linux-kernel - RE: [PATCH v3 2/3] perf: add arm64 smmuv3 pmu driver

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Date:   Wed, 3 Oct 2018 11:28:19 +0000
From:   Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>
To:     Robin Murphy <robin.murphy@....com>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>
CC:     "will.deacon@....com" <will.deacon@....com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "Guohanjun (Hanjun Guo)" <guohanjun@...wei.com>,
        John Garry <john.garry@...wei.com>,
        "pabba@...eaurora.org" <pabba@...eaurora.org>,
        "vkilari@...eaurora.org" <vkilari@...eaurora.org>,
        "rruigrok@...eaurora.org" <rruigrok@...eaurora.org>,
        "linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Linuxarm <linuxarm@...wei.com>,
        "neil.m.leeder@...il.com" <neil.m.leeder@...il.com>
Subject: RE: [PATCH v3 2/3] perf: add arm64 smmuv3 pmu driver



> -----Original Message-----
> From: Robin Murphy [mailto:robin.murphy@....com]
> Sent: 03 October 2018 11:37
> To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi@...wei.com>;
> lorenzo.pieralisi@....com
> Cc: will.deacon@....com; mark.rutland@....com; Guohanjun (Hanjun Guo)
> <guohanjun@...wei.com>; John Garry <john.garry@...wei.com>;
> pabba@...eaurora.org; vkilari@...eaurora.org; rruigrok@...eaurora.org;
> linux-acpi@...r.kernel.org; linux-kernel@...r.kernel.org; linux-arm-
> kernel@...ts.infradead.org; Linuxarm <linuxarm@...wei.com>;
> neil.m.leeder@...il.com
> Subject: Re: [PATCH v3 2/3] perf: add arm64 smmuv3 pmu driver
> 
> On 21/09/18 16:08, Shameer Kolothum wrote:
> [...]
> > +
> > +	err = cpuhp_state_add_instance_nocalls(cpuhp_state_num,
> > +					       &smmu_pmu->node);
> 
> In theory a hotplug event could happen as soon as the instance is
> registered...
> 
> > +	if (err) {
> > +		dev_err(dev, "Error %d registering hotplug, PMU @%pa\n",
> > +			err, &res_0->start);
> > +		return err;
> > +	}
> > +
> > +	/* Pick one CPU to be the preferred one to use */
> > +	smmu_pmu->on_cpu = get_cpu();
> 
> ...so this looks too late, i.e. a race here can result in a bogus call
> to perf_pmu_migrate_context() with an uninitialised pmu.

Thanks Robin. I will reorder them.

Shameer

> Robin. 
> > +	WARN_ON(irq_set_affinity(smmu_pmu->irq, cpumask_of(smmu_pmu-
> >on_cpu)));
> > +
> > +	err = perf_pmu_register(&smmu_pmu->pmu, name, -1);
> > +	if (err) {
> > +		dev_err(dev, "Error %d registering PMU @%pa\n",
> > +			err, &res_0->start);
> > +		goto out_unregister;
> > +	}
> > +
> > +	put_cpu();