linux-kernel - Re: [PATCH v2 08/10] perf/hisi_uncore: Avoid placing cpumask var on stack

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Date: Fri, 5 Apr 2024 10:53:26 +0100
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: Mark Rutland <mark.rutland@....com>
CC: Dawei Li <dawei.li@...ngroup.cn>, <will@...nel.org>,
	<yury.norov@...il.com>, <linux@...musvillemoes.dk>,
	<xueshuai@...ux.alibaba.com>, <renyu.zj@...ux.alibaba.com>,
	<yangyicong@...ilicon.com>, <andersson@...nel.org>,
	<konrad.dybcio@...aro.org>, <linux-arm-kernel@...ts.infradead.org>,
	<linux-kernel@...r.kernel.org>, <linux-arm-msm@...r.kernel.org>
Subject: Re: [PATCH v2 08/10] perf/hisi_uncore: Avoid placing cpumask var on
 stack

On Wed, 3 Apr 2024 15:35:47 +0100
Mark Rutland <mark.rutland@....com> wrote:

> On Wed, Apr 03, 2024 at 08:51:07PM +0800, Dawei Li wrote:
> > For CONFIG_CPUMASK_OFFSTACK=y kernel, explicit allocation of cpumask
> > variable on stack is not recommended since it can cause potential stack
> > overflow.
> > 
> > Instead, kernel code should always use *cpumask_var API(s) to allocate
> > cpumask var in config-neutral way, leaving allocation strategy to
> > CONFIG_CPUMASK_OFFSTACK.
> > 
> > But dynamic allocation in cpuhp's teardown callback is somewhat problematic
> > for if allocation fails(which is unlikely but still possible):
> > - If -ENOMEM is returned to caller, kernel crashes for non-bringup
> >   teardown;
> > - If callback pretends nothing happened and returns 0 to caller, it may
> >   trap system into an in-consisitent/compromised state;
> > 
> > Use newly-introduced cpumask_any_and_but() to address all issues above.
> > It eliminates usage of temporary cpumask var in generic way, no matter how
> > the cpumask var is allocated.
> > 
> > Suggested-by: Mark Rutland <mark.rutland@....com>
> > Signed-off-by: Dawei Li <dawei.li@...ngroup.cn>  
> 
> The logic looks good to me, but I'd like the commit message updated the same as
> per my comment on patch 2.
> 
> With that commit message:
> 
> Reviewed-by: Mark Rutland <mark.rutland@....com>

Acked-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>