| Date | Thu, 01 Jul 2010 10:44:14 -0700 | From | Greg KH <> | Subject | [164/200] perf: Fix signed comparison in perf_adjust_period() |
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2.6.34-stable review patch. If anyone has any objections, please let me know.
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From: Peter Zijlstra <a.p.zijlstra@chello.nl>
commit f6ab91add6355e231e1c47897027b2a6ee4fa268 upstream.
Frederic reported that frequency driven swevents didn't work properly and even caused a division-by-zero error.
It turns out there are two bugs, the division-by-zero comes from a failure to deal with that in perf_calculate_period().
The other was more interesting and turned out to be a wrong comparison in perf_adjust_period(). The comparison was between an s64 and u64 and got implicitly converted to an unsigned comparison. The problem is that period_left is typically < 0, so it ended up being always true.
Cure this by making the local period variables s64.
Reported-by: Frederic Weisbecker <fweisbec@gmail.com> Tested-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> LKML-Reference: <new-submission> Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
--- kernel/perf_event.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)
--- a/kernel/perf_event.c +++ b/kernel/perf_event.c @@ -1456,6 +1456,9 @@ do { \ divisor = nsec * frequency; } + if (!divisor) + return dividend; + return div64_u64(dividend, divisor); } @@ -1478,7 +1481,7 @@ static int perf_event_start(struct perf_ static void perf_adjust_period(struct perf_event *event, u64 nsec, u64 count) { struct hw_perf_event *hwc = &event->hw; - u64 period, sample_period; + s64 period, sample_period; s64 delta; period = perf_calculate_period(event, nsec, count);
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