get FP when the task is currently running on another CPU,
in this case, current stack is printed instead of the task.
Also, thread_saved_fp() is the last time the task was switched out,
we should not use too.

Signed-off-by: Wang Qing <wangqing@xxxxxxxx>
---
 arch/arm/kernel/traps.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/arch/arm/kernel/traps.c b/arch/arm/kernel/traps.c
index 1e70e72..24e860a 100644
--- a/arch/arm/kernel/traps.c
+++ b/arch/arm/kernel/traps.c
@@ -222,6 +222,9 @@ static void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
 	} else if (tsk != current) {
 		fp = thread_saved_fp(tsk);
 		mode = 0x10;
+	} else if (task_curr(tsk))
+		pr_info("tsk is running on another CPU, not trace!\n");
+		fp = 0;
 	} else {
 		asm("mov %0, fp" : "=r" (fp) : : "cc");
 		mode = 0x10;
-- 
2.7.4