From f6ab91add6355e231e1c47897027b2a6ee4fa268 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Fri, 4 Jun 2010 15:18:01 +0200 Subject: [PATCH] perf: Fix signed comparison in perf_adjust_period() 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 Tested-by: Frederic Weisbecker Signed-off-by: Peter Zijlstra Cc: LKML-Reference: Signed-off-by: Ingo Molnar --- kernel/perf_event.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/kernel/perf_event.c b/kernel/perf_event.c index 31d6afe92594..ff86c558af4c 100644 --- a/kernel/perf_event.c +++ b/kernel/perf_event.c @@ -1507,6 +1507,9 @@ do { \ divisor = nsec * frequency; } + if (!divisor) + return dividend; + return div64_u64(dividend, divisor); } @@ -1529,7 +1532,7 @@ static int perf_event_start(struct perf_event *event) 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); -- 2.20.1