[patch 1/5] sched: fix sign under-flows in wake_affine

Paul Turner
2011-01-22T05:04:42Z

[-- Attachment #1: sched-signed_wake_affine.patch --]
[-- Type: text/plain, Size: 1246 bytes --]

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>

---
kernel/sched_fair.c | 6 +++---
1 file changed, 3 insertions(+), 3 deletions(-)

Index: tip3/kernel/sched_fair.c
===================================================================
--- tip3.orig/kernel/sched_fair.c
+++ tip3/kernel/sched_fair.c
@@ -1404,7 +1404,7 @@ static inline unsigned long effective_lo

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;
@@ -1443,8 +1443,8 @@ static int wake_affine(struct sched_doma
* 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);