From: Anand K Mistry amistry@google.com
[ Upstream commit 02d029a41dc986e2d5a77ecca45803857b346829 ]
perf_init_event tries multiple init callbacks and does not reset the event state between tries. When x86_pmu_event_init runs, it unconditionally sets the destroy callback to hw_perf_event_destroy. On the next init attempt after x86_pmu_event_init, in perf_try_init_event, if the pmu's capabilities includes PERF_PMU_CAP_NO_EXCLUDE, the destroy callback will be run. However, if the next init didn't set the destroy callback, hw_perf_event_destroy will be run (since the callback wasn't reset).
Looking at other pmu init functions, the common pattern is to only set the destroy callback on a successful init. Resetting the callback on failure tries to replicate that pattern.
This was discovered after commit f11dd0d80555 ("perf/x86/amd/ibs: Extend PERF_PMU_CAP_NO_EXCLUDE to IBS Op") when the second (and only second) run of the perf tool after a reboot results in 0 samples being generated. The extra run of hw_perf_event_destroy results in active_events having an extra decrement on each perf run. The second run has active_events == 0 and every subsequent run has active_events < 0. When active_events == 0, the NMI handler will early-out and not record any samples.
Signed-off-by: Anand K Mistry amistry@google.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Link: https://lkml.kernel.org/r/20210929170405.1.I078b98ee7727f9ae9d6df8262bad7e32... Signed-off-by: Sasha Levin sashal@kernel.org --- arch/x86/events/core.c | 1 + 1 file changed, 1 insertion(+)
diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index 429389489eed..f612eb1cc818 100644 --- a/arch/x86/events/core.c +++ b/arch/x86/events/core.c @@ -2096,6 +2096,7 @@ static int x86_pmu_event_init(struct perf_event *event) if (err) { if (event->destroy) event->destroy(event); + event->destroy = NULL; }
if (READ_ONCE(x86_pmu.attr_rdpmc) &&