Subject: [PATCH 1/4] perf: Move irq_work_queue() where the event is prepared.
From: Sebastian Andrzej Siewior <[email-masked]>
Date: Tue, 12 Mar 2024 19:01:49 +0100

Only if perf_event::pending_sigtrap is zero, the irq_work accounted by
increminging perf_event::nr_pending. The member perf_event::pending_addr
might be overwritten by a subsequent event if the signal was not yet
delivered and is expected. The irq_work will not be enqeueued again
because it has a check to be only enqueued once.

Move irq_work_queue() to where the counter is incremented and
perf_event::pending_sigtrap is set to make it more obvious that the
irq_work is scheduled once.

Tested-by: Marco Elver <[email-masked]>
Tested-by: Arnaldo Carvalho de Melo <[email-masked]>
Reported-by: Arnaldo Carvalho de Melo <[email-masked]>
Link: https://lore.kernel.org/r/[email-masked]
Signed-off-by: Sebastian Andrzej Siewior <[email-masked]>
---
 kernel/events/core.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Index: linux-6.8.2-rt10/kernel/events/core.c
===================================================================
--- linux-6.8.2-rt10.orig/kernel/events/core.c
+++ linux-6.8.2-rt10/kernel/events/core.c
@@ -9595,6 +9595,7 @@ static int __perf_event_overflow(struct
 		if (!event->pending_sigtrap) {
 			event->pending_sigtrap = pending_id;
 			local_inc(&event->ctx->nr_pending);
+			irq_work_queue(&event->pending_irq);
 		} else if (event->attr.exclude_kernel && valid_sample) {
 			/*
 			 * Should not be able to return to user space without
@@ -9614,7 +9615,6 @@ static int __perf_event_overflow(struct
 		event->pending_addr = 0;
 		if (valid_sample && (data->sample_flags & PERF_SAMPLE_ADDR))
 			event->pending_addr = data->addr;
-		irq_work_queue(&event->pending_irq);
 	}
 
 	READ_ONCE(event->overflow_handler)(event, data, regs);