diff options
| author | Peter Zijlstra <a.p.zijlstra@chello.nl> | 2010-06-04 15:18:01 +0200 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@suse.de> | 2010-07-05 11:22:51 -0700 |
| commit | 22fc69f9e98416df62729635f702b5459c4d73a5 (patch) | |
| tree | c77ee7c487777715f083b61ad0966a482638935b | |
| parent | ad569e0445c9073a9fd65c18b465dfef1d9bf3b4 (diff) | |
perf: Fix signed comparison in perf_adjust_period()
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>
| -rw-r--r-- | kernel/perf_event.c | 5 |
1 files changed, 4 insertions, 1 deletions
diff --git a/kernel/perf_event.c b/kernel/perf_event.c index 44b4c626907c..8fcebb4ac0f9 100644 --- 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_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); |