[V3 1/3] ARM64:fixed dump_backtrace() when task running on another cpu

From: Wang Qing
Date: Tue Apr 14 2020 - 08:37:03 EST


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
for example when Task blocked in spinlock/interrupt/busy loop.

Signed-off-by: Wang Qing <wangqing@xxxxxxxx>
---
arch/arm64/kernel/traps.c | 7 +++++++
1 file changed, 7 insertions(+)

diff --git a/arch/arm64/kernel/traps.c b/arch/arm64/kernel/traps.c
index cf402be..c74090b 100644
--- a/arch/arm64/kernel/traps.c
+++ b/arch/arm64/kernel/traps.c
@@ -106,6 +106,13 @@ 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 (task_running(tsk)) {
+ /*
+ * The task is running in another cpu, we cannot get it.
+ */
+ pr_warn("tsk: %s is running in CPU%d, Don't call trace!\n",
+ tsk->comm, task_cpu(tsk));
+ return;
} else {
/*
* task blocked in __switch_to
--
2.7.4