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author | Peter Zijlstra <a.p.zijlstra@chello.nl> | 2010-06-04 15:18:01 +0200 |
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committer | Ingo Molnar <mingo@elte.hu> | 2010-06-08 18:43:00 +0200 |
commit | f6ab91add6355e231e1c47897027b2a6ee4fa268 (patch) | |
tree | 74dffdf3b78c290d38a78b73788dce64e4c1e857 /kernel/perf_event.c | |
parent | 58cc1a9e3b11a84e66c4d3a4cc9073f2cb0ecabb (diff) | |
download | linux-f6ab91add6355e231e1c47897027b2a6ee4fa268.tar.gz linux-f6ab91add6355e231e1c47897027b2a6ee4fa268.tar.bz2 linux-f6ab91add6355e231e1c47897027b2a6ee4fa268.zip |
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>
Diffstat (limited to 'kernel/perf_event.c')
-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 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); |