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Date: Wed, 19 Apr 2023 02:48:32 +0000
From: Yang Jihong <yangjihong1@...wei.com>
To: <peterz@...radead.org>, <mingo@...hat.com>, <acme@...nel.org>,
<mark.rutland@....com>, <alexander.shishkin@...ux.intel.com>,
<jolsa@...nel.org>, <namhyung@...nel.org>, <irogers@...gle.com>,
<adrian.hunter@...el.com>, <linux-perf-users@...r.kernel.org>,
<linux-kernel@...r.kernel.org>
CC: <yangjihong1@...wei.com>
Subject: [PATCH v2] perf/core: Fix perf_sample_data not properly initialized for different swevents in perf_tp_event()
data->sample_flags may be modified in perf_prepare_sample(),
in perf_tp_event(), different swevents use the same on-stack
perf_sample_data, the previous swevent may change sample_flags in
perf_prepare_sample(), as a result, some members of perf_sample_data are
not correctly initialized when next swevent_event preparing sample
(for example data->id, the value varies according to swevent).
A simple scenario triggers this problem is as follows:
# perf record -e sched:sched_switch --switch-output-event sched:sched_switch -a sleep 1
[ perf record: dump data: Woken up 0 times ]
[ perf record: Dump perf.data.2023041209014396 ]
[ perf record: dump data: Woken up 0 times ]
[ perf record: Dump perf.data.2023041209014662 ]
[ perf record: dump data: Woken up 0 times ]
[ perf record: Dump perf.data.2023041209014910 ]
[ perf record: Woken up 0 times to write data ]
[ perf record: Dump perf.data.2023041209015164 ]
[ perf record: Captured and wrote 0.069 MB perf.data.<timestamp> ]
# ls -l
total 860
-rw------- 1 root root 95694 Apr 12 09:01 perf.data.2023041209014396
-rw------- 1 root root 606430 Apr 12 09:01 perf.data.2023041209014662
-rw------- 1 root root 82246 Apr 12 09:01 perf.data.2023041209014910
-rw------- 1 root root 82342 Apr 12 09:01 perf.data.2023041209015164
# perf script -i perf.data.2023041209014396
0x11d58 [0x80]: failed to process type: 9 [Bad address]
Solution: Re-initialize perf_sample_data before processing different swevents.
After fix:
# perf record -e sched:sched_switch --switch-output-event sched:sched_switch -a sleep 1
[ perf record: dump data: Woken up 0 times ]
[ perf record: Dump perf.data.2023041209442259 ]
[ perf record: dump data: Woken up 0 times ]
[ perf record: Dump perf.data.2023041209442514 ]
[ perf record: dump data: Woken up 0 times ]
[ perf record: Dump perf.data.2023041209442760 ]
[ perf record: Woken up 0 times to write data ]
[ perf record: Dump perf.data.2023041209443003 ]
[ perf record: Captured and wrote 0.069 MB perf.data.<timestamp> ]
# ls -l
total 864
-rw------- 1 root root 100166 Apr 12 09:44 perf.data.2023041209442259
-rw------- 1 root root 606438 Apr 12 09:44 perf.data.2023041209442514
-rw------- 1 root root 82246 Apr 12 09:44 perf.data.2023041209442760
-rw------- 1 root root 82342 Apr 12 09:44 perf.data.2023041209443003
# perf script -i perf.data.2023041209442259 | head -n 5
perf 232 [000] 66.846217: sched:sched_switch: prev_comm=perf prev_pid=232 prev_prio=120 prev_state=D ==> next_comm=perf next_pid=234 next_prio=120
perf 234 [000] 66.846449: sched:sched_switch: prev_comm=perf prev_pid=234 prev_prio=120 prev_state=S ==> next_comm=perf next_pid=232 next_prio=120
perf 232 [000] 66.846546: sched:sched_switch: prev_comm=perf prev_pid=232 prev_prio=120 prev_state=R ==> next_comm=perf next_pid=234 next_prio=120
perf 234 [000] 66.846606: sched:sched_switch: prev_comm=perf prev_pid=234 prev_prio=120 prev_state=S ==> next_comm=perf next_pid=232 next_prio=120
perf 232 [000] 66.846646: sched:sched_switch: prev_comm=perf prev_pid=232 prev_prio=120 prev_state=R ==> next_comm=perf next_pid=234 next_prio=120
Fixes: bb447c27a467 ("perf/core: Set data->sample_flags in perf_prepare_sample()")
Signed-off-by: Yang Jihong <yangjihong1@...wei.com>
---
kernel/events/core.c | 16 ++++++++++++----
1 file changed, 12 insertions(+), 4 deletions(-)
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 435815d3be3f..6c4356ad453f 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -10144,14 +10144,22 @@ void perf_tp_event(u16 event_type, u64 count, void *record, int entry_size,
},
};
- perf_sample_data_init(&data, 0, 0);
- perf_sample_save_raw_data(&data, &raw);
-
perf_trace_buf_update(record, event_type);
hlist_for_each_entry_rcu(event, head, hlist_entry) {
- if (perf_tp_event_match(event, &data, regs))
+ if (perf_tp_event_match(event, &data, regs)) {
+ /*
+ * Here use the same on-stack perf_sample_data,
+ * some members in data are event-specific and
+ * need to be re-computed for different sweveents.
+ * Re-initialize data->sample_flags each time safely
+ * to avoid the problem that next event skips preparing
+ * data because data->sample_flags is set.
+ */
+ perf_sample_data_init(&data, 0, 0);
+ perf_sample_save_raw_data(&data, &raw);
perf_swevent_event(event, count, &data, regs);
+ }
}
/*
--
2.30.GIT
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