[PATCH] s390/pai: Handle multiple PMU stop callback invocations

Handle the following scenario:
The kernel protects itself against a very high sampling load and
throttles the sampling using:

  perf_event_throttle() --> PMU->stop()

Shortly later the scheduler may terminate the task and removes it from the
CPU. It again calls

  PMU->stop()

which results in two invocations of PMU->stop() called back to back.
Protect against this and check the PERF_HES_STOPPED bit on function
entry.  If it is already set return.
Clear bit PERF_HES_STOPPED in PMU->start().

Cc: [email protected] # v6.19+
Fixes: 9f66572f2889 ("s390/pai_crypto: Enable per-task and system-wide sampling event")
Fixes: 582cc1b28e8c ("s390/pai_ext: Enable per-task and system-wide sampling event")

Signed-off-by: Thomas Richter <[email protected]>
Reviewed-by: Sumanth Korikkar <[email protected]>
---
 arch/s390/kernel/perf_pai.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/arch/s390/kernel/perf_pai.c b/arch/s390/kernel/perf_pai.c
index 1e5a1f1cc68a..f6790f658f21 100644
--- a/arch/s390/kernel/perf_pai.c
+++ b/arch/s390/kernel/perf_pai.c
@@ -484,6 +484,7 @@ static void pai_start(struct perf_event *event, int flags,
 			cpump->event = event;
 		}
 	}
+	event->hw.state &= ~PERF_HES_STOPPED;
 }
 
 static void paicrypt_start(struct perf_event *event, int flags)
@@ -530,6 +531,13 @@ static void pai_stop(struct perf_event *event, int flags)
 	struct pai_mapptr *mp = this_cpu_ptr(pai_root[idx].mapptr);
 	struct pai_map *cpump = mp->mapptr;
 
+	/* Cope with multiple invocations:
+	 *   1. perf_event_throttle() --> PMU->stop()
+	 *   2. task schedules out --> PMU->stop()
+	 * Check for event already stopped.
+	 */
+	if (event->hw.state & PERF_HES_STOPPED)
+		return;
 	if (!event->attr.sample_period) {	/* Counting */
 		pai_pmu[idx].pmu->read(event);
 	} else {				/* Sampling */
-- 
2.55.0