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Date:   Tue, 25 Sep 2018 16:34:16 +0200
From:   Juri Lelli <juri.lelli@...hat.com>
To:     lizefan@...wei.com, tj@...nel.org
Cc:     linux-kernel@...r.kernel.org, luca.abeni@...tannapisa.it,
        claudio@...dence.eu.com, tommaso.cucinotta@...tannapisa.it,
        bristot@...hat.com, mathieu.poirier@...aro.org,
        cgroups@...r.kernel.org, peterz@...radead.org, mingo@...hat.com,
        rostedt@...dmis.org
Subject: Re: [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@...hat.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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