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cpuset: Remove unnecessary checks in rebuild_sched_domains_locked 

Commit 406100f3da ("cpuset: fix race between hotplug work and later CPU
offline") added a check for empty effective_cpus in partitions for cgroup
v2. However, this check did not account for remote partitions, which were
introduced later.

After commit 2125c0034c ("cgroup/cpuset: Make cpuset hotplug processing
synchronous"), cpuset hotplug handling is now synchronous. This eliminates
the race condition with subsequent CPU offline operations that the original
check aimed to fix.

Instead of extending the check to support remote partitions, this patch
removes all the redundant effective_cpus check. Additionally, it adds a
check and warning to verify that all generated sched domains consist of
active CPUs, preventing partition_sched_domains from being invoked with
offline CPUs.

Signed-off-by: Chen Ridong <chenridong@huawei.com>
Reviewed-by: Waiman Long <longman@redhat.com>
Signed-off-by: Tejun Heo <tj@kernel.org>
master
Chen Ridong 2025-11-26 09:11:58 +00:00 committed by Tejun Heo
parent 82d7e59ea7
commit 6ee43047e8
1 changed files with 16 additions and 36 deletions
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52
kernel/cgroup/cpuset.c
View File

@ -1103,53 +1103,33 @@ void dl_rebuild_rd_accounting(void)
*/
void rebuild_sched_domains_locked(void)
{
struct cgroup_subsys_state *pos_css;
struct sched_domain_attr *attr;
cpumask_var_t *doms;
struct cpuset *cs;
int ndoms;
int i;
lockdep_assert_cpus_held();
lockdep_assert_held(&cpuset_mutex);
force_sd_rebuild = false;
/*
* If we have raced with CPU hotplug, return early to avoid
* passing doms with offlined cpu to partition_sched_domains().
* Anyways, cpuset_handle_hotplug() will rebuild sched domains.
*
* With no CPUs in any subpartitions, top_cpuset's effective CPUs
* should be the same as the active CPUs, so checking only top_cpuset
* is enough to detect racing CPU offlines.
*/
if (cpumask_empty(subpartitions_cpus) &&
!cpumask_equal(top_cpuset.effective_cpus, cpu_active_mask))
return;
/*
* With subpartition CPUs, however, the effective CPUs of a partition
* root should be only a subset of the active CPUs. Since a CPU in any
* partition root could be offlined, all must be checked.
*/
if (!cpumask_empty(subpartitions_cpus)) {
rcu_read_lock();
cpuset_for_each_descendant_pre(cs, pos_css, &top_cpuset) {
if (!is_partition_valid(cs)) {
pos_css = css_rightmost_descendant(pos_css);
continue;
}
if (!cpumask_subset(cs->effective_cpus,
cpu_active_mask)) {
rcu_read_unlock();
return;
}
}
rcu_read_unlock();
}
/* Generate domain masks and attrs */
ndoms = generate_sched_domains(&doms, &attr);
/*
* cpuset_hotplug_workfn is invoked synchronously now, thus this
* function should not race with CPU hotplug. And the effective CPUs
* must not include any offline CPUs. Passing an offline CPU in the
* doms to partition_sched_domains() will trigger a kernel panic.
*
* We perform a final check here: if the doms contains any
* offline CPUs, a warning is emitted and we return directly to
* prevent the panic.
*/
for (i = 0; i < ndoms; ++i) {
if (WARN_ON_ONCE(!cpumask_subset(doms[i], cpu_active_mask)))
return;
}
/* Have scheduler rebuild the domains */
partition_sched_domains(ndoms, doms, attr);
}