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cpuset: Honour task_cpu_possible_mask() in guarantee_online_cpus()
Asymmetric systems may not offer the same level of userspace ISA support across all CPUs, meaning that some applications cannot be executed by some CPUs. As a concrete example, upcoming arm64 big.LITTLE designs do not feature support for 32-bit applications on both clusters. Modify guarantee_online_cpus() to take task_cpu_possible_mask() into account when trying to find a suitable set of online CPUs for a given task. This will avoid passing an invalid mask to set_cpus_allowed_ptr() during ->attach() and will subsequently allow the cpuset hierarchy to be taken into account when forcefully overriding the affinity mask for a task which requires migration to a compatible CPU. Signed-off-by: Will Deacon <will@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Valentin Schneider <Valentin.Schneider@arm.com> Link: https://lkml.kernel.org/r/20210730112443.23245-4-will@kernel.org
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@ -185,7 +185,7 @@ static inline void cpuset_read_unlock(void) { }
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static inline void cpuset_cpus_allowed(struct task_struct *p,
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struct cpumask *mask)
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{
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cpumask_copy(mask, cpu_possible_mask);
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cpumask_copy(mask, task_cpu_possible_mask(p));
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}
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static inline void cpuset_cpus_allowed_fallback(struct task_struct *p)
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@ -372,18 +372,29 @@ static inline bool is_in_v2_mode(void)
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}
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/*
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* Return in pmask the portion of a cpusets's cpus_allowed that
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* are online. If none are online, walk up the cpuset hierarchy
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* until we find one that does have some online cpus.
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* Return in pmask the portion of a task's cpusets's cpus_allowed that
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* are online and are capable of running the task. If none are found,
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* walk up the cpuset hierarchy until we find one that does have some
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* appropriate cpus.
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*
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* One way or another, we guarantee to return some non-empty subset
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* of cpu_online_mask.
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*
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* Call with callback_lock or cpuset_mutex held.
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*/
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static void guarantee_online_cpus(struct cpuset *cs, struct cpumask *pmask)
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static void guarantee_online_cpus(struct task_struct *tsk,
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struct cpumask *pmask)
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{
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while (!cpumask_intersects(cs->effective_cpus, cpu_online_mask)) {
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const struct cpumask *possible_mask = task_cpu_possible_mask(tsk);
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struct cpuset *cs;
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if (WARN_ON(!cpumask_and(pmask, possible_mask, cpu_online_mask)))
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cpumask_copy(pmask, cpu_online_mask);
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rcu_read_lock();
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cs = task_cs(tsk);
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while (!cpumask_intersects(cs->effective_cpus, pmask)) {
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cs = parent_cs(cs);
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if (unlikely(!cs)) {
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/*
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@ -393,11 +404,13 @@ static void guarantee_online_cpus(struct cpuset *cs, struct cpumask *pmask)
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* cpuset's effective_cpus is on its way to be
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* identical to cpu_online_mask.
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*/
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cpumask_copy(pmask, cpu_online_mask);
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return;
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goto out_unlock;
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}
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}
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cpumask_and(pmask, cs->effective_cpus, cpu_online_mask);
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cpumask_and(pmask, pmask, cs->effective_cpus);
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out_unlock:
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rcu_read_unlock();
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}
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/*
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@ -2199,15 +2212,13 @@ static void cpuset_attach(struct cgroup_taskset *tset)
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percpu_down_write(&cpuset_rwsem);
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/* prepare for attach */
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if (cs == &top_cpuset)
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cpumask_copy(cpus_attach, cpu_possible_mask);
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else
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guarantee_online_cpus(cs, cpus_attach);
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guarantee_online_mems(cs, &cpuset_attach_nodemask_to);
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cgroup_taskset_for_each(task, css, tset) {
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if (cs != &top_cpuset)
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guarantee_online_cpus(task, cpus_attach);
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else
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cpumask_copy(cpus_attach, task_cpu_possible_mask(task));
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/*
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* can_attach beforehand should guarantee that this doesn't
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* fail. TODO: have a better way to handle failure here
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@ -3302,9 +3313,7 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
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unsigned long flags;
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spin_lock_irqsave(&callback_lock, flags);
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rcu_read_lock();
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guarantee_online_cpus(task_cs(tsk), pmask);
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rcu_read_unlock();
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guarantee_online_cpus(tsk, pmask);
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spin_unlock_irqrestore(&callback_lock, flags);
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}
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