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[PATCH v2] perf/aux: Properly launch pending disable flow

Leo Yan posted 1 patch 3 months, 2 weeks ago 
kernel/events/core.c        | 6 +++---
kernel/events/ring_buffer.c | 4 ++--
2 files changed, 5 insertions(+), 5 deletions(-)
[PATCH v2] perf/aux: Properly launch pending disable flow
Posted by Leo Yan 3 months, 2 weeks ago 
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.

Since commit ca6c21327c6a ("perf: Fix missing SIGTRAPs"), the
'pending_disable' flag was changed to a boolean toggles. 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 2b84def990d3 ("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 issue, when an AUX ring buffer overrun is detected, call
perf_event_disable_inatomic() to initiate the pending disable flow.

The comment for setting the flag is outdated; update it to reflect the
boolean values (0 or 1).

Fixes: ca6c21327c6a ("perf: Fix missing SIGTRAPs")
Fixes: 2b84def990d3 ("perf: Split __perf_pending_irq() out of perf_pending_irq()")
Reviewed-by: James Clark <james.clark@linaro.org>
Reviewed-by: Yeoreum Yun <yeoreum.yun@arm.com>
Signed-off-by: Leo Yan <leo.yan@arm.com>
---

Changes from v1:
- Updated the comment for boolean values (0 or 1) (James Clark).

 kernel/events/core.c        | 6 +++---
 kernel/events/ring_buffer.c | 4 ++--
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 1f746469fda5..7281230044d0 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -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()
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index d2aef87c7e9f..aa9a759e824f 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -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);
 	}
 
-- 
2.34.1
[tip: perf/urgent] perf/aux: Fix pending disable flow when the AUX ring buffer overruns
Posted by tip-bot2 for Leo Yan 3 months, 2 weeks ago 
The following commit has been merged into the perf/urgent branch of tip:

Commit-ID:     1476b218327b89bbb64c14619a2d34f0c320f2c3
Gitweb:        https://git.kernel.org/tip/1476b218327b89bbb64c14619a2d34f0c320f2c3
Author:        Leo Yan <leo.yan@arm.com>
AuthorDate:    Wed, 25 Jun 2025 18:07:37 +01:00
Committer:     Ingo Molnar <mingo@kernel.org>
CommitterDate: Thu, 26 Jun 2025 10:50:37 +02:00

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:

  ca6c21327c6a ("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:

  2b84def990d3 ("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: 2b84def990d3 ("perf: Split __perf_pending_irq() out of perf_pending_irq()")
Fixes: ca6c21327c6a ("perf: Fix missing SIGTRAPs")
Signed-off-by: Leo Yan <leo.yan@arm.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Reviewed-by: James Clark <james.clark@linaro.org>
Reviewed-by: Yeoreum 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
---
 kernel/events/core.c        | 6 +++---
 kernel/events/ring_buffer.c | 4 ++--
 2 files changed, 5 insertions(+), 5 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 1f74646..7281230 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -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()
diff --git a/kernel/events/ring_buffer.c b/kernel/events/ring_buffer.c
index d2aef87..aa9a759 100644
--- a/kernel/events/ring_buffer.c
+++ b/kernel/events/ring_buffer.c
@@ -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);
 	}

Patchew 2.1-devel-b67e4c2

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