[Patch v3 3/7] perf/x86: Check if cpuc->events[*] pointer exists before accessing it

[Dapeng Mi <dapeng1.mi@linux.intel.com>]

When intel_pmu_drain_pebs_icl() is called to drain PEBS records, the
perf_event_overflow() could be called to process the last PEBS record.

While perf_event_overflow() could trigger the interrupt throttle and
stop all events of the group, like what the below call-chain shows.

perf_event_overflow()
  -> __perf_event_overflow()
    ->__perf_event_account_interrupt()
      -> perf_event_throttle_group()
        -> perf_event_throttle()
          -> event->pmu->stop()
            -> x86_pmu_stop()

The side effect of stopping the events is that all corresponding event
pointers in cpuc->events[] array are cleared to NULL.

Assume there are two PEBS events (event a and event b) in a group. When
intel_pmu_drain_pebs_icl() calls perf_event_overflow() to process the
last PEBS record of PEBS event a, interrupt throttle is triggered and
all pointers of event a and event b are cleared to NULL. Then
intel_pmu_drain_pebs_icl() tries to process the last PEBS record of
event b and encounters NULL pointer access.

Since the left PEBS records have been processed when stopping the event,
check and skip to process the last PEBS record if cpuc->events[*] is
NULL.

Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202507042103.a15d2923-lkp@intel.com
Fixes: 9734e25fbf5a ("perf: Fix the throttle logic for a group")
Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Tested-by: kernel test robot <oliver.sang@intel.com>
---
 arch/x86/events/intel/ds.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
index c0b7ac1c7594..dcf29c099ad2 100644
--- a/arch/x86/events/intel/ds.c
+++ b/arch/x86/events/intel/ds.c
@@ -2663,6 +2663,16 @@ static void intel_pmu_drain_pebs_icl(struct pt_regs *iregs, struct perf_sample_d
 			continue;
 
 		event = cpuc->events[bit];
+		/*
+		 * perf_event_overflow() called by below __intel_pmu_pebs_last_event()
+		 * could trigger interrupt throttle and clear all event pointers of the
+		 * group in cpuc->events[] to NULL. So need to re-check if cpuc->events[*]
+		 * is NULL, if so it indicates the event has been throttled (stopped) and
+		 * the corresponding last PEBS records have been processed in stopping
+		 * event, don't need to process it again.
+		 */
+		if (!event)
+			continue;
 
 		__intel_pmu_pebs_last_event(event, iregs, regs, data, last[bit],
 					    counts[bit], setup_pebs_adaptive_sample_data);
-- 
2.34.1