linux-kernel - Re: [PATCH v4 1/3] cacheinfo: Add arch specific early level initializer

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Message-ID: <20230518012703.GA19967@ranerica-svr.sc.intel.com>
Date:   Wed, 17 May 2023 18:27:03 -0700
From:   Ricardo Neri <ricardo.neri-calderon@...ux.intel.com>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     Radu Rendec <rrendec@...hat.com>, linux-kernel@...r.kernel.org,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        Pierre Gondois <Pierre.Gondois@....com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v4 1/3] cacheinfo: Add arch specific early level
 initializer

On Mon, May 15, 2023 at 10:36:08AM +0100, Sudeep Holla wrote:
> On Wed, May 10, 2023 at 12:12:07PM -0700, Ricardo Neri wrote:
> > Hi,
> > 
> > I had posted a patchset[1] for x86 that initializes
> > ci_cacheinfo(cpu)->num_leaves during SMP boot.
> >
> 
> It is entirely clear to me if this is just a clean up or a fix to some
> issue you faced ? Just wanted to let you know Prateek from AMD has couple
> of fixes [2]

My first patch is a bug fix. The second patch is clean up that results
from fixing the bug in patch 1.

> 
> > This means that early_leaves and a late cache_leaves() are equal but
> > per_cpu_cacheinfo(cpu) is never allocated. Currently, x86 does not use
> > fetch_cache_info().
> > 
> > I think that we should check here that per_cpu_cacheinfo() has been allocated to
> > take care of the case in which early and late cache leaves remain the same:
> > 
> > -       if (cache_leaves(cpu) <= early_leaves)
> > +       if (cache_leaves(cpu) <= early_leaves && per_cpu_cacheinfo(cpu))
> > 
> > Otherwise, in v6.4-rc1 + [1] I observe a NULL pointer dereference from
> > last_level_cache_is_valid().
> >
> 
> I think this is different issue as Prateek was just observing wrong info
> after cpuhotplug operations. But the patches manage the cpumap_populated
> state better with the patches. Can you please look at that as weel ?

I verified that the patches from Prateek fix a different issue. I was able
to reproduce his issue. His patches fixes it.

I still see my issue after applying Prateek's patches.
> 
> -- 
> Regards,
> Sudeep
> 
> [2] https://lore.kernel.org/all/20230508084115.1157-1-kprateek.nayak@amd.com

Thank you for the suggestion!

BR,
Ricardo