linux-kernel - RE: [PATCH 1/4][RFC v2] PM / sleep: Avoid accessing frozen

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Date:	Sun, 26 Jun 2016 01:16:54 +0000
From:	"Chen, Yu C" <yu.c.chen@...el.com>
To:	Pavel Machek <pavel@....cz>
CC:	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"x86@...nel.org" <x86@...nel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Len Brown <lenb@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"H. Peter Anvin" <hpa@...or.com>, Borislav Petkov <bp@...e.de>,
	Brian Gerst <brgerst@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...nel.org>,
	Varun Koyyalagunta <cpudebug@...ttech.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/4][RFC v2] PM / sleep: Avoid accessing frozen_cpus if
 it is NULL

Hi,

> -----Original Message-----
> From: Pavel Machek [mailto:pavel@....cz]
> Sent: Sunday, June 26, 2016 12:51 AM
> To: Chen, Yu C
> Cc: linux-pm@...r.kernel.org; x86@...nel.org; Rafael J. Wysocki; Len Brown;
> Peter Zijlstra; H. Peter Anvin; Borislav Petkov; Brian Gerst; Thomas Gleixner;
> Ingo Molnar; Varun Koyyalagunta; linux-kernel@...r.kernel.org
> Subject: Re: [PATCH 1/4][RFC v2] PM / sleep: Avoid accessing frozen_cpus if it
> is NULL
> 
> On Sun 2016-06-26 00:18:30, Chen Yu wrote:
> > frozen_cpus might be NULL if the allocation in previous
> > alloc_frozen_cpus failed, when CONFIG_CPUMASK_OFFSTACK is set.
> >
> > This patch avoid accessing this cpumask if it is NULL.
> >
> > Signed-off-by: Chen Yu <yu.c.chen@...el.com>
> > ---
> >  kernel/cpu.c | 4 ++++
> >  1 file changed, 4 insertions(+)
> >
> > diff --git a/kernel/cpu.c b/kernel/cpu.c index d948e44..d25266e 100644
> > --- a/kernel/cpu.c
> > +++ b/kernel/cpu.c
> > @@ -1021,6 +1021,8 @@ int disable_nonboot_cpus(void)  {
> >  	int cpu, first_cpu, error = 0;
> >
> > +	if (frozen_cpus == NULL)
> > +		return -ENOMEM;
> >  	cpu_maps_update_begin();
> >  	first_cpu = cpumask_first(cpu_online_mask);
> >  	/*
> 
> I'd say that whoever allocates frozen_cpus should just abort the hibernation if
> there's not enough memory for the operation...? This seems like checking for
> the problem too late.
> 
The allocation of frozen_cpus is alloc_frozen_cpus, which is in core_initcall,
and do_initcall during boot up  seems not to care about the return value from 
these functions.  So I think either we add the check in disable_nonboot_cpus, or
we can set noresume = 1 and nohibernate = 1 if alloc_frozen_cpus fails.

thanks,
Yu