[PATCH AUTOSEL 4.4 22/25] perf/ring_buffer: Prevent concurent ring buffer access

Sasha Levin
2018-10-16T04:16:32Z

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 990ac41d8a5f..330fcd1b1822 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7018,6 +7018,8 @@ void perf_tp_event(u64 addr, 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)
--
2.17.1