linux-kernel - Re: [PATCH] ARM: Fix deadlock scenario with smp_send

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Message-ID: <504F7E3A.8020808@codeaurora.org>
Date:	Tue, 11 Sep 2012 11:08:58 -0700
From:	Stephen Boyd <sboyd@...eaurora.org>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] ARM: Fix deadlock scenario with smp_send_stop()

On 09/05/12 14:01, Stephen Boyd wrote:
> If one process calls sys_reboot and that process then stops other
> CPUs while those CPUs are within a spin_lock() region we can
> potentially encounter a deadlock scenario like below.
>
> CPU 0                   CPU 1
> -----                   -----
>                         spin_lock(my_lock)
> smp_send_stop()
>  send_IPI               handle_IPI()
>                          disable_preemption/irqs
>                           while(1);
>  <PREEMPT>
> spin_lock(my_lock) <--- Waits forever
>
> We shouldn't attempt to run any other tasks after we send a stop
> IPI to a CPU so disable preemption so that the reboot task runs to
> completion.
>
> Reported-by: Sundarajan Srinivasan <sundaraj@...eaurora.com>
> Signed-off-by: Stephen Boyd <sboyd@...eaurora.org>
> ---
>
> Unfortunately this won't fix the other problem I mentioned two weeks
> ago where smp_send_stop races with other CPUs calling cpu_up().

Any comments?

>
>  arch/arm/kernel/process.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
> index 693b744..663a7a8 100644
> --- a/arch/arm/kernel/process.c
> +++ b/arch/arm/kernel/process.c
> @@ -239,6 +239,7 @@ __setup("reboot=", reboot_setup);
>  
>  void machine_shutdown(void)
>  {
> +	preempt_disable();
>  #ifdef CONFIG_SMP
>  	smp_send_stop();
>  #endif


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