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Subject[RFC] perf/x86/intel: Account interrupts for PEBS errors
hi,
I'm hitting soft lockup generated by fuzzer, where the
perf hangs in remote_install path like:

NMI watchdog: BUG: soft lockup - CPU#22 stuck for 22s! [perf_fuzzer:5816]

task: ffff880273148000 task.stack: ffffc90002d58000
RIP: 0010:[<ffffffff81159232>] [<ffffffff81159232>] smp_call_function_single+0xe2/0x140
RSP: 0018:ffffc90002d5bd60 EFLAGS: 00000202
...
Call Trace:
[<ffffffff81114ce5>] ? trace_hardirqs_on_caller+0xf5/0x1b0
[<ffffffff811e20e0>] ? perf_cgroup_attach+0x70/0x70
[<ffffffff811e1049>] perf_install_in_context+0x199/0x1b0
[<ffffffff811e74e0>] ? ctx_resched+0x90/0x90
[<ffffffff811ed9d1>] SYSC_perf_event_open+0x641/0xf90
[<ffffffff811f1069>] SyS_perf_event_open+0x9/0x10
[<ffffffff81003edc>] do_syscall_64+0x6c/0x1f0
[<ffffffff818defc9>] entry_SYSCALL64_slow_path+0x25/0x25


I found out that I could reproduce this with following
2 perf commands running simultaneously:

taskset -c 1 ./perf record -c 4 -e branches:pp -j any -C 10

this forces cpu 10 to endless loop causing the soft lockup

AFAICS the reason for this is that intel_pmu_drain_pebs_nhm does
not account event->hw.interrupt for error PEBS interrupts, so in
case you're getting ONLY errors you dont have a way to stop event
when it's over the max_samples_per_tick limit

I added extra accounting for error PEBS and it seems to work now,
fuzzer is running for several hours now ;-)

also I could not reproduce with any other event, just branches plus
the additional branch stack sample type

I also fail to reproduce on other than snb_x (model 45) server

thoughts?

thanks,
jirka


---
diff --git a/arch/x86/events/intel/ds.c b/arch/x86/events/intel/ds.c
index be202390bbd3..f2010dbe75d6 100644
--- a/arch/x86/events/intel/ds.c
+++ b/arch/x86/events/intel/ds.c
@@ -1389,9 +1389,13 @@ static void intel_pmu_drain_pebs_nhm(struct pt_regs *iregs)
continue;

/* log dropped samples number */
- if (error[bit])
+ if (error[bit]) {
perf_log_lost_samples(event, error[bit]);

+ if (perf_event_account_interrupt(event, 1))
+ x86_pmu_stop(event, 0);
+ }
+
if (counts[bit]) {
__intel_pmu_pebs_event(event, iregs, base,
top, bit, counts[bit]);
diff --git a/include/linux/perf_event.h b/include/linux/perf_event.h
index 4741ecdb9817..7225396228ce 100644
--- a/include/linux/perf_event.h
+++ b/include/linux/perf_event.h
@@ -1259,6 +1259,7 @@ extern void perf_event_disable(struct perf_event *event);
extern void perf_event_disable_local(struct perf_event *event);
extern void perf_event_disable_inatomic(struct perf_event *event);
extern void perf_event_task_tick(void);
+extern int perf_event_account_interrupt(struct perf_event *event, int throttle);
#else /* !CONFIG_PERF_EVENTS: */
static inline void *
perf_aux_output_begin(struct perf_output_handle *handle,
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 02c8421f8c01..93b46cc2c977 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7034,25 +7034,11 @@ static void perf_log_itrace_start(struct perf_event *event)
perf_output_end(&handle);
}

-/*
- * Generic event overflow handling, sampling.
- */
-
-static int __perf_event_overflow(struct perf_event *event,
- int throttle, struct perf_sample_data *data,
- struct pt_regs *regs)
+int perf_event_account_interrupt(struct perf_event *event, int throttle)
{
- int events = atomic_read(&event->event_limit);
struct hw_perf_event *hwc = &event->hw;
- u64 seq;
int ret = 0;
-
- /*
- * Non-sampling counters might still use the PMI to fold short
- * hardware counters, ignore those.
- */
- if (unlikely(!is_sampling_event(event)))
- return 0;
+ u64 seq;

seq = __this_cpu_read(perf_throttled_seq);
if (seq != hwc->interrupts_seq) {
@@ -7070,6 +7056,30 @@ static int __perf_event_overflow(struct perf_event *event,
}
}

+ return ret;
+}
+
+/*
+ * Generic event overflow handling, sampling.
+ */
+
+static int __perf_event_overflow(struct perf_event *event,
+ int throttle, struct perf_sample_data *data,
+ struct pt_regs *regs)
+{
+ int events = atomic_read(&event->event_limit);
+ struct hw_perf_event *hwc = &event->hw;
+ int ret = 0;
+
+ /*
+ * Non-sampling counters might still use the PMI to fold short
+ * hardware counters, ignore those.
+ */
+ if (unlikely(!is_sampling_event(event)))
+ return 0;
+
+ ret = perf_event_account_interrupt(event, throttle);
+
if (event->attr.freq) {
u64 now = perf_clock();
s64 delta = now - hwc->freq_time_stamp;
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