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
