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authorTuukka Tikkanen <tuukka.tikkanen@linaro.org>2013-08-14 20:02:36 +0400
committerRafael J. Wysocki <rafael.j.wysocki@intel.com>2013-08-23 02:24:16 +0400
commit0d6a7ffa4cc67cc70bf1f4e24fbb0747632845a2 (patch)
treef551d52b69ba39d22e144c468cf52c4dc73a5afe
parent017099e25fb7e482a249d36a654556d32f601f71 (diff)
downloadlinux-0d6a7ffa4cc67cc70bf1f4e24fbb0747632845a2.tar.xz
cpuidle: Check called function parameter in get_typical_interval()
get_typical_interval() uses int_sqrt() in calculation of standard deviation. The formal parameter of int_sqrt() is unsigned long, which may on some platforms be smaller than the 64 bit unsigned integer used as the actual parameter. The overflow can occur frequently when actual idle period lengths are in hundreds of milliseconds. This patch adds a check for such overflow and rejects the candidate average when an overflow would occur. Signed-off-by: Tuukka Tikkanen <tuukka.tikkanen@linaro.org> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
-rw-r--r--drivers/cpuidle/governors/menu.c18
1 files changed, 13 insertions, 5 deletions
diff --git a/drivers/cpuidle/governors/menu.c b/drivers/cpuidle/governors/menu.c
index f1fadbecfa1b..af7b3f6b260d 100644
--- a/drivers/cpuidle/governors/menu.c
+++ b/drivers/cpuidle/governors/menu.c
@@ -226,18 +226,26 @@ again:
}
}
do_div(stddev, divisor);
- stddev = int_sqrt(stddev);
/*
* The typical interval is obtained when standard deviation is small
* or standard deviation is small compared to the average interval.
*
+ * int_sqrt() formal parameter type is unsigned long. When the
+ * greatest difference to an outlier exceeds ~65 ms * sqrt(divisor)
+ * the resulting squared standard deviation exceeds the input domain
+ * of int_sqrt on platforms where unsigned long is 32 bits in size.
+ * In such case reject the candidate average.
+ *
* Use this result only if there is no timer to wake us up sooner.
*/
- if (((avg > stddev * 6) && (divisor * 4 >= INTERVALS * 3))
+ if (likely(stddev <= ULONG_MAX)) {
+ stddev = int_sqrt(stddev);
+ if (((avg > stddev * 6) && (divisor * 4 >= INTERVALS * 3))
|| stddev <= 20) {
- if (data->expected_us > avg)
- data->predicted_us = avg;
- return;
+ if (data->expected_us > avg)
+ data->predicted_us = avg;
+ return;
+ }
}
/*