Commit 431c69fa authored by Will Deacon's avatar Will Deacon Committed by Peter Zijlstra
Browse files

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: default avatarWill Deacon <will@kernel.org>
Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: default avatarValentin Schneider <Valentin.Schneider@arm.com>
Link: https://lkml.kernel.org/r/20210730112443.23245-4-will@kernel.org
parent d4b96fb9

include/linux/cpuset.h

+1 −1
Original line number Diff line number Diff line
@@ -185,7 +185,7 @@ static inline void cpuset_read_unlock(void) { } 
static inline void cpuset_cpus_allowed(struct task_struct *p,

				       struct cpumask *mask)

{

	cpumask_copy(mask, cpu_possible_mask);

	cpumask_copy(mask, task_cpu_possible_mask(p));

}



static inline void cpuset_cpus_allowed_fallback(struct task_struct *p)

kernel/cgroup/cpuset.c

+26 −17
Original line number Diff line number Diff line
@@ -372,18 +372,29 @@ static inline bool is_in_v2_mode(void) 
}



/*

 * Return in pmask the portion of a cpusets's cpus_allowed that

 * are online.  If none are online, walk up the cpuset hierarchy

 * until we find one that does have some online cpus.

 * Return in pmask the portion of a task's cpusets's cpus_allowed that

 * are online and are capable of running the task.  If none are found,

 * walk up the cpuset hierarchy until we find one that does have some

 * appropriate cpus.

 *

 * One way or another, we guarantee to return some non-empty subset

 * of cpu_online_mask.

 *

 * Call with callback_lock or cpuset_mutex held.

 */

static void guarantee_online_cpus(struct cpuset *cs, struct cpumask *pmask)

static void guarantee_online_cpus(struct task_struct *tsk,

				  struct cpumask *pmask)

{

	while (!cpumask_intersects(cs->effective_cpus, cpu_online_mask)) {

	const struct cpumask *possible_mask = task_cpu_possible_mask(tsk);

	struct cpuset *cs;



	if (WARN_ON(!cpumask_and(pmask, possible_mask, cpu_online_mask)))

		cpumask_copy(pmask, cpu_online_mask);



	rcu_read_lock();

	cs = task_cs(tsk);



	while (!cpumask_intersects(cs->effective_cpus, pmask)) {

		cs = parent_cs(cs);

		if (unlikely(!cs)) {

			/*
@@ -393,11 +404,13 @@ static void guarantee_online_cpus(struct cpuset *cs, struct cpumask *pmask) 
			 * cpuset's effective_cpus is on its way to be

			 * identical to cpu_online_mask.

			 */

			cpumask_copy(pmask, cpu_online_mask);

			return;

			goto out_unlock;

		}

	}

	cpumask_and(pmask, cs->effective_cpus, cpu_online_mask);

	cpumask_and(pmask, pmask, cs->effective_cpus);



out_unlock:

	rcu_read_unlock();

}



/*
@@ -2199,15 +2212,13 @@ static void cpuset_attach(struct cgroup_taskset *tset) 


	percpu_down_write(&cpuset_rwsem);



	/* prepare for attach */

	if (cs == &top_cpuset)

		cpumask_copy(cpus_attach, cpu_possible_mask);

	else

		guarantee_online_cpus(cs, cpus_attach);



	guarantee_online_mems(cs, &cpuset_attach_nodemask_to);



	cgroup_taskset_for_each(task, css, tset) {

		if (cs != &top_cpuset)

			guarantee_online_cpus(task, cpus_attach);

		else

			cpumask_copy(cpus_attach, task_cpu_possible_mask(task));

		/*

		 * can_attach beforehand should guarantee that this doesn't

		 * fail.  TODO: have a better way to handle failure here
@@ -3302,9 +3313,7 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask) 
	unsigned long flags;



	spin_lock_irqsave(&callback_lock, flags);

	rcu_read_lock();

	guarantee_online_cpus(task_cs(tsk), pmask);

	rcu_read_unlock();

	guarantee_online_cpus(tsk, pmask);

	spin_unlock_irqrestore(&callback_lock, flags);

}