Messages in this thread Patch in this message | | | From | Mark Rutland <> | Subject | [PATCH] perf tools: session: avoid infinite loop | Date | Wed, 16 Sep 2015 18:18:49 +0100 |
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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.rutland@arm.com> Cc: Adrian Hunter <adrian.hunter@intel.com> Cc: Arnaldo Carvalho de Melo <acme@kernel.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Jiri Olsa <jolsa@redhat.com> Cc: Peter Zijlstra <peterz@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
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