linux-kernel - Re: [PATCH v4 1/4] cacheinfo: Check for null last-level cache info

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Message-ID: <20240125143533.GA16226@ranerica-svr.sc.intel.com>
Date: Thu, 25 Jan 2024 06:35:33 -0800
From: Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To: Sudeep Holla <sudeep.holla@....com>
Cc: x86@...nel.org, Andreas Herrmann <aherrmann@...e.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Chen Yu <yu.c.chen@...el.com>, Len Brown <len.brown@...el.com>,
	Radu Rendec <rrendec@...hat.com>,
	Pierre Gondois <Pierre.Gondois@....com>, Pu Wen <puwen@...on.cn>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Will Deacon <will@...nel.org>, Zhang Rui <rui.zhang@...el.com>,
	Huang Ying <ying.huang@...el.com>,
	"Ravi V. Shankar" <ravi.v.shankar@...el.com>,
	stable@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v4 1/4] cacheinfo: Check for null last-level cache info

On Thu, Jan 25, 2024 at 11:15:44AM +0000, Sudeep Holla wrote:
> On Tue, Dec 12, 2023 at 02:25:16PM -0800, Ricardo Neri wrote:
> > Before determining the validity of the last-level cache info, ensure that
> > it has been allocated. Simply checking for non-zero cache_leaves() is not
> > sufficient, as some architectures (e.g., Intel processors) have non-zero
> > cache_leaves() before allocation.
> > 
> > Dereferencing NULL cacheinfo can occur in update_per_cpu_data_slice_size().
> > This function iterates over all online CPUs. However, a CPU may have come
> > online recently, but its cacheinfo may not have been allocated yet.
> > 
> > Cc: Andreas Herrmann <aherrmann@...e.com>
> > Cc: Catalin Marinas <catalin.marinas@....com>
> > Cc: Chen Yu <yu.c.chen@...el.com>
> > Cc: Huang Ying <ying.huang@...el.com>
> > Cc: Len Brown <len.brown@...el.com>
> > Cc: Radu Rendec <rrendec@...hat.com>
> > Cc: Pierre Gondois <Pierre.Gondois@....com>
> > Cc: Pu Wen <puwen@...on.cn>
> > Cc: "Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
> > Cc: Sudeep Holla <sudeep.holla@....com>
> 
> If you respin, you can address the below minor nit. I am fine as is as
> well.
> 
> Reviewed-by: Sudeep Holla <sudeep.holla@....com>

Thank you for your review Sudeep!

> 
> [...]
> 
> > diff --git a/drivers/base/cacheinfo.c b/drivers/base/cacheinfo.c
> > index f1e79263fe61..967c5cf3fb1d 100644
> > --- a/drivers/base/cacheinfo.c
> > +++ b/drivers/base/cacheinfo.c
> > @@ -61,6 +61,9 @@ bool last_level_cache_is_valid(unsigned int cpu)
> >  	if (!cache_leaves(cpu))
> >  		return false;
> >  
> > +	if (!per_cpu_cacheinfo(cpu))
> > +		return false;
> > +
> 
> [nit] You can even combine this with above if condition.

Sure, I can take care of this if a new version is needed as per feedback
from the x86 maintainers.