[PATCH] ARM: Fix deadlock scenario with smp_send_stop()

[Stephen Boyd]

On 07/09, 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 this task runs to
> completion.
> 
> Reported-by: Sundarajan Srinivasan <sundaraj at codeaurora.com>
> Signed-off-by: Stephen Boyd <sboyd at codeaurora.org>
> ---
> 
> Resending this patch now that the context has changed.

Ping? Shall I put this in the patch tracker?

> 
>  arch/arm/kernel/process.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/arm/kernel/process.c b/arch/arm/kernel/process.c
> index 7f1efcd..8bc12d7 100644
> --- a/arch/arm/kernel/process.c
> +++ b/arch/arm/kernel/process.c
> @@ -206,6 +206,7 @@ void machine_shutdown(void)
>   */
>  void machine_halt(void)
>  {
> +	preempt_disable();
>  	smp_send_stop();
>  
>  	local_irq_disable();
> @@ -220,6 +221,7 @@ void machine_halt(void)
>   */
>  void machine_power_off(void)
>  {
> +	preempt_disable();
>  	smp_send_stop();
>  
>  	if (pm_power_off)
> @@ -239,6 +241,7 @@ void machine_power_off(void)
>   */
>  void machine_restart(char *cmd)
>  {
> +	preempt_disable();
>  	smp_send_stop();
>  
>  	arm_pm_restart(reboot_mode, cmd);

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