3.16.61-rc1 review patch. If anyone has any objections, please let me know.
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From: Song Liu songliubraving@fb.com
commit a1150c202207cc8501bebc45b63c264f91959260 upstream.
When hw and sw events are mixed in the same group, they are all attached to the hw perf_event_context. This sometimes requires moving group of perf_event to a different context.
We found a bug in how the kernel handles this, for example if we do:
perf stat -e '{faults,ref-cycles,faults}' -I 1000
1.005591180 1,297 faults 1.005591180 457,476,576 ref-cycles 1.005591180 <not supported> faults
First, sw event "faults" is attached to the sw context, and becomes the group leader. Then, hw event "ref-cycles" is attached, so both events are moved to the hw context. Last, another sw "faults" tries to attach, but it fails because of mismatch between the new target ctx (from sw pmu) and the group_leader's ctx (hw context, same as ref-cycles).
The broken condition is: group_leader is sw event; group_leader is on hw context; add a sw event to the group.
Fix this scenario by checking group_leader's context (instead of just event type). If group_leader is on hw context, use the ->pmu of this context to look up context for the new event.
Signed-off-by: Song Liu songliubraving@fb.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Cc: kernel-team@fb.com Cc: Alexander Shishkin alexander.shishkin@linux.intel.com Cc: Arnaldo Carvalho de Melo acme@redhat.com Cc: Jiri Olsa jolsa@redhat.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Peter Zijlstra peterz@infradead.org Cc: Stephane Eranian eranian@google.com Cc: Thomas Gleixner tglx@linutronix.de Cc: Vince Weaver vincent.weaver@maine.edu Fixes: b04243ef7006 ("perf: Complete software pmu grouping") Link: http://lkml.kernel.org/r/20180503194716.162815-1-songliubraving@fb.com Signed-off-by: Ingo Molnar mingo@kernel.org [bwh: Backported to 3.16: adjust context] Signed-off-by: Ben Hutchings ben@decadent.org.uk --- include/linux/perf_event.h | 8 ++++++++ kernel/events/core.c | 21 +++++++++++---------- 2 files changed, 19 insertions(+), 10 deletions(-)
--- a/include/linux/perf_event.h +++ b/include/linux/perf_event.h @@ -640,6 +640,14 @@ static inline int is_software_event(stru return event->pmu->task_ctx_nr == perf_sw_context; }
+/* + * Return 1 for event in sw context, 0 for event in hw context + */ +static inline int in_software_context(struct perf_event *event) +{ + return event->ctx->pmu->task_ctx_nr == perf_sw_context; +} + extern struct static_key perf_swevent_enabled[PERF_COUNT_SW_MAX];
extern void ___perf_sw_event(u32, u64, struct pt_regs *, u64); --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -7502,19 +7502,20 @@ SYSCALL_DEFINE5(perf_event_open, */ pmu = event->pmu;
- if (group_leader && - (is_software_event(event) != is_software_event(group_leader))) { - if (is_software_event(event)) { + if (group_leader) { + if (is_software_event(event) && + !in_software_context(group_leader)) { /* - * If event and group_leader are not both a software - * event, and event is, then group leader is not. + * If the event is a sw event, but the group_leader + * is on hw context. * - * Allow the addition of software events to !software - * groups, this is safe because software events never - * fail to schedule. + * Allow the addition of software events to hw + * groups, this is safe because software events + * never fail to schedule. */ - pmu = group_leader->pmu; - } else if (is_software_event(group_leader) && + pmu = group_leader->ctx->pmu; + } else if (!is_software_event(event) && + is_software_event(group_leader) && (group_leader->group_flags & PERF_GROUP_SOFTWARE)) { /* * In case the group is a pure software group, and we