cpudl.elements is an instance that should be protected with a spin lock. Without it, the code would be insane.
Current cpudl_find() has problems like, 1. cpudl.elements[0].cpu might not match with cpudl.elements[0].dl. 2. cpudl.elements[0].dl(u64) might not be referred atomically. 3. Two cpudl_maximum()s might return different values. 4. It's just insane. Signed-off-by: Byungchul Park <byungchul.p...@lge.com> --- kernel/sched/cpudeadline.c | 37 ++++++++++++++++++++++++++++++------- 1 file changed, 30 insertions(+), 7 deletions(-) diff --git a/kernel/sched/cpudeadline.c b/kernel/sched/cpudeadline.c index fba235c..6b67016 100644 --- a/kernel/sched/cpudeadline.c +++ b/kernel/sched/cpudeadline.c @@ -131,16 +131,39 @@ int cpudl_find(struct cpudl *cp, struct task_struct *p, cpumask_and(later_mask, cp->free_cpus, &p->cpus_allowed)) { best_cpu = cpumask_any(later_mask); goto out; - } else if (cpumask_test_cpu(cpudl_maximum(cp), &p->cpus_allowed) && - dl_time_before(dl_se->deadline, cp->elements[0].dl)) { - best_cpu = cpudl_maximum(cp); - if (later_mask) - cpumask_set_cpu(best_cpu, later_mask); + } else { + u64 cpudl_dl; + int cpudl_cpu; + int cpudl_valid; + unsigned long flags; + + /* + * Referring to cp->elements must be atomic ops. + */ + raw_spin_lock_irqsave(&cp->lock, flags); + /* + * No problem even in case of very initial heap tree + * to which no entry has been added yet, since + * cp->elements[0].cpu was initialized to zero and + * cp->elements[0].idx was initialized to IDX_INVALID, + * that means the case will be filtered out at the + * following condition. + */ + cpudl_cpu = cpudl_maximum(cp); + cpudl_dl = cp->elements[0].dl; + cpudl_valid = cp->elements[cpudl_cpu].idx; + raw_spin_unlock_irqrestore(&cp->lock, flags); + + if (cpudl_valid != IDX_INVALID && + cpumask_test_cpu(cpudl_cpu, &p->cpus_allowed) && + dl_time_before(dl_se->deadline, cpudl_dl)) { + best_cpu = cpudl_cpu; + if (later_mask) + cpumask_set_cpu(best_cpu, later_mask); + } } out: - WARN_ON(best_cpu != -1 && !cpu_present(best_cpu)); - return best_cpu; } -- 1.9.1