linux-kernel - Re: [PATCH] drivers/perf: xgene_pmu: Fix uninitialized resource struct

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Date:   Tue, 08 Sep 2020 14:37:22 -0400
From:   Mark Salter <msalter@...hat.com>
To:     Will Deacon <will@...nel.org>
Cc:     Mark Rutland <mark.rutland@....com>,
        Khuong Dinh <khuong@...amperecomputing.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drivers/perf: xgene_pmu: Fix uninitialized resource
 struct

On Mon, 2020-09-07 at 14:50 +0100, Will Deacon wrote:
> On Wed, Sep 02, 2020 at 02:27:29PM -0400, Mark Salter wrote:
> > diff --git a/drivers/perf/xgene_pmu.c b/drivers/perf/xgene_pmu.c
> > index edac28cd25dd..fdbbd0804b92 100644
> > --- a/drivers/perf/xgene_pmu.c
> > +++ b/drivers/perf/xgene_pmu.c
> > @@ -1483,6 +1483,7 @@ xgene_pmu_dev_ctx *acpi_get_pmu_hw_inf(struct xgene_pmu *xgene_pmu,
> >  		return NULL;
> >  
> >  	INIT_LIST_HEAD(&resource_list);
> > +	memset(&res, 0, sizeof(res));
> >  	rc = acpi_dev_get_resources(adev, &resource_list,
> >  				    acpi_pmu_dev_add_resource, &res);
> >  	acpi_dev_free_resource_list(&resource_list);
> 
> Hmm, to be honest, I'm not sure we should be calling devm_ioremap_resource()
> at all here. The resource is clearly bogus, even with this change: the name
> and the resource hierarchy pointers will all be NULL. I think it would be
> better to follow the TX2 PMU driver (drivers/perf/thunderx2_pmu.c) which
> appears to assign the resource directly in tx2_uncore_pmu_init_dev().
> 
> Is there a reason we can't do that?
> 
> Will
> 

There's no difference between xgene and tx2 wrt resouce name/hierarchy.
They both call devm_ioresource_remap() which ends up setting the name
and hierarchy. The difference is that xgene calls acpi_dev_resource_memory()
directly from the acpi_dev_get_resources() callback. TX2 doesn't use such a
callback and in that case, acpi_dev_resource_memory() gets called with a
zeroed struct.

That said, changing xgene to avoid the callback like TX2 does would fix the
problem as well. If you'd rather go that route, I can send a patch for it.

Mark