Re: [Patch v3 8/8] perf/x86/intel: Prevent drain_pebs() reentry

[Peter Zijlstra]

On Fri, Jul 17, 2026 at 04:03:42PM +0800, Dapeng Mi wrote:
> The PEBS buffer is shared by all events on a CPU, so drain_pebs() must
> not run concurrently. If it is reentered, 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().
> 
> Introduce __intel_pmu_quiesce() and __intel_pmu_resume() helpers and
> use them in intel_pmu_drain_pebs_buffer() to disable the full PMU
> around the drain_pebs() call, preventing reentry.
> 

It is not at all clear to me where the exact recursion happens. (The
word you're looking for was recursion, not concurrent).