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authorMark Rutland <mark.rutland@arm.com>2015-09-16 18:18:49 +0100
committerArnaldo Carvalho de Melo <acme@redhat.com>2015-09-18 12:31:40 -0300
commit381c02f6d8ccad8ed574630f879c40fb59715124 (patch)
tree2442e0e3d5aeb70970f9d20d74ee2ac8e4a69e15 /tools
parentf73e22ab450140830005581c2c7ec389791a1b8d (diff)
downloadop-kernel-dev-381c02f6d8ccad8ed574630f879c40fb59715124.zip
op-kernel-dev-381c02f6d8ccad8ed574630f879c40fb59715124.tar.gz
perf record: Avoid infinite loop at buildid processing with no samples
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). Commiter note: I only managed to reproduce this when setting /proc/sys/kernel/kptr_restrict to '1' and changing the code to purposefully not process any samples and no synthesized samples, i.e. kptr_restrict prevents 'record' from synthesizing the kernel mmaps for vmlinux + modules and since it is a workload started from perf, we don't synthesize mmap/comm records for existing threads. Adrian Hunter managed to reproduce it in his environment tho. Signed-off-by: Mark Rutland <mark.rutland@arm.com> Tested-by: Arnaldo Carvalho de Melo <acme@kernel.org> Tested-by: Adrian Hunter <adrian.hunter@intel.com> Cc: Jiri Olsa <jolsa@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Link: http://lkml.kernel.org/r/1442423929-12253-1-git-send-email-mark.rutland@arm.com Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>
Diffstat (limited to 'tools')
-rw-r--r--tools/perf/util/session.c5
1 files changed, 4 insertions, 1 deletions
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...");
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