[PATCH] ARM64: fixed dump_backtrace() when task running on another cpu

[Wang Qing]

We cannot get FP and PC when the task is running on another CPU,
task->thread.cpu_context is the last time the task was switched out,
it's better to give a reminder than to provide wrong information.

Signed-off-by: Wang Qing <wangqing@xxxxxxxx>
---
 arch/arm64/kernel/traps.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index cf402be..c04e3e8 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -106,6 +106,14 @@ void dump_backtrace(struct pt_regs *regs, struct task_struct *tsk)
 		start_backtrace(&frame,
 				(unsigned long)__builtin_frame_address(0),
 				(unsigned long)dump_backtrace);
+	} else if (tsk->on_cpu) {
+		/*
+		 * The task is running in another cpu, so the call stack
+		 * is changing and we cannot get it.
+		 */
+		pr_warn("tsk: %s is running in CPU%d, Don't call trace!\n",
+			tsk->comm, tsk->cpu);
+		return;
 	} else {
 		/*
 		 * task blocked in __switch_to
-- 
2.7.4