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cpuset: Honour task_cpu_possible_mask() in guarantee_online_cpus()

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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
This commit is contained in:
Will Deacon 2021-07-30 12:24:30 +01:00 committed by Peter Zijlstra
parent d4b96fb92a
commit 431c69fac0
2 changed files with 27 additions and 18 deletions
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2
include/linux/cpuset.h
View File

@ -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)

43
kernel/cgroup/cpuset.c
View File

@ -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);
}