[patch 125/164] perf: Fix signed comparison in perf_adjust_period()
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From: Greg KH on 1 Jul 2010 17:00 2.6.33-stable review patch. If anyone has any objections, please let me know. ------------------ From: Peter Zijlstra <a.p.zijlstra(a)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(a)gmail.com> Tested-by: Frederic Weisbecker <fweisbec(a)gmail.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra(a)chello.nl> LKML-Reference: <new-submission> Signed-off-by: Ingo Molnar <mingo(a)elte.hu> Signed-off-by: Greg Kroah-Hartman <gregkh(a)suse.de> --- kernel/perf_event.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) --- a/kernel/perf_event.c +++ b/kernel/perf_event.c @@ -1417,13 +1417,16 @@ do { \ divisor = nsec * frequency; } + if (!divisor) + return dividend; + return div64_u64(dividend, divisor); } 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); -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |