linux-kernel - [RFC/PATCH for-perf-urgent] perf/core: Change to POLLERR for pinned events with error

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Message-ID: <20250422223318.180343-1-namhyung@kernel.org>
Date: Tue, 22 Apr 2025 15:33:18 -0700
From: Namhyung Kim <namhyung@...nel.org>
To: Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...nel.org>
Cc: Kan Liang <kan.liang@...ux.intel.com>,
	Mark Rutland <mark.rutland@....com>,
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>,
	Arnaldo Carvalho de Melo <acme@...nel.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Gabriel Marin <gmx@...gle.com>
Subject: [RFC/PATCH for-perf-urgent] perf/core: Change to POLLERR for pinned events with error

The commit f4b07fd62d4d11d5 ("perf/core: Use POLLHUP for pinned events
in error") started to emit POLLHUP for pinned events in an error state.

But the POLLHUP is also used to signal events that the attached task is
terminated.  To distinguish pinned per-task events in the error state
it would need to check if the task is live.

If we can change it to POLLERR it should be clear.

Suggested-by: Gabriel Marin <gmx@...gle.com>
Signed-off-by: Namhyung Kim <namhyung@...nel.org>
---
 kernel/events/core.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index e93c195659140d30..95e703891b24f8fc 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -3943,7 +3943,7 @@ static int merge_sched_in(struct perf_event *event, void *data)
 			perf_event_set_state(event, PERF_EVENT_STATE_ERROR);
 
 			if (*perf_event_fasync(event))
-				event->pending_kill = POLL_HUP;
+				event->pending_kill = POLL_ERR;
 
 			perf_event_wakeup(event);
 		} else {
@@ -6075,7 +6075,7 @@ static __poll_t perf_poll(struct file *file, poll_table *wait)
 
 	if (unlikely(READ_ONCE(event->state) == PERF_EVENT_STATE_ERROR &&
 		     event->attr.pinned))
-		return events;
+		return EPOLLERR;
 
 	/*
 	 * Pin the event->rb by taking event->mmap_mutex; otherwise
-- 
2.49.0.805.g082f7c87e0-goog