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authorPeter Zijlstra <a.p.zijlstra@chello.nl>2010-06-04 15:18:01 +0200
committerIngo Molnar <mingo@elte.hu>2010-06-08 18:43:00 +0200
commitf6ab91add6355e231e1c47897027b2a6ee4fa268 (patch)
tree74dffdf3b78c290d38a78b73788dce64e4c1e857
parent58cc1a9e3b11a84e66c4d3a4cc9073f2cb0ecabb (diff)
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 <fweisbec@gmail.com> Tested-by: Frederic Weisbecker <fweisbec@gmail.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Cc: <stable@kernel.org> LKML-Reference: <new-submission> Signed-off-by: Ingo Molnar <mingo@elte.hu>
-rw-r--r--kernel/perf_event.c5
1 files changed, 4 insertions, 1 deletions
diff --git a/kernel/perf_event.c b/kernel/perf_event.c
index 31d6afe9259..ff86c558af4 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);