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Date:   Thu, 18 May 2023 10:34:14 +0100
From:   Sudeep Holla <sudeep.holla@arm.com>
To:     Ricardo Neri <ricardo.neri-calderon@linux.intel.com>
Cc:     Radu Rendec <rrendec@redhat.com>, linux-kernel@vger.kernel.org,
        Catalin Marinas <catalin.marinas@arm.com>,
        Sudeep Holla <sudeep.holla@arm.com>,
        Will Deacon <will@kernel.org>,
        Pierre Gondois <Pierre.Gondois@arm.com>,
        linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v4 1/3] cacheinfo: Add arch specific early level
 initializer
Message-ID: <20230518093414.qhwyogcig4wv3r5s@bogus>
References: <20230412185759.755408-1-rrendec@redhat.com>
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 <20230510191207.GA18514@ranerica-svr.sc.intel.com>
 <20230515093608.etfprpqn3lmgybe6@bogus>
 <20230518012703.GA19967@ranerica-svr.sc.intel.com>
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On Wed, May 17, 2023 at 06:27:03PM -0700, Ricardo Neri wrote:
> 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.

Thanks, I thought it is different issue and good that you were able to test
them as well. Please post a proper patch for the NULL ptr dereference you
are hitting on x86.

-- 
Regards,
Sudeep