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Subject[PATCH 4.14 29/45] cgroup/cpuset: remove circular dependency deadlock
Date
4.14-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Prateek Sood <prsood@codeaurora.org>

commit aa24163b2ee5c92120e32e99b5a93143a0f4258e upstream.

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>
Signed-off-by: Amit Pundir <amit.pundir@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
kernel/cgroup/cpuset.c | 53 +++++++++++++++++++++++++++----------------------
1 file changed, 30 insertions(+), 23 deletions(-)

--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -817,6 +817,18 @@ 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.
*
@@ -826,16 +838,14 @@ 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
@@ -843,27 +853,25 @@ static void rebuild_sched_domains_locked
* 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();
}

/**
@@ -949,7 +957,7 @@ static void update_cpumasks_hier(struct
rcu_read_unlock();

if (need_rebuild_sched_domains)
- rebuild_sched_domains_locked();
+ rebuild_sched_domains_cpuslocked();
}

/**
@@ -1281,7 +1289,7 @@ static int update_relax_domain_level(str
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;
@@ -1314,7 +1322,6 @@ static void update_tasks_flags(struct cp
*
* Call with cpuset_mutex held.
*/
-
static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
int turning_on)
{
@@ -1347,7 +1354,7 @@ static int update_flag(cpuset_flagbits_t
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);
@@ -1615,7 +1622,7 @@ static int cpuset_write_u64(struct cgrou
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;
@@ -1651,7 +1658,7 @@ static int cpuset_write_u64(struct cgrou
break;
}
out_unlock:
- mutex_unlock(&cpuset_mutex);
+ cpuset_sched_change_end();
return retval;
}

@@ -1662,7 +1669,7 @@ static int cpuset_write_s64(struct cgrou
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;

@@ -1675,7 +1682,7 @@ static int cpuset_write_s64(struct cgrou
break;
}
out_unlock:
- mutex_unlock(&cpuset_mutex);
+ cpuset_sched_change_end();
return retval;
}

@@ -1714,7 +1721,7 @@ static ssize_t cpuset_write_resmask(stru
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;

@@ -1738,7 +1745,7 @@ static ssize_t cpuset_write_resmask(stru

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);
@@ -2039,14 +2046,14 @@ 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);
@@ -2054,7 +2061,7 @@ static void cpuset_css_offline(struct cg
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)

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