[164/200] perf: Fix signed comparison in perf_adjust_period()

Greg KH
2010-07-01T21:18:39Z

2.6.34-stable review patch. If anyone has any objections, please let me know.

------------------

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);