linux-kernel - Re: [tip:smp/hotplug] cpu/hotplug: Abort disabling secondary CPUs if wakeup is pending

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Message-ID: <20200330194014.lwpmbv2zekfk6ywx@e107158-lin.cambridge.arm.com>
Date:   Mon, 30 Mar 2020 20:40:14 +0100
From:   Qais Yousef <qais.yousef@....com>
To:     Thomas Gleixner <tglx@...utronix.de>
Cc:     Boqun Feng <boqun.feng@...il.com>, peterz@...radead.org,
        linux-kernel@...r.kernel.org, len.brown@...el.com,
        pkondeti@...eaurora.org, jpoimboe@...hat.com, pavel@....cz,
        konrad.wilk@...cle.com, mojha@...eaurora.org, jkosina@...e.cz,
        mingo@...nel.org, hpa@...or.com, rjw@...ysocki.net,
        linux-tip-commits@...r.kernel.org
Subject: Re: [tip:smp/hotplug] cpu/hotplug: Abort disabling secondary CPUs if
 wakeup is pending

On 03/27/20 12:06, Thomas Gleixner wrote:
> Boqun Feng <boqun.feng@...il.com> writes:
> > From the commit message, it makes sense to add the pm_wakeup_pending()
> > check if freeze_secondary_cpus() is used for system suspend. However,
> > freeze_secondary_cpus() is also used in kexec path on arm64:
> 
> Bah!
> 
> > 	kernel_kexec():
> > 	  machine_shutdown():
> > 	    disable_nonboot_cpus():
> > 	      freeze_secondary_cpus()
> >
> > , so I wonder whether the pm_wakeup_pending() makes sense in this
> > situation? Because IIUC, in this case we want to reboot the system
> > regardlessly, the pm_wakeup_pending() checking seems to be inappropriate
> > then.
> 
> Fix below.
> 
> Thanks,
> 
>         tglx
> 
> 8<------------
> 
> --- a/include/linux/cpu.h
> +++ b/include/linux/cpu.h
> @@ -133,12 +133,18 @@ static inline void get_online_cpus(void)
>  static inline void put_online_cpus(void) { cpus_read_unlock(); }
>  
>  #ifdef CONFIG_PM_SLEEP_SMP
> -extern int freeze_secondary_cpus(int primary);
> +int __freeze_secondary_cpus(int primary, bool suspend);
> +static inline int freeze_secondary_cpus(int primary)
> +{
> +	return __freeze_secondary_cpus(primary, true);
> +}
> +
>  static inline int disable_nonboot_cpus(void)
>  {
> -	return freeze_secondary_cpus(0);
> +	return __freeze_secondary_cpus(0, false);
>  }

If I read the code correctly, arch/x86/power/cpu.c is calling
disable_nonboot_cpus() from suspend resume, which is the only user in
tip/smp/core after my series.

This means you won't abort a suspend/hibernate if a late wakeup source happens?
Or it might just mean that we'll wakeup slightly later than we would have done.

Anyways. I think it would be better to kill off disable_nonboot_cpus() and
directly call freeze_nonboot_cpus() in x86/power/cpu.c.

I'd be happy to send a patch for this.

Assuming that x86 is okay with the late(r) abort, this patch could stay as-is
for stable trees. Otherwise, maybe we need to revert this and look for another
option for stable trees?

Thanks

--
Qais Yousef

> -extern void enable_nonboot_cpus(void);
> +
> +void enable_nonboot_cpus(void);
>  
>  static inline int suspend_disable_secondary_cpus(void)
>  {
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -1200,7 +1200,7 @@ EXPORT_SYMBOL_GPL(cpu_up);
>  #ifdef CONFIG_PM_SLEEP_SMP
>  static cpumask_var_t frozen_cpus;
>  
> -int freeze_secondary_cpus(int primary)
> +int __freeze_secondary_cpus(int primary, bool suspend)
>  {
>  	int cpu, error = 0;
>  
> @@ -1225,7 +1225,7 @@ int freeze_secondary_cpus(int primary)
>  		if (cpu == primary)
>  			continue;
>  
> -		if (pm_wakeup_pending()) {
> +		if (suspend && pm_wakeup_pending()) {
>  			pr_info("Wakeup pending. Abort CPU freeze\n");
>  			error = -EBUSY;
>  			break;