[PATCH] lib: Fix corruption of denominator in flexible proportions

[Jan Kara]

When racing with CPU hotplug, percpu_counter_sum() can return negative
values for the number of observed events. This confuses fprop_new_period(),
which uses unsigned type and as a result number of events is set to big
*positive* number. From that moment on, things go pear shaped and can result
e.g. in division by zero as denominator is later truncated to 32-bits.

Fix the issue by using a signed type in fprop_new_period(). That makes us
bail out from the function without doing anything (mistakenly) thinking
there are no events to age. That makes aging somewhat inaccurate but getting
accurate data would be rather hard.

Reported-by: Borislav Petkov <bp@xxxxxxxxx>
Reported-by: Srivatsa S. Bhat <srivatsa.bhat@xxxxxxxxxxxxxxxxxx>
Signed-off-by: Jan Kara <jack@xxxxxxx>
---
 lib/flex_proportions.c |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)

diff --git a/lib/flex_proportions.c b/lib/flex_proportions.c
index c785554..ebf3bac 100644
--- a/lib/flex_proportions.c
+++ b/lib/flex_proportions.c
@@ -62,7 +62,7 @@ void fprop_global_destroy(struct fprop_global *p)
  */
 bool fprop_new_period(struct fprop_global *p, int periods)
 {
-	u64 events;
+	s64 events;
 	unsigned long flags;
 
 	local_irq_save(flags);
-- 
1.7.1


--+HP7ph2BbKc20aGI--
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/