linux-kernel - Re: [PATCH] stop_machine: Mark functions as notrace

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Date:   Wed, 21 Oct 2020 17:58:15 -0700
From:   Atish Patra <atishp@...shpatra.org>
To:     Zong Li <zong.li@...ive.com>
Cc:     "Paul E. McKenney" <paulmck@...nel.org>, josh@...htriplett.org,
        rostedt@...dmis.org, mathieu.desnoyers@...icios.com,
        jiangshanlai@...il.com, joel@...lfernandes.org,
        vincent.whitchurch@...s.com, Thomas Gleixner <tglx@...utronix.de>,
        Paul Walmsley <paul.walmsley@...ive.com>,
        Palmer Dabbelt <palmerdabbelt@...gle.com>,
        Guo Ren <guoren@...nel.org>, mhiramat@...nel.org,
        Greentime Hu <greentime.hu@...ive.com>,
        Colin Ian King <colin.king@...onical.com>,
        rcu@...r.kernel.org,
        "linux-kernel@...r.kernel.org List" <linux-kernel@...r.kernel.org>,
        linux-riscv <linux-riscv@...ts.infradead.org>
Subject: Re: [PATCH] stop_machine: Mark functions as notrace

On Wed, Oct 21, 2020 at 12:38 AM Zong Li <zong.li@...ive.com> wrote:
>
> Like the commit cb9d7fd51d9f ("watchdog: Mark watchdog touch functions
> as notrace"), some architectures assume that the stopped CPUs don't make
> function calls to traceable functions when they are in the stopped
> state. For example, it causes unexpected kernel crashed when switching
> tracer on RISC-V.
>
> The following patches added calls to these two functions, fix it by
> adding the notrace annotations.
>
> Fixes: 4ecf0a43e729 ("processor: get rid of cpu_relax_yield")
> Fixes: 366237e7b083 ("stop_machine: Provide RCU quiescent state in
> multi_cpu_stop()")
>
> Signed-off-by: Zong Li <zong.li@...ive.com>
> ---
>  kernel/rcu/tree.c     | 2 +-
>  kernel/stop_machine.c | 2 +-
>  2 files changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 06895ef85d69..2a52f42f64b6 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -409,7 +409,7 @@ bool rcu_eqs_special_set(int cpu)
>   *
>   * The caller must have disabled interrupts and must not be idle.
>   */
> -void rcu_momentary_dyntick_idle(void)
> +notrace void rcu_momentary_dyntick_idle(void)
>  {
>         int special;
>
> diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
> index 865bb0228ab6..890b79cf0e7c 100644
> --- a/kernel/stop_machine.c
> +++ b/kernel/stop_machine.c
> @@ -178,7 +178,7 @@ static void ack_state(struct multi_stop_data *msdata)
>                 set_state(msdata, msdata->state + 1);
>  }
>
> -void __weak stop_machine_yield(const struct cpumask *cpumask)
> +notrace void __weak stop_machine_yield(const struct cpumask *cpumask)
>  {
>         cpu_relax();
>  }
> --
> 2.28.0
>

Thanks for the fix. FWIW,

Tested-by: Atish Patra <atish.patra@....com>

Can you update the bugzilla as well ?

https://bugzilla.kernel.org/show_bug.cgi?id=209317


--
Regards,
Atish