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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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