Re: [Patch v2] perf/x86/intel: Prevent drain_pebs() reentry

[Peter Zijlstra]

On Wed, Sep 09, 2026 at 07:09:11PM +0800, Mi, Dapeng wrote:
> Hi Peter,
> 
> Could you please review and queue this patch if it's good enough? This
> version addresses your comments. Thanks.
> 
> 
> On 8/13/2026 2:43 PM, Dapeng Mi wrote:
> > The PEBS buffer is shared by all events on a CPU, so drain_pebs() must
> > not be reentered. If so, one instance may observe stale buffer state and
> > potentially access out-of-bound memory.
> >
> > Most invocations happen in NMI context, which naturally prevents reentry.
> > However, drain_pebs() is also reachable from process context via
> > intel_pmu_drain_pebs_buffer().
> >
> > In those paths, the PMU is often already disabled, but not guaranteed.
> > For example, __intel_pmu_pebs_disable() only disables the target counter,
> > so other active counters can still raise a PMI and interrupt an in-flight
> > drain_pebs(). Here is an example,
> >
> > __perf_addr_filters_adjust()
> >   perf_event_stop()
> >     __perf_event_stop()
> >       x86_pmu_stop() (event->pmu->stop)
> >         intel_pmu_disable_event()
> >           intel_pmu_pebs_disable()
> >             __intel_pmu_pebs_disable()
> >               intel_pmu_drain_large_pebs()
> >                 intel_pmu_drain_pebs_buffer()
> >
> > Introduce __intel_pmu_quiesce() and __intel_pmu_resume() helpers and
> > use them in intel_pmu_drain_large_pebs() to disable the full PMU
> > around the intel_pmu_drain_pebs_buffer() call, preventing reentry.
> >
> > Also add a warning in intel_pmu_drain_pebs_buffer() when the full PMU is
> > not disabled.
> >
> > Signed-off-by: Dapeng Mi <dapeng1.mi@xxxxxxxxxxxxxxx>

Ah yes. Can you get me a Fixes tag to go with this?