If a session contains no events, we can get stuck in an infinite loop in
__perf_session__process_events, with a non-zero file_size and
data_offset, but a zero data_size.
In this case, we can mmap the entirety of the file (consisting of the
file and attribute headers), and fetch_mmaped_event will correctly
refuse to read any (unmapped and non-existent) event headers. This
causes __perf_session__process_events to unmap the file and retry with
the exact same parameters, getting stuck in an infinite loop.
This has been observed to result in an exit-time hang when counting
rare/unschedulable events with perf record, and can be triggered
artificially with the script below:
----
#!/bin/sh
printf "REPRO: launching perf\n";
./perf record -e software/config=9/ sleep 1 &
PERF_PID=$!;
sleep 0.002;
kill -2 $PERF_PID;
printf "REPRO: waiting for perf (%d) to exit...\n" "$PERF_PID";
wait $PERF_PID;
printf "REPRO: perf exited\n";
----
To avoid this, have __perf_session__process_events bail out early when
the file has no data (i.e. it has no events).
Signed-off-by: Mark Rutland <mark.rutl...@arm.com>
Cc: Adrian Hunter <adrian.hun...@intel.com>
Cc: Arnaldo Carvalho de Melo <a...@kernel.org>
Cc: Ingo Molnar <mi...@redhat.com>
Cc: Jiri Olsa <jo...@redhat.com>
Cc: Peter Zijlstra <pet...@infradead.org>
---
tools/perf/util/session.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/tools/perf/util/session.c b/tools/perf/util/session.c
index 8a4537e..fc3f7c9 100644
--- a/tools/perf/util/session.c
+++ b/tools/perf/util/session.c
@@ -1580,7 +1580,10 @@ static int __perf_session__process_events(struct
perf_session *session,
file_offset = page_offset;
head = data_offset - page_offset;
- if (data_size && (data_offset + data_size < file_size))
+ if (data_size == 0)
+ goto out;
+
+ if (data_offset + data_size < file_size)
file_size = data_offset + data_size;
ui_progress__init(&prog, file_size, "Processing events...");
--
1.9.1
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
