[PATCH] perf: Fix lockdep warning in perf_event_throttle_group

[Jianhui Zhou]

When perf samples a tracepoint like trace_lock_acquire with high
frequency, it can trigger a WARN_ON in perf_event_throttle_group()
due to lockdep assertion failure in for_each_sibling_event().

The issue is that for_each_sibling_event() requires either:
1. Holding ctx->mutex, OR
2. Having IRQs disabled (since ctx->lock is IRQ-safe)

The call trace shows the problematic path:
futex_wake
  lock_acquire
    trace_lock_acquire
      perf_trace_lock_acquire
        perf_tp_event
          perf_swevent_event
            __perf_event_overflow
              __perf_event_account_interrupt
                perf_event_throttle_group
                  for_each_sibling_event [WARN]

In this tracepoint path, IRQs may be enabled and neither ctx->lock
nor ctx->mutex is held.

The fix adds guard(irqsave)() protection around the sibling list
iteration in perf_event_throttle_group().

Reported-by: syzbot+a945e9d15c8a49a7a7f0@xxxxxxxxxxxxxxxxxxxxxxxxx
Closes: https://lore.kernel.org/all/69122cb3.a70a0220.22f260.00ff.GAE@xxxxxxxxxx/T/
Signed-off-by: Jianhui Zhou <jianhuizz@xxxxxx>
---
 kernel/events/core.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 1fd347da9026..253c514e9452 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2700,6 +2700,11 @@ static void perf_event_throttle_group(struct perf_event *event)
 	struct perf_event *sibling, *leader = event->group_leader;
 
 	perf_event_throttle(leader);
+    /*
+     * Disable IRQs to protect sibling iteration; for_each_sibling_event()
+     * needs ctx->mutex or IRQs off.
+     */
+	guard(irqsave)();
 	for_each_sibling_event(sibling, leader)
 		perf_event_throttle(sibling);
 }
-- 
2.43.0