From: Mark Rutland <mark.rutland@arm.com>
To: Wang Qing <wangqing@vivo.com>
Cc: opensource.kernel@vivo.com,
Catalin Marinas <catalin.marinas@arm.com>,
linux-kernel@vger.kernel.org, jinho lim <jordan.lim@samsung.com>,
James Morse <james.morse@arm.com>,
"Eric W. Biederman" <ebiederm@xmission.com>,
Thomas Gleixner <tglx@linutronix.de>,
Will Deacon <will@kernel.org>, Dave Martin <Dave.Martin@arm.com>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH] ARM64: fixed dump_backtrace() when task running on another cpu
Date: Thu, 9 Apr 2020 11:40:16 +0100 [thread overview]
Message-ID: <20200409104016.GA2183@C02TD0UTHF1T.local> (raw)
In-Reply-To: <1586425106-7369-1-git-send-email-wangqing@vivo.com>
Hi,
On Thu, Apr 09, 2020 at 05:38:16PM +0800, Wang Qing wrote:
> 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@vivo.com>
Are you seeing this happen anywhere in particular today?
> ---
> 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);
I believe that we can race with a concurrent write to tsk->cpu in both
cases above. We could use READ_ONCE() to get a snapshot, but we can
still race and miss cases where the task was runnning as we backtrace
it.
Thanks,
Mark.
> + return;
> } else {
> /*
> * task blocked in __switch_to
> --
> 2.7.4
>
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next prev parent reply other threads:[~2020-04-09 10:40 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-04-09 9:38 [PATCH] ARM64: fixed dump_backtrace() when task running on another cpu Wang Qing
2020-04-09 10:40 ` Mark Rutland [this message]
2020-04-13 9:23 ` Wang Qing
2020-04-14 12:54 ` [PATCH] " Mark Rutland
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