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@linux.ibm.com> Tested-by: Thomas Richter <tmricht@linux.ibm.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Acked-by: Mark Rutland <mark.rutland@arm.com> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: Hendrik Brueckner <brueckner@linux.ibm.com> Cc: Jiri Olsa <jolsa@redhat.com> Cc: Kees Cook <keescook@chromium.org> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Ingo Molnar <mingo@kernel.org>
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@ -2009,8 +2009,8 @@ event_sched_out(struct perf_event *event,
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event->pmu->del(event, 0);
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event->oncpu = -1;
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if (event->pending_disable) {
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event->pending_disable = 0;
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if (READ_ONCE(event->pending_disable) >= 0) {
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WRITE_ONCE(event->pending_disable, -1);
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state = PERF_EVENT_STATE_OFF;
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}
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perf_event_set_state(event, state);
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@ -2198,7 +2198,8 @@ EXPORT_SYMBOL_GPL(perf_event_disable);
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void perf_event_disable_inatomic(struct perf_event *event)
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{
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event->pending_disable = 1;
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WRITE_ONCE(event->pending_disable, smp_processor_id());
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/* can fail, see perf_pending_event_disable() */
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irq_work_queue(&event->pending);
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}
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@ -5810,10 +5811,45 @@ void perf_event_wakeup(struct perf_event *event)
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}
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}
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static void perf_pending_event_disable(struct perf_event *event)
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{
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int cpu = READ_ONCE(event->pending_disable);
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if (cpu < 0)
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return;
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if (cpu == smp_processor_id()) {
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WRITE_ONCE(event->pending_disable, -1);
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perf_event_disable_local(event);
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return;
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}
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/*
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* CPU-A CPU-B
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*
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* perf_event_disable_inatomic()
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* @pending_disable = CPU-A;
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* irq_work_queue();
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*
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* sched-out
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* @pending_disable = -1;
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*
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* sched-in
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* perf_event_disable_inatomic()
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* @pending_disable = CPU-B;
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* irq_work_queue(); // FAILS
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*
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* irq_work_run()
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* perf_pending_event()
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*
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* But the event runs on CPU-B and wants disabling there.
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*/
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irq_work_queue_on(&event->pending, cpu);
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}
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static void perf_pending_event(struct irq_work *entry)
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{
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struct perf_event *event = container_of(entry,
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struct perf_event, pending);
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struct perf_event *event = container_of(entry, struct perf_event, pending);
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int rctx;
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rctx = perf_swevent_get_recursion_context();
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@ -5822,10 +5858,7 @@ static void perf_pending_event(struct irq_work *entry)
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* and we won't recurse 'further'.
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*/
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if (event->pending_disable) {
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event->pending_disable = 0;
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perf_event_disable_local(event);
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}
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perf_pending_event_disable(event);
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if (event->pending_wakeup) {
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event->pending_wakeup = 0;
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@ -10236,6 +10269,7 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu,
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init_waitqueue_head(&event->waitq);
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event->pending_disable = -1;
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init_irq_work(&event->pending, perf_pending_event);
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mutex_init(&event->mmap_mutex);
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@ -392,7 +392,7 @@ void *perf_aux_output_begin(struct perf_output_handle *handle,
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* store that will be enabled on successful return
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*/
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if (!handle->size) { /* A, matches D */
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event->pending_disable = 1;
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event->pending_disable = smp_processor_id();
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perf_output_wakeup(handle);
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local_set(&rb->aux_nest, 0);
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goto err_put;
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@ -480,7 +480,7 @@ void perf_aux_output_end(struct perf_output_handle *handle, unsigned long size)
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if (wakeup) {
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if (handle->aux_flags & PERF_AUX_FLAG_TRUNCATED)
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handle->event->pending_disable = 1;
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handle->event->pending_disable = smp_processor_id();
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perf_output_wakeup(handle);
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}
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