From: Jiri Olsa jolsa@redhat.com
[ Upstream commit cd6fb677ce7e460c25bdd66f689734102ec7d642 ]
Some of the scheduling tracepoints allow the perf_tp_event code to write to ring buffer under different cpu than the code is running on.
This results in corrupted ring buffer data demonstrated in following perf commands:
# perf record -e 'sched:sched_switch,sched:sched_wakeup' perf bench sched messaging # Running 'sched/messaging' benchmark: # 20 sender and receiver processes per group # 10 groups == 400 processes run
Total time: 0.383 [sec] [ perf record: Woken up 8 times to write data ] 0x42b890 [0]: failed to process type: -1765585640 [ perf record: Captured and wrote 4.825 MB perf.data (29669 samples) ]
# perf report --stdio 0x42b890 [0]: failed to process type: -1765585640
The reason for the corruption are some of the scheduling tracepoints, that have __perf_task dfined and thus allow to store data to another cpu ring buffer:
sched_waking sched_wakeup sched_wakeup_new sched_stat_wait sched_stat_sleep sched_stat_iowait sched_stat_blocked
The perf_tp_event function first store samples for current cpu related events defined for tracepoint:
hlist_for_each_entry_rcu(event, head, hlist_entry) perf_swevent_event(event, count, &data, regs);
And then iterates events of the 'task' and store the sample for any task's event that passes tracepoint checks:
ctx = rcu_dereference(task->perf_event_ctxp[perf_sw_context]);
list_for_each_entry_rcu(event, &ctx->event_list, event_entry) { if (event->attr.type != PERF_TYPE_TRACEPOINT) continue; if (event->attr.config != entry->type) continue;
perf_swevent_event(event, count, &data, regs); }
Above code can race with same code running on another cpu, ending up with 2 cpus trying to store under the same ring buffer, which is specifically not allowed.
This patch prevents the problem, by allowing only events with the same current cpu to receive the event.
NOTE: this requires the use of (per-task-)per-cpu buffers for this feature to work; perf-record does this.
Signed-off-by: Jiri Olsa jolsa@kernel.org [peterz: small edits to Changelog] Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Cc: Alexander Shishkin alexander.shishkin@linux.intel.com Cc: Andrew Vagin avagin@openvz.org Cc: Arnaldo Carvalho de Melo acme@kernel.org Cc: Arnaldo Carvalho de Melo acme@redhat.com Cc: Jiri Olsa jolsa@redhat.com Cc: Linus Torvalds torvalds@linux-foundation.org Cc: Namhyung Kim namhyung@kernel.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: e6dab5ffab59 ("perf/trace: Add ability to set a target task for events") Link: http://lkml.kernel.org/r/20180923161343.GB15054@krava Signed-off-by: Ingo Molnar mingo@kernel.org Signed-off-by: Sasha Levin sashal@kernel.org --- kernel/events/core.c | 2 ++ 1 file changed, 2 insertions(+)
diff --git a/kernel/events/core.c b/kernel/events/core.c index b1ed5e99d9c6..fc072b7f839d 100644 --- a/kernel/events/core.c +++ b/kernel/events/core.c @@ -8319,6 +8319,8 @@ void perf_tp_event(u16 event_type, u64 count, void *record, int entry_size, goto unlock;
list_for_each_entry_rcu(event, &ctx->event_list, event_entry) { + if (event->cpu != smp_processor_id()) + continue; if (event->attr.type != PERF_TYPE_TRACEPOINT) continue; if (event->attr.config != entry->type)