From ba5213ae6b88fb170c4771fef6553f759c7d8cdd Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Tue, 30 May 2017 11:45:12 +0200 Subject: [PATCH] perf/core: Correct event creation with PERF_FORMAT_GROUP Andi was asking about PERF_FORMAT_GROUP vs inherited events, which led to the discovery of a bug from commit: 3dab77fb1bf8 ("perf: Rework/fix the whole read vs group stuff") - PERF_SAMPLE_GROUP = 1U << 4, + PERF_SAMPLE_READ = 1U << 4, - if (attr->inherit && (attr->sample_type & PERF_SAMPLE_GROUP)) + if (attr->inherit && (attr->read_format & PERF_FORMAT_GROUP)) is a clear fail :/ While this changes user visible behaviour; it was previously possible to create an inherited event with PERF_SAMPLE_READ; this is deemed acceptible because its results were always incorrect. Reported-by: Andi Kleen Signed-off-by: Peter Zijlstra (Intel) Cc: Alexander Shishkin Cc: Arnaldo Carvalho de Melo Cc: Jiri Olsa Cc: Linus Torvalds Cc: Peter Zijlstra Cc: Stephane Eranian Cc: Thomas Gleixner Cc: Vince Weaver Fixes: 3dab77fb1bf8 ("perf: Rework/fix the whole read vs group stuff") Link: http://lkml.kernel.org/r/20170530094512.dy2nljns2uq7qa3j@hirez.programming.kicks-ass.net Signed-off-by: Ingo Molnar --- kernel/events/core.c | 15 ++++++++++----- 1 file changed, 10 insertions(+), 5 deletions(-) diff --git a/kernel/events/core.c b/kernel/events/core.c index 3de0b98c4414..407dad6cf89a 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -5729,9 +5729,6 @@ static void perf_output_read_one(struct perf_output_handle *handle, __output_copy(handle, values, n * sizeof(u64)); } -/* - * XXX PERF_FORMAT_GROUP vs inherited events seems difficult. - */ static void perf_output_read_group(struct perf_output_handle *handle, struct perf_event *event, u64 enabled, u64 running) @@ -5776,6 +5773,13 @@ static void perf_output_read_group(struct perf_output_handle *handle, #define PERF_FORMAT_TOTAL_TIMES (PERF_FORMAT_TOTAL_TIME_ENABLED|\ PERF_FORMAT_TOTAL_TIME_RUNNING) +/* + * XXX PERF_SAMPLE_READ vs inherited events seems difficult. + * + * The problem is that its both hard and excessively expensive to iterate the + * child list, not to mention that its impossible to IPI the children running + * on another CPU, from interrupt/NMI context. + */ static void perf_output_read(struct perf_output_handle *handle, struct perf_event *event) { @@ -9462,9 +9466,10 @@ perf_event_alloc(struct perf_event_attr *attr, int cpu, local64_set(&hwc->period_left, hwc->sample_period); /* - * we currently do not support PERF_FORMAT_GROUP on inherited events + * We currently do not support PERF_SAMPLE_READ on inherited events. + * See perf_output_read(). */ - if (attr->inherit && (attr->read_format & PERF_FORMAT_GROUP)) + if (attr->inherit && (attr->sample_type & PERF_SAMPLE_READ)) goto err_ns; if (!has_branch_stack(event))