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sched: Fix sign under-flows in wake_affine

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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>
This commit is contained in:
Paul Turner 2011-01-21 20:44:59 -08:00 committed by Ingo Molnar
parent 6663050edd
commit e37b6a7b27
1 changed files with 3 additions and 3 deletions
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6
kernel/sched_fair.c
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@ -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);