[PATCH] perf record: Fix poll return value propagation

From: Jiri Olsa
Date: Mon Jun 02 2014 - 14:02:30 EST

If the perf record command is interrupted in record__mmap_read_all
function, the 'done' is set and err has the latest poll return
value, which is most likely positive number (= number of pollfds
ready to read).

This 'positive err' is then propagated to the exit code, resulting
in not finishing the perf.data header properly, causing following
error in report:

# perf record -F 50000 -a

make the system real busy, so there's more chance
to interrupt perf in event writing code

^C[ perf record: Woken up 16 times to write data ]
[ perf record: Captured and wrote 30.292 MB perf.data (~1323468 samples) ]

# perf report --stdio > /dev/null
WARNING: The perf.data file's data size field is 0 which is unexpected.
Was the 'perf record' command properly terminated?

Fixing this by checking for positive poll return value
and setting err to 0.

Cc: Arnaldo Carvalho de Melo <acme@xxxxxxxxxx>
Cc: Corey Ashford <cjashfor@xxxxxxxxxxxxxxxxxx>
Cc: David Ahern <dsahern@xxxxxxxxx>
Cc: Frederic Weisbecker <fweisbec@xxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Namhyung Kim <namhyung@xxxxxxxxxx>
Cc: Paul Mackerras <paulus@xxxxxxxxx>
Cc: Peter Zijlstra <a.p.zijlstra@xxxxxxxxx>
Signed-off-by: Jiri Olsa <jolsa@xxxxxxxxxx>
tools/perf/builtin-record.c | 6 +++++-
1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/tools/perf/builtin-record.c b/tools/perf/builtin-record.c
index e4c85b8..ce2cfec 100644
--- a/tools/perf/builtin-record.c
+++ b/tools/perf/builtin-record.c
@@ -454,7 +454,11 @@ static int __cmd_record(struct record *rec, int argc, const char **argv)
if (done)
err = poll(rec->evlist->pollfd, rec->evlist->nr_fds, -1);
- if (err < 0 && errno == EINTR)
+ /*
+ * Propagate error, only if there's any. Ignore positive
+ * number of returned events and interrupt error.
+ */
+ if (err > 0 || (err < 0 && errno == EINTR))
err = 0;

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