[PATCH v4] 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().

Prohibit ioctl(fd, PERF_EVENT_IOC_PERIOD, ...) call for this event.
It sets perf_event::event_limit to a positive value and causes
perf_event_overflow() to invoke pai_stop() call back function when
perf_event::event_limit hits zero. This is not supported because the
sample events CRYPTO_ALL and NNPA_ALL are only taken at schedule out
of a task.

Use list_for_each_entry_safe() for safe iteration over syswide_list
in pai_have_samples().

 #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]>
Suggested-by: Heiko Carstens <[email protected]>
---
 arch/s390/kernel/perf_pai.c | 25 +++++++++++++++++++++++--
 1 file changed, 23 insertions(+), 2 deletions(-)

diff --git a/arch/s390/kernel/perf_pai.c b/arch/s390/kernel/perf_pai.c
index cdb8006220ca..05f74d74fad1 100644
--- a/arch/s390/kernel/perf_pai.c
+++ b/arch/s390/kernel/perf_pai.c
@@ -464,6 +464,7 @@ 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)
@@ -510,6 +511,13 @@ 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 */
@@ -672,9 +680,9 @@ static void pai_have_samples(int idx)
 {
 	struct pai_mapptr *mp = this_cpu_ptr(pai_root[idx].mapptr);
 	struct pai_map *cpump = mp->mapptr;
-	struct perf_event *event;
+	struct perf_event *event, *e2;
 
-	list_for_each_entry(event, &cpump->syswide_list, hw.tp_list)
+	list_for_each_entry_safe(event, e2, &cpump->syswide_list, hw.tp_list)
 		pai_have_sample(event, cpump);
 }
 
@@ -691,6 +699,17 @@ static void paicrypt_sched_task(struct perf_event_pmu_context *pmu_ctx,
 		pai_have_samples(PAI_PMU_CRYPTO);
 }
 
+/* Prevent ioctl(fd, PERF_EVENT_IOC_PERIOD, ...) call.
+ * It sets perf_event::event_limit to a positive value and causes
+ * perf_event_overflow() to invoke pai_stop() call back function when
+ * perf_event::event_limit hits zero. This is not supported because the
+ * sample events CRYPTO_ALL and NNPA_ALL are always taken at schedule out
+ * of a task.
+ */
+static int pai_check_period(struct perf_event *event, u64 value)
+{
+	return -EINVAL;
+}
 /* ============================= paiext ====================================*/
 
 static void paiext_event_destroy(struct perf_event *event)
@@ -804,6 +823,7 @@ static struct pmu paicrypt = {
 	.stop	      = paicrypt_stop,
 	.read	      = paicrypt_read,
 	.sched_task   = paicrypt_sched_task,
+	.check_period = pai_check_period,
 	.attr_groups  = paicrypt_attr_groups
 };
 
@@ -1015,6 +1035,7 @@ static struct pmu paiext = {
 	.stop	      = paiext_stop,
 	.read	      = paiext_read,
 	.sched_task   = paiext_sched_task,
+	.check_period = pai_check_period,
 	.attr_groups  = paiext_attr_groups,
 };
 
-- 
2.55.0