[tip:sched/core] sched: Fix sign under-flows in wake_affine

tip-bot for Paul Turner
2011-01-26T12:10:24Z

Commit-ID: e37b6a7b27b400c3aa488db8c6629a05095bc79c
Gitweb: http://git.kernel.org/tip/e37b6a7b27b400c3aa488db8c6629a05095bc79c
Author: Paul Turner <pjt@google.com>
AuthorDate: Fri, 21 Jan 2011 20:44:59 -0800
Committer: Ingo Molnar <mingo@elte.hu>
CommitDate: Wed, 26 Jan 2011 12:31:01 +0100

sched: Fix sign under-flows in wake_affine

While care is taken around the zero-point in effective_load to not exceed
the instantaneous rq->weight, it's still possible (e.g. using wake_idx != 0)
for (load + effective_load) to underflow.

In this case the comparing the unsigned values can result in incorrect balanced
decisions.

Signed-off-by: Paul Turner <pjt@google.com>
Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
LKML-Reference: <20110122044851.734245014@google.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
---
kernel/sched_fair.c | 6 +++---
1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/kernel/sched_fair.c b/kernel/sched_fair.c
index 3547699..ccecfec 100644
--- a/kernel/sched_fair.c
+++ b/kernel/sched_fair.c
@@ -1432,7 +1432,7 @@ static inline unsigned long effective_load(struct task_group *tg, int cpu,

static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
{
- unsigned long this_load, load;
+ s64 this_load, load;
int idx, this_cpu, prev_cpu;
unsigned long tl_per_task;
struct task_group *tg;
@@ -1471,8 +1471,8 @@ static int wake_affine(struct sched_domain *sd, struct task_struct *p, int sync)
* Otherwise check if either cpus are near enough in load to allow this
* task to be woken on this_cpu.
*/
- if (this_load) {
- unsigned long this_eff_load, prev_eff_load;
+ if (this_load > 0) {
+ s64 this_eff_load, prev_eff_load;

this_eff_load = 100;
this_eff_load *= power_of(prev_cpu);