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Commit aa24163b authored by Prateek Sood's avatar Prateek Sood Committed by Tejun Heo
Browse files

cgroup/cpuset: remove circular dependency deadlock 



Remove circular dependency deadlock in a scenario where hotplug of CPU is
being done while there is updation in cgroup and cpuset triggered from
userspace.

Process A => kthreadd => Process B => Process C => Process A

Process A
cpu_subsys_offline();
  cpu_down();
    _cpu_down();
      percpu_down_write(&cpu_hotplug_lock); //held
      cpuhp_invoke_callback();
	     workqueue_offline_cpu();
            queue_work_on(); // unbind_work on system_highpri_wq
               __queue_work();
                 insert_work();
                    wake_up_worker();
            flush_work();
               wait_for_completion();

worker_thread();
   manage_workers();
      create_worker();
	     kthread_create_on_node();
		    wake_up_process(kthreadd_task);

kthreadd
kthreadd();
  kernel_thread();
    do_fork();
      copy_process();
        percpu_down_read(&cgroup_threadgroup_rwsem);
          __rwsem_down_read_failed_common(); //waiting

Process B
kernfs_fop_write();
  cgroup_file_write();
    cgroup_procs_write();
      percpu_down_write(&cgroup_threadgroup_rwsem); //held
      cgroup_attach_task();
        cgroup_migrate();
          cgroup_migrate_execute();
            cpuset_can_attach();
              mutex_lock(&cpuset_mutex); //waiting

Process C
kernfs_fop_write();
  cgroup_file_write();
    cpuset_write_resmask();
      mutex_lock(&cpuset_mutex); //held
      update_cpumask();
        update_cpumasks_hier();
          rebuild_sched_domains_locked();
            get_online_cpus();
              percpu_down_read(&cpu_hotplug_lock); //waiting

Eliminating deadlock by reversing the locking order for cpuset_mutex and
cpu_hotplug_lock.

Signed-off-by: default avatarPrateek Sood <prsood@codeaurora.org>
Signed-off-by: default avatarTejun Heo <tj@kernel.org>
parent 4fbd8d19

kernel/cgroup/cpuset.c

+30 −23
Original line number Diff line number Diff line
@@ -812,6 +812,18 @@ static int generate_sched_domains(cpumask_var_t **domains, 
	return ndoms;

}



static void cpuset_sched_change_begin(void)

{

	cpus_read_lock();

	mutex_lock(&cpuset_mutex);

}



static void cpuset_sched_change_end(void)

{

	mutex_unlock(&cpuset_mutex);

	cpus_read_unlock();

}



/*

 * Rebuild scheduler domains.

 *
@@ -821,16 +833,14 @@ static int generate_sched_domains(cpumask_var_t **domains, 
 * 'cpus' is removed, then call this routine to rebuild the

 * scheduler's dynamic sched domains.

 *

 * Call with cpuset_mutex held.  Takes get_online_cpus().

 */

static void rebuild_sched_domains_locked(void)

static void rebuild_sched_domains_cpuslocked(void)

{

	struct sched_domain_attr *attr;

	cpumask_var_t *doms;

	int ndoms;



	lockdep_assert_held(&cpuset_mutex);

	get_online_cpus();



	/*

	 * We have raced with CPU hotplug. Don't do anything to avoid
@@ -838,27 +848,25 @@ static void rebuild_sched_domains_locked(void) 
	 * Anyways, hotplug work item will rebuild sched domains.

	 */

	if (!cpumask_equal(top_cpuset.effective_cpus, cpu_active_mask))

		goto out;

		return;



	/* Generate domain masks and attrs */

	ndoms = generate_sched_domains(&doms, &attr);



	/* Have scheduler rebuild the domains */

	partition_sched_domains(ndoms, doms, attr);

out:

	put_online_cpus();

}

#else /* !CONFIG_SMP */

static void rebuild_sched_domains_locked(void)

static void rebuild_sched_domains_cpuslocked(void)

{

}

#endif /* CONFIG_SMP */



void rebuild_sched_domains(void)

{

	mutex_lock(&cpuset_mutex);

	rebuild_sched_domains_locked();

	mutex_unlock(&cpuset_mutex);

	cpuset_sched_change_begin();

	rebuild_sched_domains_cpuslocked();

	cpuset_sched_change_end();

}



/**
@@ -944,7 +952,7 @@ static void update_cpumasks_hier(struct cpuset *cs, struct cpumask *new_cpus) 
	rcu_read_unlock();



	if (need_rebuild_sched_domains)

		rebuild_sched_domains_locked();

		rebuild_sched_domains_cpuslocked();

}



/**
@@ -1276,7 +1284,7 @@ static int update_relax_domain_level(struct cpuset *cs, s64 val) 
		cs->relax_domain_level = val;

		if (!cpumask_empty(cs->cpus_allowed) &&

		    is_sched_load_balance(cs))

			rebuild_sched_domains_locked();

			rebuild_sched_domains_cpuslocked();

	}



	return 0;
@@ -1309,7 +1317,6 @@ static void update_tasks_flags(struct cpuset *cs) 
 *

 * Call with cpuset_mutex held.

 */



static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs,

		       int turning_on)

{
@@ -1342,7 +1349,7 @@ static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs, 
	spin_unlock_irq(&callback_lock);



	if (!cpumask_empty(trialcs->cpus_allowed) && balance_flag_changed)

		rebuild_sched_domains_locked();

		rebuild_sched_domains_cpuslocked();



	if (spread_flag_changed)

		update_tasks_flags(cs);
@@ -1610,7 +1617,7 @@ static int cpuset_write_u64(struct cgroup_subsys_state *css, struct cftype *cft, 
	cpuset_filetype_t type = cft->private;

	int retval = 0;



	mutex_lock(&cpuset_mutex);

	cpuset_sched_change_begin();

	if (!is_cpuset_online(cs)) {

		retval = -ENODEV;

		goto out_unlock;
@@ -1646,7 +1653,7 @@ static int cpuset_write_u64(struct cgroup_subsys_state *css, struct cftype *cft, 
		break;

	}

out_unlock:

	mutex_unlock(&cpuset_mutex);

	cpuset_sched_change_end();

	return retval;

}
@@ -1657,7 +1664,7 @@ static int cpuset_write_s64(struct cgroup_subsys_state *css, struct cftype *cft, 
	cpuset_filetype_t type = cft->private;

	int retval = -ENODEV;



	mutex_lock(&cpuset_mutex);

	cpuset_sched_change_begin();

	if (!is_cpuset_online(cs))

		goto out_unlock;
@@ -1670,7 +1677,7 @@ static int cpuset_write_s64(struct cgroup_subsys_state *css, struct cftype *cft, 
		break;

	}

out_unlock:

	mutex_unlock(&cpuset_mutex);

	cpuset_sched_change_end();

	return retval;

}
@@ -1709,7 +1716,7 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of, 
	kernfs_break_active_protection(of->kn);

	flush_work(&cpuset_hotplug_work);



	mutex_lock(&cpuset_mutex);

	cpuset_sched_change_begin();

	if (!is_cpuset_online(cs))

		goto out_unlock;
@@ -1733,7 +1740,7 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of, 


	free_trial_cpuset(trialcs);

out_unlock:

	mutex_unlock(&cpuset_mutex);

	cpuset_sched_change_end();

	kernfs_unbreak_active_protection(of->kn);

	css_put(&cs->css);

	flush_workqueue(cpuset_migrate_mm_wq);
@@ -2034,14 +2041,14 @@ static int cpuset_css_online(struct cgroup_subsys_state *css) 
/*

 * If the cpuset being removed has its flag 'sched_load_balance'

 * enabled, then simulate turning sched_load_balance off, which

 * will call rebuild_sched_domains_locked().

 * will call rebuild_sched_domains_cpuslocked().

 */



static void cpuset_css_offline(struct cgroup_subsys_state *css)

{

	struct cpuset *cs = css_cs(css);



	mutex_lock(&cpuset_mutex);

	cpuset_sched_change_begin();



	if (is_sched_load_balance(cs))

		update_flag(CS_SCHED_LOAD_BALANCE, cs, 0);
@@ -2049,7 +2056,7 @@ static void cpuset_css_offline(struct cgroup_subsys_state *css) 
	cpuset_dec();

	clear_bit(CS_ONLINE, &cs->flags);



	mutex_unlock(&cpuset_mutex);

	cpuset_sched_change_end();

}



static void cpuset_css_free(struct cgroup_subsys_state *css)