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

> 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()
> [ ... ]
> 
> Also add a warning in intel_pmu_drain_pebs_buffer() when the full PMU is
> not disabled.
> 
> Signed-off-by: Dapeng Mi <[email protected]>

Sashiko has reviewed this patch and found no issues. It looks great!

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