Commit-ID: 86071b11317550d994b55ce5e31aa06bcad783b5
Gitweb: https://git.kernel.org/tip/86071b11317550d994b55ce5e31aa06bcad783b5
Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
AuthorDate: Thu, 4 Apr 2019 15:03:00 +0200
Committer: Ingo Molnar <mingo@xxxxxxxxxx>
CommitDate: Wed, 10 Apr 2019 13:47:09 +0200
perf/core: Fix perf_event_disable_inatomic() race
Thomas-Mich Richter reported he triggered a WARN()ing from event_function_local()
on his s390. The problem boils down to:
CPU-A CPU-B
perf_event_overflow()
perf_event_disable_inatomic()
@pending_disable = 1
irq_work_queue();
sched-out
event_sched_out()
@pending_disable = 0
sched-in
perf_event_overflow()
perf_event_disable_inatomic()
@pending_disable = 1;
irq_work_queue(); // FAILS
irq_work_run()
perf_pending_event()
if (@pending_disable)
perf_event_disable_local(); // WHOOPS
The problem exists in generic, but s390 is particularly sensitive
because it doesn't implement arch_irq_work_raise(), nor does it call
irq_work_run() from it's PMU interrupt handler (nor would that be
sufficient in this case, because s390 also generates
perf_event_overflow() from pmu::stop). Add to that the fact that s390
is a virtual architecture and (virtual) CPU-A can stall long enough
for the above race to happen, even if it would self-IPI.
Adding a irq_work_sync() to event_sched_in() would work for all hardare
PMUs that properly use irq_work_run() but fails for software PMUs.
Instead encode the CPU number in @pending_disable, such that we can
tell which CPU requested the disable. This then allows us to detect
the above scenario and even redirect the IPI to make up for the failed
queue.
Reported-by: Thomas-Mich Richter <tmricht@xxxxxxxxxxxxx>
Tested-by: Thomas Richter <tmricht@xxxxxxxxxxxxx>
Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
Acked-by: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Alexander Shishkin <alexander.shishkin@xxxxxxxxxxxxxxx>
Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Cc: Hendrik Brueckner <brueckner@xxxxxxxxxxxxx>
Cc: Jiri Olsa <jolsa@xxxxxxxxxx>
Cc: Kees Cook <keescook@xxxxxxxxxxxx>
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Martin Schwidefsky <schwidefsky@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxxxxx>
---
kernel/events/core.c | 52 +++++++++++++++++++++++++++++++++++++++++++---------
1 file changed, 43 insertions(+), 9 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 72d06e302e99..534e01e7bc36 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -2009,8 +2009,8 @@ event_sched_out(struct perf_event *event,
event->pmu->del(event, 0);
event->oncpu = -1;
- if (event->pending_disable) {
- event->pending_disable = 0;
+ if (READ_ONCE(event->pending_disable) >= 0) {
+ WRITE_ONCE(event->pending_disable, -1);
state = PERF_EVENT_STATE_OFF;
}
perf_event_set_state(event, state);
@@ -2198,7 +2198,8 @@ EXPORT_SYMBOL_GPL(perf_event_disable);
void perf_event_disable_inatomic(struct perf_event *event)
{
- event->pending_disable = 1;
+ WRITE_ONCE(event->pending_disable, smp_processor_id());
+ /* can fail, see perf_pending_event_disable() */
irq_work_queue(&event->pending);
}
@@ -5810,10 +5811,45 @@ void perf_event_wakeup(struct perf_event *event)
}
}
+static void perf_pending_event_disable(struct perf_event *event)
+{
+ int cpu = READ_ONCE(event->pending_disable);
+
+ if (cpu < 0)
+ return;
+
+ if (cpu == smp_processor_id()) {
+ WRITE_ONCE(event->pending_disable, -1);
+ perf_event_disable_local(event);
+ return;
+ }
+
+ /*
+ * CPU-A CPU-B
+ *
+ * perf_event_disable_inatomic()
+ * @pending_disable = CPU-A;
+ * irq_work_queue();
+ *
+ * sched-out
+ * @pending_disable = -1;
+ *
+ * sched-in
+ * perf_event_disable_inatomic()
+ * @pending_disable = CPU-B;
+ * irq_work_queue(); // FAILS
+ *
+ * irq_work_run()
+ * perf_pending_event()
+ *
+ * But the event runs on CPU-B and wants disabling there.
+ */
+ irq_work_queue_on(&event->pending, cpu);
+}
+
static void perf_pending_event(struct irq_work *entry)
{
- struct perf_event *event = container_of(entry,
- struct perf_event, pending);
+ struct perf_event *event = container_of(entry, struct perf_event, pending);
int rctx;
rctx = perf_swevent_get_recursion_context();
@@ -5822,10 +5858,7 @@ static void perf_pending_event(struct irq_work *entry)
* and we won't recurse 'further'.
*/
- if (event->pending_disable) {
- event->pending_disable = 0;
- perf_event_disable_local(event);
- }
+ perf_pending_event_disable(event);
if (event->pending_wakeup) {
event->pending_wakeup = 0;
@@ -10236,6 +10269,7 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
init_waitqueue_head(&event->waitq);
+ event->pending_disable = -1;
init_irq_work(&event->pending, perf_pending_event);
mutex_init(&event->mmap_mutex);
|