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

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Date:   Thu,  9 Apr 2020 17:38:16 +0800
From:   Wang Qing <wangqing@...o.com>
To:     Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        James Morse <james.morse@....com>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Wang Qing <wangqing@...o.com>,
        jinho lim <jordan.lim@...sung.com>,
        Dave Martin <Dave.Martin@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     opensource.kernel@...o.com
Subject: [PATCH] ARM64: fixed dump_backtrace() when task running on another cpu

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@...o.com>
---
 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