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BACKPORT: FROMLIST: 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.

Cc: Li Zefan <lizefan@huawei.com>
Cc: Tejun Heo <tj@kernel.org>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: Will Deacon <will@kernel.org>
Bug: 178507149
Link: https://lore.kernel.org/linux-arch/20201208132835.6151-9-will@kernel.org/
[will: Fixed conflict due to active_mask being used instead of online_mask]
Signed-off-by: Will Deacon <willdeacon@google.com>
Change-Id: I5b4a50e7a257af928dccd87f1dbd961ea26ff834
This commit is contained in:
Will Deacon
2020-12-07 14:35:35 +00:00
committed by Will Deacon
parent 210463b39c
commit 4045a05f88
2 changed files with 21 additions and 15 deletions
Download Patch File Download Diff File Expand all files Collapse all files

3
include/linux/cpuset.h
View File

@@ -15,6 +15,7 @@
#include <linux/cpumask.h>
#include <linux/nodemask.h>
#include <linux/mm.h>
#include <linux/mmu_context.h>
#include <linux/jump_label.h>
#ifdef CONFIG_CPUSETS
@@ -181,7 +182,7 @@ static inline void cpuset_wait_for_hotplug(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)

33
kernel/cgroup/cpuset.c
View File

@@ -364,18 +364,26 @@ 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_active_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_active_mask)) {
struct cpuset *cs = task_cs(tsk);
const struct cpumask *possible_mask = task_cpu_possible_mask(tsk);
if (WARN_ON(!cpumask_and(pmask, possible_mask, cpu_active_mask)))
cpumask_copy(pmask, cpu_active_mask);
while (!cpumask_intersects(cs->effective_cpus, pmask)) {
cs = parent_cs(cs);
if (unlikely(!cs)) {
/*
@@ -385,11 +393,10 @@ 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_active_mask);
return;
}
}
cpumask_and(pmask, cs->effective_cpus, cpu_active_mask);
cpumask_and(pmask, pmask, cs->effective_cpus);
}
/*
@@ -2211,15 +2218,13 @@ static void cpuset_attach(struct cgroup_taskset *tset)
mutex_lock(&cpuset_mutex);
/* 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
@@ -3317,7 +3322,7 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
spin_lock_irqsave(&callback_lock, flags);
rcu_read_lock();
guarantee_online_cpus(task_cs(tsk), pmask);
guarantee_online_cpus(tsk, pmask);
rcu_read_unlock();
spin_unlock_irqrestore(&callback_lock, flags);
}