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Subject[patch 125/164] perf: Fix signed comparison in perf_adjust_period()
2.6.33-stable review patch.  If anyone has any objections, please let me know.


From: Peter Zijlstra <>

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 <>
Tested-by: Frederic Weisbecker <>
Signed-off-by: Peter Zijlstra <>
LKML-Reference: <new-submission>
Signed-off-by: Ingo Molnar <>
Signed-off-by: Greg Kroah-Hartman <>

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);

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