From 75f80859b130a1cc84e59e71295ce2dd51fe1c81 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Wed, 15 Jul 2015 14:35:46 +0200 Subject: [PATCH] perf/x86/intel/pebs: Robustify PEBS buffer drain Vince Weaver and Stephane Eranian reported warnings in the PEBS code when running the perf fuzzer. Stephane wrote: > I can reproduce the problem on my HSW running the fuzzer. > > I can see why this could be happening if you are mixing PEBS and non PEBS events > in the bottom 4 counters. I suspect: > for (bit = 0; bit < x86_pmu.max_pebs_events; bit++) { > if ((counts[bit] == 0) && (error[bit] == 0)) > continue; > > This test is not correct when you have non-PEBS events mixed with > PEBS events and they overflow at the same time. They will have > counts[i] != 0 but error[i] == 0, and thus you fall thru the loop > and hit the assert. Or it is something along those lines. The only way I can make this work is if ->status only has !PEBS events set, because if it has both set we'll take that slow path which masks out the !PEBS bits. After masking there are 3 options: - there is one bit set, and its @bit, we increment counts[bit]. - there are multiple bits set, we increment error[] for each set bit, we do not increment counts[]. - there are no bits set, we do nothing. The intent was to never increment counts[] for !PEBS events. Now if we start out with only a single !PEBS event set, we'll pass the test and increment counts[] for a !PEBS and hit the warn. Reported-by: Vince Weaver Reported-by: Stephane Eranian Signed-off-by: Peter Zijlstra (Intel) Cc: Arnaldo Carvalho de Melo Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: kan.liang@intel.com Signed-off-by: Ingo Molnar --- arch/x86/kernel/cpu/perf_event_intel_ds.c | 34 +++++++++++------------ 1 file changed, 17 insertions(+), 17 deletions(-) diff --git a/arch/x86/kernel/cpu/perf_event_intel_ds.c b/arch/x86/kernel/cpu/perf_event_intel_ds.c index 8e564f817a7f..84f236ab96b0 100644 --- a/arch/x86/kernel/cpu/perf_event_intel_ds.c +++ b/arch/x86/kernel/cpu/perf_event_intel_ds.c @@ -1188,6 +1188,7 @@ static void intel_pmu_drain_pebs_nhm(struct pt_regs *iregs) for (at = base; at < top; at += x86_pmu.pebs_record_size) { struct pebs_record_nhm *p = at; + u64 pebs_status; /* PEBS v3 has accurate status bits */ if (x86_pmu.intel_cap.pebs_format >= 3) { @@ -1198,12 +1199,17 @@ static void intel_pmu_drain_pebs_nhm(struct pt_regs *iregs) continue; } - bit = find_first_bit((unsigned long *)&p->status, + pebs_status = p->status & cpuc->pebs_enabled; + pebs_status &= (1ULL << x86_pmu.max_pebs_events) - 1; + + bit = find_first_bit((unsigned long *)&pebs_status, x86_pmu.max_pebs_events); - if (bit >= x86_pmu.max_pebs_events) - continue; - if (!test_bit(bit, cpuc->active_mask)) + if (WARN(bit >= x86_pmu.max_pebs_events, + "PEBS record without PEBS event! status=%Lx pebs_enabled=%Lx active_mask=%Lx", + (unsigned long long)p->status, (unsigned long long)cpuc->pebs_enabled, + *(unsigned long long *)cpuc->active_mask)) continue; + /* * The PEBS hardware does not deal well with the situation * when events happen near to each other and multiple bits @@ -1218,27 +1224,21 @@ static void intel_pmu_drain_pebs_nhm(struct pt_regs *iregs) * one, and it's not possible to reconstruct all events * that caused the PEBS record. It's called collision. * If collision happened, the record will be dropped. - * */ - if (p->status != (1 << bit)) { - u64 pebs_status; - - /* slow path */ - pebs_status = p->status & cpuc->pebs_enabled; - pebs_status &= (1ULL << MAX_PEBS_EVENTS) - 1; - if (pebs_status != (1 << bit)) { - for_each_set_bit(i, (unsigned long *)&pebs_status, - MAX_PEBS_EVENTS) - error[i]++; - continue; - } + if (p->status != (1ULL << bit)) { + for_each_set_bit(i, (unsigned long *)&pebs_status, + x86_pmu.max_pebs_events) + error[i]++; + continue; } + counts[bit]++; } for (bit = 0; bit < x86_pmu.max_pebs_events; bit++) { if ((counts[bit] == 0) && (error[bit] == 0)) continue; + event = cpuc->events[bit]; WARN_ON_ONCE(!event); WARN_ON_ONCE(!event->attr.precise_ip); -- 2.34.1