+++ /dev/null
-From aa24163b2ee5c92120e32e99b5a93143a0f4258e Mon Sep 17 00:00:00 2001
-From: Prateek Sood <prsood@codeaurora.org>
-Date: Wed, 15 Nov 2017 19:50:14 +0530
-Subject: cgroup/cpuset: remove circular dependency deadlock
-
-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)
projects / thirdparty / kernel / stable-queue.git / commitdiff
