Re: [Intel-gfx] [PATCH 2/2] drm/i915: Only disable PMU on stop if not already closed

["Summers, Stuart" <stuart.summers@intel.com>]

On Thu, 2022-08-04 at 09:46 +0100, Tvrtko Ursulin wrote:
> On 04/08/2022 00:03, Stuart Summers wrote:
> > There can be a race in the PMU process teardown vs the
> > time when the driver is unbound in which the user attempts
> > to stop the PMU process, but the actual data structure
> > in the kernel is no longer available. Avoid this use-after-free
> > by skipping the PMU disable in i915_pmu_event_stop() when
> > the PMU has already been closed/unregistered by the driver.
> > 
> > Fixes: b00bccb3f0bb ("drm/i915/pmu: Handle PCI unbind")
> > Suggested-by: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
> > Signed-off-by: Stuart Summers <stuart.summers@intel.com>
> > ---
> >   drivers/gpu/drm/i915/i915_pmu.c | 8 ++++++++
> >   1 file changed, 8 insertions(+)
> > 
> > diff --git a/drivers/gpu/drm/i915/i915_pmu.c
> > b/drivers/gpu/drm/i915/i915_pmu.c
> > index 958b37123bf12..0d02f338118e4 100644
> > --- a/drivers/gpu/drm/i915/i915_pmu.c
> > +++ b/drivers/gpu/drm/i915/i915_pmu.c
> > @@ -760,9 +760,17 @@ static void i915_pmu_event_start(struct
> > perf_event *event, int flags)
> >   
> >   static void i915_pmu_event_stop(struct perf_event *event, int
> > flags)
> >   {
> > +	struct drm_i915_private *i915 =
> > +		container_of(event->pmu, typeof(*i915), pmu.base);
> > +	struct i915_pmu *pmu = &i915->pmu;
> > +
> > +	if (pmu->closed)
> > +		goto out;
> > +
> >   	if (flags & PERF_EF_UPDATE)
> >   		i915_pmu_event_read(event);
> >   	i915_pmu_disable(event);
> > +out:
> >   	event->hw.state = PERF_HES_STOPPED;
> >   }
> >   
> 
> LGTM, although I am not sure who feels comfortable to r-b since we
> all 
> kind of suggested the same fix. :)
> 
> FWIW:
> 
> Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>

Thanks Tvrtko! I'll track down another reviewer here as well to close
that out before merging.

Thanks,
Stuart

> 
> Regards,
> 
> Tvrtko