diff options
Diffstat (limited to 'include')
| -rw-r--r-- | include/linux/sched/topology.h | 24 |
1 files changed, 18 insertions, 6 deletions
diff --git a/include/linux/sched/topology.h b/include/linux/sched/topology.h index 51c29581f15e..36553e14866d 100644 --- a/include/linux/sched/topology.h +++ b/include/linux/sched/topology.h @@ -142,18 +142,30 @@ struct sched_domain { unsigned int span_weight; /* - * Span of all CPUs in this domain. + * See sched_domain_span(), on why flex arrays are broken. * - * NOTE: this field is variable length. (Allocated dynamically - * by attaching extra space to the end of the structure, - * depending on how many CPUs the kernel has booted up with) - */ unsigned long span[]; + */ }; static inline struct cpumask *sched_domain_span(struct sched_domain *sd) { - return to_cpumask(sd->span); + /* + * Turns out that C flexible arrays are fundamentally broken since it + * is allowed for offsetof(*sd, span) < sizeof(*sd), this means that + * structure initialzation *sd = { ... }; which writes every byte + * inside sizeof(*type), will over-write the start of the flexible + * array. + * + * Luckily, the way we allocate sched_domain is by: + * + * sizeof(*sd) + cpumask_size() + * + * this means that we have sufficient space for the whole flex array + * *outside* of sizeof(*sd). So use that, and avoid using sd->span. + */ + unsigned long *bitmap = (void *)sd + sizeof(*sd); + return to_cpumask(bitmap); } extern void partition_sched_domains(int ndoms_new, cpumask_var_t doms_new[], |