perf/core: Fix invalid wait context in ctx_sched_in()

Lockdep found a bug in the event scheduling when a pinned event was
failed and wakes up the threads in the ring buffer like below.

It seems it should not grab a wait-queue lock under perf-context lock.
Let's do it with irq_work.

  [   39.913691] =============================
  [   39.914157] [ BUG: Invalid wait context ]
  [   39.914623] 6.15.0-next-20250530-next-2025053 #1 Not tainted
  [   39.915271] -----------------------------
  [   39.915731] repro/837 is trying to lock:
  [   39.916191] ffff88801acfabd8 (&event->waitq){....}-{3:3}, at: __wake_up+0x26/0x60
  [   39.917182] other info that might help us debug this:
  [   39.917761] context-{5:5}
  [   39.918079] 4 locks held by repro/837:
  [   39.918530]  #0: ffffffff8725cd00 (rcu_read_lock){....}-{1:3}, at: __perf_event_task_sched_in+0xd1/0xbc0
  [   39.919612]  #1: ffff88806ca3c6f8 (&cpuctx_lock){....}-{2:2}, at: __perf_event_task_sched_in+0x1a7/0xbc0
  [   39.920748]  #2: ffff88800d91fc18 (&ctx->lock){....}-{2:2}, at: __perf_event_task_sched_in+0x1f9/0xbc0
  [   39.921819]  #3: ffffffff8725cd00 (rcu_read_lock){....}-{1:3}, at: perf_event_wakeup+0x6c/0x470

Fixes: f4b07fd ("perf/core: Use POLLHUP for a pinned event in error")
Closes: https://lore.kernel.org/lkml/aD2w50VDvGIH95Pf@ly-workstation
Reported-by: "Lai, Yi" <yi1.lai@linux.intel.com>
Signed-off-by: Namhyung Kim <namhyung@kernel.org>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Tested-by: "Lai, Yi" <yi1.lai@linux.intel.com>
Link: https://patch.msgid.link/20250603045105.1731451-1-namhyung@kernel.org

Author: namhyung

kernel/events/core.c

@@ -4138,7 +4138,8 @@ static int merge_sched_in(struct perf_event *event, void *data)
 			if (*perf_event_fasync(event))
 				event->pending_kill = POLL_ERR;
 
-			perf_event_wakeup(event);
+			event->pending_wakeup = 1;
+			irq_work_queue(&event->pending_irq);
 		} else {
 			struct perf_cpu_pmu_context *cpc = this_cpc(event->pmu_ctx->pmu);