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

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Message-Id: <1587208459-5470-1-git-send-email-wangqing@vivo.com>
Date:   Sat, 18 Apr 2020 19:14:18 +0800
From:   Wang Qing <wangqing@...o.com>
To:     Russell King <linux@...linux.org.uk>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Enrico Weigelt <info@...ux.net>,
        Allison Randal <allison@...utok.net>,
        Wang Qing <wangqing@...o.com>,
        Vincent Whitchurch <vincent.whitchurch@...s.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Cc:     opensource.kernel@...o.com
Subject: [PATCH] arm: fixed backtrace when task running on another cpu

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@...o.com>
---
 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