Commit 1476b218 authored by Leo Yan's avatar Leo Yan Committed by Ingo Molnar
Browse files

perf/aux: Fix pending disable flow when the AUX ring buffer overruns 



If an AUX event overruns, the event core layer intends to disable the
event by setting the 'pending_disable' flag. Unfortunately, the event
is not actually disabled afterwards.

In commit:

  ca6c2132 ("perf: Fix missing SIGTRAPs")

the 'pending_disable' flag was changed to a boolean. However, the
AUX event code was not updated accordingly. The flag ends up holding a
CPU number. If this number is zero, the flag is taken as false and the
IRQ work is never triggered.

Later, with commit:

  2b84def9 ("perf: Split __perf_pending_irq() out of perf_pending_irq()")

a new IRQ work 'pending_disable_irq' was introduced to handle event
disabling. The AUX event path was not updated to kick off the work queue.

To fix this bug, when an AUX ring buffer overrun is detected, call
perf_event_disable_inatomic() to initiate the pending disable flow.

Also update the outdated comment for setting the flag, to reflect the
boolean values (0 or 1).

Fixes: 2b84def9 ("perf: Split __perf_pending_irq() out of perf_pending_irq()")
Fixes: ca6c2132 ("perf: Fix missing SIGTRAPs")
Signed-off-by: default avatarLeo Yan <leo.yan@arm.com>
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
Reviewed-by: default avatarJames Clark <james.clark@linaro.org>
Reviewed-by: default avatarYeoreum Yun <yeoreum.yun@arm.com>
Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Cc: Ian Rogers <irogers@google.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Liang Kan <kan.liang@linux.intel.com>
Cc: Marco Elver <elver@google.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: linux-perf-users@vger.kernel.org
Link: https://lore.kernel.org/r/20250625170737.2918295-1-leo.yan@arm.com
parent 86731a2a

kernel/events/core.c

+3 −3
Original line number Diff line number Diff line
@@ -7251,15 +7251,15 @@ static void __perf_pending_disable(struct perf_event *event) 
	 *  CPU-A			CPU-B

	 *

	 *  perf_event_disable_inatomic()

	 *    @pending_disable = CPU-A;

	 *    @pending_disable = 1;

	 *    irq_work_queue();

	 *

	 *  sched-out

	 *    @pending_disable = -1;

	 *    @pending_disable = 0;

	 *

	 *				sched-in

	 *				perf_event_disable_inatomic()

	 *				  @pending_disable = CPU-B;

	 *				  @pending_disable = 1;

	 *				  irq_work_queue(); // FAILS

	 *

	 *  irq_work_run()

kernel/events/ring_buffer.c

+2 −2
Original line number Diff line number Diff line
@@ -441,7 +441,7 @@ void *perf_aux_output_begin(struct perf_output_handle *handle, 
		 * store that will be enabled on successful return

		 */

		if (!handle->size) { /* A, matches D */

			event->pending_disable = smp_processor_id();

			perf_event_disable_inatomic(handle->event);

			perf_output_wakeup(handle);

			WRITE_ONCE(rb->aux_nest, 0);

			goto err_put;
@@ -526,7 +526,7 @@ void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size) 


	if (wakeup) {

		if (handle->aux_flags & PERF_AUX_FLAG_TRUNCATED)

			handle->event->pending_disable = smp_processor_id();

			perf_event_disable_inatomic(handle->event);

		perf_output_wakeup(handle);

	}