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: Prateek Sood <prsood@codeaurora.org>
Signed-off-by: Tejun Heo <tj@kernel.org>
hifive-unleashed-5.1
Prateek Sood
Tejun Heo
parent
4fbd8d194f
commit
aa24163b2e
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@ -812,6 +812,18 @@ done:
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return ndoms;
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}
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static void cpuset_sched_change_begin(void)
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{
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cpus_read_lock();
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mutex_lock(&cpuset_mutex);
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}
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static void cpuset_sched_change_end(void)
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{
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mutex_unlock(&cpuset_mutex);
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cpus_read_unlock();
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}
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/*
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* Rebuild scheduler domains.
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*
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@ -821,16 +833,14 @@ done:
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* 'cpus' is removed, then call this routine to rebuild the
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* scheduler's dynamic sched domains.
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*
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* Call with cpuset_mutex held. Takes get_online_cpus().
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*/
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static void rebuild_sched_domains_locked(void)
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static void rebuild_sched_domains_cpuslocked(void)
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{
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struct sched_domain_attr *attr;
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cpumask_var_t *doms;
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int ndoms;
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lockdep_assert_held(&cpuset_mutex);
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get_online_cpus();
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/*
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* We have raced with CPU hotplug. Don't do anything to avoid
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@ -838,27 +848,25 @@ static void rebuild_sched_domains_locked(void)
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* Anyways, hotplug work item will rebuild sched domains.
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*/
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if (!cpumask_equal(top_cpuset.effective_cpus, cpu_active_mask))
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goto out;
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return;
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/* Generate domain masks and attrs */
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ndoms = generate_sched_domains(&doms, &attr);
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/* Have scheduler rebuild the domains */
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partition_sched_domains(ndoms, doms, attr);
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out:
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put_online_cpus();
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}
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#else /* !CONFIG_SMP */
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static void rebuild_sched_domains_locked(void)
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static void rebuild_sched_domains_cpuslocked(void)
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{
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}
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#endif /* CONFIG_SMP */
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void rebuild_sched_domains(void)
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{
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mutex_lock(&cpuset_mutex);
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rebuild_sched_domains_locked();
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mutex_unlock(&cpuset_mutex);
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cpuset_sched_change_begin();
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rebuild_sched_domains_cpuslocked();
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cpuset_sched_change_end();
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}
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/**
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@ -944,7 +952,7 @@ static void update_cpumasks_hier(struct cpuset *cs, struct cpumask *new_cpus)
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rcu_read_unlock();
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if (need_rebuild_sched_domains)
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rebuild_sched_domains_locked();
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rebuild_sched_domains_cpuslocked();
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}
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/**
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@ -1276,7 +1284,7 @@ static int update_relax_domain_level(struct cpuset *cs, s64 val)
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cs->relax_domain_level = val;
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if (!cpumask_empty(cs->cpus_allowed) &&
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is_sched_load_balance(cs))
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rebuild_sched_domains_locked();
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rebuild_sched_domains_cpuslocked();
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}
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return 0;
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@ -1309,7 +1317,6 @@ static void update_tasks_flags(struct cpuset *cs)
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*
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* Call with cpuset_mutex held.
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*/
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static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
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int turning_on)
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{
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@ -1342,7 +1349,7 @@ static int update_flag(cpuset_flagbits_t bit, struct cpuset *cs,
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spin_unlock_irq(&callback_lock);
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if (!cpumask_empty(trialcs->cpus_allowed) && balance_flag_changed)
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rebuild_sched_domains_locked();
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rebuild_sched_domains_cpuslocked();
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if (spread_flag_changed)
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update_tasks_flags(cs);
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@ -1610,7 +1617,7 @@ static int cpuset_write_u64(struct cgroup_subsys_state *css, struct cftype *cft,
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cpuset_filetype_t type = cft->private;
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int retval = 0;
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mutex_lock(&cpuset_mutex);
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cpuset_sched_change_begin();
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if (!is_cpuset_online(cs)) {
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retval = -ENODEV;
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goto out_unlock;
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@ -1646,7 +1653,7 @@ static int cpuset_write_u64(struct cgroup_subsys_state *css, struct cftype *cft,
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break;
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}
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out_unlock:
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mutex_unlock(&cpuset_mutex);
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cpuset_sched_change_end();
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return retval;
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}
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@ -1657,7 +1664,7 @@ static int cpuset_write_s64(struct cgroup_subsys_state *css, struct cftype *cft,
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cpuset_filetype_t type = cft->private;
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int retval = -ENODEV;
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mutex_lock(&cpuset_mutex);
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cpuset_sched_change_begin();
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if (!is_cpuset_online(cs))
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goto out_unlock;
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@ -1670,7 +1677,7 @@ static int cpuset_write_s64(struct cgroup_subsys_state *css, struct cftype *cft,
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break;
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}
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out_unlock:
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mutex_unlock(&cpuset_mutex);
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cpuset_sched_change_end();
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return retval;
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}
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@ -1709,7 +1716,7 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
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kernfs_break_active_protection(of->kn);
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flush_work(&cpuset_hotplug_work);
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mutex_lock(&cpuset_mutex);
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cpuset_sched_change_begin();
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if (!is_cpuset_online(cs))
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goto out_unlock;
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@ -1733,7 +1740,7 @@ static ssize_t cpuset_write_resmask(struct kernfs_open_file *of,
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free_trial_cpuset(trialcs);
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out_unlock:
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mutex_unlock(&cpuset_mutex);
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cpuset_sched_change_end();
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kernfs_unbreak_active_protection(of->kn);
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css_put(&cs->css);
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flush_workqueue(cpuset_migrate_mm_wq);
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@ -2034,14 +2041,14 @@ out_unlock:
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/*
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* If the cpuset being removed has its flag 'sched_load_balance'
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* enabled, then simulate turning sched_load_balance off, which
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* will call rebuild_sched_domains_locked().
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* will call rebuild_sched_domains_cpuslocked().
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*/
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static void cpuset_css_offline(struct cgroup_subsys_state *css)
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{
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struct cpuset *cs = css_cs(css);
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mutex_lock(&cpuset_mutex);
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cpuset_sched_change_begin();
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if (is_sched_load_balance(cs))
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update_flag(CS_SCHED_LOAD_BALANCE, cs, 0);
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@ -2049,7 +2056,7 @@ static void cpuset_css_offline(struct cgroup_subsys_state *css)
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cpuset_dec();
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clear_bit(CS_ONLINE, &cs->flags);
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mutex_unlock(&cpuset_mutex);
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cpuset_sched_change_end();
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}
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static void cpuset_css_free(struct cgroup_subsys_state *css)
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