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SubjectRe: [PATCH v5 3/5] cgroup/cpuset: make callback_lock raw
Hi Li Zefan and Tejun Heo,

It would be great if you could please have a look at the proposed change
below (and the rest of the set of course :-).

Another bit that I'd be more comfortable after hearing your word on it
is this one (discussed over 5/5):

https://lore.kernel.org/lkml/20180925130750.GA25664@localhost.localdomain/

Best,

- Juri

On 03/09/18 16:27, Juri Lelli wrote:
> callback_lock grants the holder read-only access to cpusets. For fixing
> a synchronization issue between cpusets and scheduler core, it is now
> required to make callback_lock available to core scheduler code.
>
> Convert callback_lock to raw_spin_lock, so that it will be always safe
> to acquire it from atomic context.
>
> Signed-off-by: Juri Lelli <juri.lelli@redhat.com>
> ---
> kernel/cgroup/cpuset.c | 66 +++++++++++++++++++++---------------------
> 1 file changed, 33 insertions(+), 33 deletions(-)
>
> diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
> index 266f10cb7222..5b43f482fa0f 100644
> --- a/kernel/cgroup/cpuset.c
> +++ b/kernel/cgroup/cpuset.c
> @@ -288,7 +288,7 @@ static struct cpuset top_cpuset = {
> */
>
> static DEFINE_MUTEX(cpuset_mutex);
> -static DEFINE_SPINLOCK(callback_lock);
> +static DEFINE_RAW_SPINLOCK(callback_lock);
>
> static struct workqueue_struct *cpuset_migrate_mm_wq;
>
> @@ -922,9 +922,9 @@ static void update_cpumasks_hier(struct cpuset *cs, struct cpumask *new_cpus)
> continue;
> rcu_read_unlock();
>
> - spin_lock_irq(&callback_lock);
> + raw_spin_lock_irq(&callback_lock);
> cpumask_copy(cp->effective_cpus, new_cpus);
> - spin_unlock_irq(&callback_lock);
> + raw_spin_unlock_irq(&callback_lock);
>
> WARN_ON(!is_in_v2_mode() &&
> !cpumask_equal(cp->cpus_allowed, cp->effective_cpus));
> @@ -989,9 +989,9 @@ static int update_cpumask(struct cpuset *cs, struct cpuset *trialcs,
> if (retval < 0)
> return retval;
>
> - spin_lock_irq(&callback_lock);
> + raw_spin_lock_irq(&callback_lock);
> cpumask_copy(cs->cpus_allowed, trialcs->cpus_allowed);
> - spin_unlock_irq(&callback_lock);
> + raw_spin_unlock_irq(&callback_lock);
>
> /* use trialcs->cpus_allowed as a temp variable */
> update_cpumasks_hier(cs, trialcs->cpus_allowed);
> @@ -1175,9 +1175,9 @@ static void update_nodemasks_hier(struct cpuset *cs, nodemask_t *new_mems)
> continue;
> rcu_read_unlock();
>
> - spin_lock_irq(&callback_lock);
> + raw_spin_lock_irq(&callback_lock);
> cp->effective_mems = *new_mems;
> - spin_unlock_irq(&callback_lock);
> + raw_spin_unlock_irq(&callback_lock);
>
> WARN_ON(!is_in_v2_mode() &&
> !nodes_equal(cp->mems_allowed, cp->effective_mems));
> @@ -1245,9 +1245,9 @@ static int update_nodemask(struct cpuset *cs, struct cpuset *trialcs,
> if (retval < 0)
> goto done;
>
> - spin_lock_irq(&callback_lock);
> + raw_spin_lock_irq(&callback_lock);
> cs->mems_allowed = trialcs->mems_allowed;
> - spin_unlock_irq(&callback_lock);
> + raw_spin_unlock_irq(&callback_lock);
>
> /* use trialcs->mems_allowed as a temp variable */
> update_nodemasks_hier(cs, &trialcs->mems_allowed);
> @@ -1338,9 +1338,9 @@ static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
> spread_flag_changed = ((is_spread_slab(cs) != is_spread_slab(trialcs))
> || (is_spread_page(cs) != is_spread_page(trialcs)));
>
> - spin_lock_irq(&callback_lock);
> + raw_spin_lock_irq(&callback_lock);
> cs->flags = trialcs->flags;
> - spin_unlock_irq(&callback_lock);
> + raw_spin_unlock_irq(&callback_lock);
>
> if (!cpumask_empty(trialcs->cpus_allowed) && balance_flag_changed)
> rebuild_sched_domains_locked();
> @@ -1755,7 +1755,7 @@ static int cpuset_common_seq_show(struct seq_file *sf, void *v)
> cpuset_filetype_t type = seq_cft(sf)->private;
> int ret = 0;
>
> - spin_lock_irq(&callback_lock);
> + raw_spin_lock_irq(&callback_lock);
>
> switch (type) {
> case FILE_CPULIST:
> @@ -1774,7 +1774,7 @@ static int cpuset_common_seq_show(struct seq_file *sf, void *v)
> ret = -EINVAL;
> }
>
> - spin_unlock_irq(&callback_lock);
> + raw_spin_unlock_irq(&callback_lock);
> return ret;
> }
>
> @@ -1989,12 +1989,12 @@ static int cpuset_css_online(struct cgroup_subsys_state *css)
>
> cpuset_inc();
>
> - spin_lock_irq(&callback_lock);
> + raw_spin_lock_irq(&callback_lock);
> if (is_in_v2_mode()) {
> cpumask_copy(cs->effective_cpus, parent->effective_cpus);
> cs->effective_mems = parent->effective_mems;
> }
> - spin_unlock_irq(&callback_lock);
> + raw_spin_unlock_irq(&callback_lock);
>
> if (!test_bit(CGRP_CPUSET_CLONE_CHILDREN, &css->cgroup->flags))
> goto out_unlock;
> @@ -2021,12 +2021,12 @@ static int cpuset_css_online(struct cgroup_subsys_state *css)
> }
> rcu_read_unlock();
>
> - spin_lock_irq(&callback_lock);
> + raw_spin_lock_irq(&callback_lock);
> cs->mems_allowed = parent->mems_allowed;
> cs->effective_mems = parent->mems_allowed;
> cpumask_copy(cs->cpus_allowed, parent->cpus_allowed);
> cpumask_copy(cs->effective_cpus, parent->cpus_allowed);
> - spin_unlock_irq(&callback_lock);
> + raw_spin_unlock_irq(&callback_lock);
> out_unlock:
> mutex_unlock(&cpuset_mutex);
> return 0;
> @@ -2065,7 +2065,7 @@ static void cpuset_css_free(struct cgroup_subsys_state *css)
> static void cpuset_bind(struct cgroup_subsys_state *root_css)
> {
> mutex_lock(&cpuset_mutex);
> - spin_lock_irq(&callback_lock);
> + raw_spin_lock_irq(&callback_lock);
>
> if (is_in_v2_mode()) {
> cpumask_copy(top_cpuset.cpus_allowed, cpu_possible_mask);
> @@ -2076,7 +2076,7 @@ static void cpuset_bind(struct cgroup_subsys_state *root_css)
> top_cpuset.mems_allowed = top_cpuset.effective_mems;
> }
>
> - spin_unlock_irq(&callback_lock);
> + raw_spin_unlock_irq(&callback_lock);
> mutex_unlock(&cpuset_mutex);
> }
>
> @@ -2174,12 +2174,12 @@ hotplug_update_tasks_legacy(struct cpuset *cs,
> {
> bool is_empty;
>
> - spin_lock_irq(&callback_lock);
> + raw_spin_lock_irq(&callback_lock);
> cpumask_copy(cs->cpus_allowed, new_cpus);
> cpumask_copy(cs->effective_cpus, new_cpus);
> cs->mems_allowed = *new_mems;
> cs->effective_mems = *new_mems;
> - spin_unlock_irq(&callback_lock);
> + raw_spin_unlock_irq(&callback_lock);
>
> /*
> * Don't call update_tasks_cpumask() if the cpuset becomes empty,
> @@ -2216,10 +2216,10 @@ hotplug_update_tasks(struct cpuset *cs,
> if (nodes_empty(*new_mems))
> *new_mems = parent_cs(cs)->effective_mems;
>
> - spin_lock_irq(&callback_lock);
> + raw_spin_lock_irq(&callback_lock);
> cpumask_copy(cs->effective_cpus, new_cpus);
> cs->effective_mems = *new_mems;
> - spin_unlock_irq(&callback_lock);
> + raw_spin_unlock_irq(&callback_lock);
>
> if (cpus_updated)
> update_tasks_cpumask(cs);
> @@ -2312,21 +2312,21 @@ static void cpuset_hotplug_workfn(struct work_struct *work)
>
> /* synchronize cpus_allowed to cpu_active_mask */
> if (cpus_updated) {
> - spin_lock_irq(&callback_lock);
> + raw_spin_lock_irq(&callback_lock);
> if (!on_dfl)
> cpumask_copy(top_cpuset.cpus_allowed, &new_cpus);
> cpumask_copy(top_cpuset.effective_cpus, &new_cpus);
> - spin_unlock_irq(&callback_lock);
> + raw_spin_unlock_irq(&callback_lock);
> /* we don't mess with cpumasks of tasks in top_cpuset */
> }
>
> /* synchronize mems_allowed to N_MEMORY */
> if (mems_updated) {
> - spin_lock_irq(&callback_lock);
> + raw_spin_lock_irq(&callback_lock);
> if (!on_dfl)
> top_cpuset.mems_allowed = new_mems;
> top_cpuset.effective_mems = new_mems;
> - spin_unlock_irq(&callback_lock);
> + raw_spin_unlock_irq(&callback_lock);
> update_tasks_nodemask(&top_cpuset);
> }
>
> @@ -2425,11 +2425,11 @@ void cpuset_cpus_allowed(struct task_struct *tsk, struct cpumask *pmask)
> {
> unsigned long flags;
>
> - spin_lock_irqsave(&callback_lock, flags);
> + raw_spin_lock_irqsave(&callback_lock, flags);
> rcu_read_lock();
> guarantee_online_cpus(task_cs(tsk), pmask);
> rcu_read_unlock();
> - spin_unlock_irqrestore(&callback_lock, flags);
> + raw_spin_unlock_irqrestore(&callback_lock, flags);
> }
>
> void cpuset_cpus_allowed_fallback(struct task_struct *tsk)
> @@ -2477,11 +2477,11 @@ nodemask_t cpuset_mems_allowed(struct task_struct *tsk)
> nodemask_t mask;
> unsigned long flags;
>
> - spin_lock_irqsave(&callback_lock, flags);
> + raw_spin_lock_irqsave(&callback_lock, flags);
> rcu_read_lock();
> guarantee_online_mems(task_cs(tsk), &mask);
> rcu_read_unlock();
> - spin_unlock_irqrestore(&callback_lock, flags);
> + raw_spin_unlock_irqrestore(&callback_lock, flags);
>
> return mask;
> }
> @@ -2573,14 +2573,14 @@ bool __cpuset_node_allowed(int node, gfp_t gfp_mask)
> return true;
>
> /* Not hardwall and node outside mems_allowed: scan up cpusets */
> - spin_lock_irqsave(&callback_lock, flags);
> + raw_spin_lock_irqsave(&callback_lock, flags);
>
> rcu_read_lock();
> cs = nearest_hardwall_ancestor(task_cs(current));
> allowed = node_isset(node, cs->mems_allowed);
> rcu_read_unlock();
>
> - spin_unlock_irqrestore(&callback_lock, flags);
> + raw_spin_unlock_irqrestore(&callback_lock, flags);
> return allowed;
> }
>
> --
> 2.17.1
>

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