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cgroup/cpuset: remove circular dependency deadlock

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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: Prateek Sood <prsood@codeaurora.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
This commit is contained in:
Prateek Sood
2017-11-15 19:50:14 +05:30
committed by Tejun Heo
parent 4fbd8d194f
commit aa24163b2e
1 changed files with 30 additions and 23 deletions
Download Patch File Download Diff File Expand all files Collapse all files
kernel/cgroup/cpuset.c
+30 -23
View File
@@ -812,6 +812,18 @@ done:
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 @@ 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_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 @@ 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_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)