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Commit 4209efee authored by Prateek Sood's avatar Prateek Sood Committed by Gerrit - the friendly Code Review server
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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();
       mutex_lock(&cpuhotplug.lock); //held
       __cpu_notify();
         workqueue_cpu_down_callback();
           queue_work_on(system_highpri_wq);
             __queue_work();
               insert_work();
                 wake_up_worker(); //pool->nr_running = 0
           flush_work();
           wait_for_completion();

worker_thread();
  need_more_worker(); // returns true
  manage_workers();
    maybe_create_worker();
	  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_tasks_write();
      percpu_down_write(&cgroup_threadgroup_rwsem); //held
      cgroup_attach_task();
        cgroup_migrate();
          cgroup_taskset_migrate();
            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();
              mutex_lock(&cpuhotplug.lock); //waiting

Eliminate this dependecy by reordering locking of cpuset_mutex
and cpuhotplug.lock.

Change-Id: Ifd76373d717c53b531623a3be76b7d32e0d959fd
Signed-off-by: default avatarPrateek Sood <prsood@codeaurora.org>
parent e4b0f5ba

include/linux/cpu.h

+2 −0
Original line number Diff line number Diff line
@@ -234,6 +234,7 @@ extern struct bus_type cpu_subsys; 
extern void cpu_hotplug_begin(void);

extern void cpu_hotplug_done(void);

extern void get_online_cpus(void);

extern void cpu_hotplug_mutex_held(void);

extern void put_online_cpus(void);

extern void cpu_hotplug_disable(void);

extern void cpu_hotplug_enable(void);
@@ -256,6 +257,7 @@ static inline void cpu_hotplug_done(void) {} 
#define cpu_hotplug_enable()	do { } while (0)

#define hotcpu_notifier(fn, pri)	do { (void)(fn); } while (0)

#define __hotcpu_notifier(fn, pri)	do { (void)(fn); } while (0)

#define cpu_hotplug_mutex_held()	do { } while (0)

/* These aren't inline functions due to a GCC bug. */

#define register_hotcpu_notifier(nb)	({ (void)(nb); 0; })

#define __register_hotcpu_notifier(nb)	({ (void)(nb); 0; })

kernel/cpu.c

+5 −0
Original line number Diff line number Diff line
@@ -91,6 +91,11 @@ static struct { 
#define cpuhp_lock_acquire()      lock_map_acquire(&cpu_hotplug.dep_map)

#define cpuhp_lock_release()      lock_map_release(&cpu_hotplug.dep_map)



void cpu_hotplug_mutex_held(void)

{

	lockdep_assert_held(&cpu_hotplug.lock);

}

EXPORT_SYMBOL(cpu_hotplug_mutex_held);



void get_online_cpus(void)

{

kernel/cpuset.c

+19 −14
Original line number Diff line number Diff line
@@ -806,16 +806,15 @@ done: 
 * '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_unlocked(void)

{

	struct sched_domain_attr *attr;

	cpumask_var_t *doms;

	int ndoms;



	cpu_hotplug_mutex_held();

	lockdep_assert_held(&cpuset_mutex);

	get_online_cpus();



	/*

	 * We have raced with CPU hotplug. Don't do anything to avoid
@@ -823,27 +822,27 @@ 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_unlocked(void)

{

}

#endif /* CONFIG_SMP */



void rebuild_sched_domains(void)

{

	get_online_cpus();

	mutex_lock(&cpuset_mutex);

	rebuild_sched_domains_locked();

	rebuild_sched_domains_unlocked();

	mutex_unlock(&cpuset_mutex);

	put_online_cpus();

}



/**
@@ -875,7 +874,6 @@ static void update_tasks_cpumask(struct cpuset *cs) 
 *

 * On legacy hierachy, effective_cpus will be the same with cpu_allowed.

 *

 * Called with cpuset_mutex held

 */

static void update_cpumasks_hier(struct cpuset *cs, struct cpumask *new_cpus)

{
@@ -930,7 +928,7 @@ 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_unlocked();

}



/**
@@ -1289,7 +1287,7 @@ 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_unlocked();

	}



	return 0;
@@ -1320,7 +1318,6 @@ static void update_tasks_flags(struct cpuset *cs) 
 * cs:		the cpuset to update

 * turning_on: 	whether the flag is being set or cleared

 *

 * Call with cpuset_mutex held.

 */



static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
@@ -1355,7 +1352,7 @@ 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_unlocked();



	if (spread_flag_changed)

		update_tasks_flags(cs);
@@ -1620,6 +1617,7 @@ static int cpuset_write_u64(struct cgroup_subsys_state *css, struct cftype *cft, 
	cpuset_filetype_t type = cft->private;

	int retval = 0;



	get_online_cpus();

	mutex_lock(&cpuset_mutex);

	if (!is_cpuset_online(cs)) {

		retval = -ENODEV;
@@ -1657,6 +1655,7 @@ static int cpuset_write_u64(struct cgroup_subsys_state *css, struct cftype *cft, 
	}

out_unlock:

	mutex_unlock(&cpuset_mutex);

	put_online_cpus();

	return retval;

}
@@ -1667,6 +1666,7 @@ static int cpuset_write_s64(struct cgroup_subsys_state *css, struct cftype *cft, 
	cpuset_filetype_t type = cft->private;

	int retval = -ENODEV;



	get_online_cpus();

	mutex_lock(&cpuset_mutex);

	if (!is_cpuset_online(cs))

		goto out_unlock;
@@ -1681,6 +1681,7 @@ static int cpuset_write_s64(struct cgroup_subsys_state *css, struct cftype *cft, 
	}

out_unlock:

	mutex_unlock(&cpuset_mutex);

	put_online_cpus();

	return retval;

}
@@ -1719,6 +1720,7 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of, 
	kernfs_break_active_protection(of->kn);

	flush_work(&cpuset_hotplug_work);



	get_online_cpus();

	mutex_lock(&cpuset_mutex);

	if (!is_cpuset_online(cs))

		goto out_unlock;
@@ -1744,6 +1746,7 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of, 
	free_trial_cpuset(trialcs);

out_unlock:

	mutex_unlock(&cpuset_mutex);

	put_online_cpus();

	kernfs_unbreak_active_protection(of->kn);

	css_put(&cs->css);

	flush_workqueue(cpuset_migrate_mm_wq);
@@ -2049,13 +2052,14 @@ out_unlock: 
/*

 * 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_unlocked().

 */



static void cpuset_css_offline(struct cgroup_subsys_state *css)

{

	struct cpuset *cs = css_cs(css);



	get_online_cpus();

	mutex_lock(&cpuset_mutex);



	if (is_sched_load_balance(cs))
@@ -2065,6 +2069,7 @@ static void cpuset_css_offline(struct cgroup_subsys_state *css) 
	clear_bit(CS_ONLINE, &cs->flags);



	mutex_unlock(&cpuset_mutex);

	put_online_cpus();

}



static void cpuset_css_free(struct cgroup_subsys_state *css)