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. After inverting the locking sequence of cpu_hotplug_lock
and cpuset_mutex, cpuset_hotplug_workfn() related functionality can be
done synchronously from the context doing cpu hotplug. For memory hotplug
it still gets queued as a work item.
Signed-off-by: Prateek Sood <prsood@xxxxxxxxxxxxxx>
---
include/linux/cpuset.h | 6 ----
kernel/cgroup/cpuset.c | 94 +++++++++++++++++++++++++++-----------------------
kernel/power/process.c | 2 --
kernel/sched/core.c | 1 -
4 files changed, 50 insertions(+), 53 deletions(-)
diff --git a/include/linux/cpuset.h b/include/linux/cpuset.h
index a1e6a33..e74655d 100644
--- a/include/linux/cpuset.h
+++ b/include/linux/cpuset.h
@@ -51,9 +51,7 @@ static inline void cpuset_dec(void)
extern int cpuset_init(void);
extern void cpuset_init_smp(void);
-extern void cpuset_force_rebuild(void);
extern void cpuset_update_active_cpus(void);
-extern void cpuset_wait_for_hotplug(void);
extern void cpuset_cpus_allowed(struct task_struct *p, struct cpumask *mask);
extern void cpuset_cpus_allowed_fallback(struct task_struct *p);
extern nodemask_t cpuset_mems_allowed(struct task_struct *p);
@@ -166,15 +164,11 @@ static inline void set_mems_allowed(nodemask_t nodemask)
static inline int cpuset_init(void) { return 0; }
static inline void cpuset_init_smp(void) {}
-static inline void cpuset_force_rebuild(void) { }
-
static inline void cpuset_update_active_cpus(void)
{
partition_sched_domains(1, NULL, NULL);
}
-static inline void cpuset_wait_for_hotplug(void) { }
-
static inline void cpuset_cpus_allowed(struct task_struct *p,
struct cpumask *mask)
{
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index 4657e29..ec44aaa 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -817,6 +817,18 @@ static int generate_sched_domains(cpumask_var_t **domains,
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 @@ static int generate_sched_domains(cpumask_var_t **domains,
* '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(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();
}
/**
@@ -949,7 +957,7 @@ 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();
}
/**
@@ -1281,7 +1289,7 @@ 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;
@@ -1314,7 +1322,6 @@ 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)
{
@@ -1347,7 +1354,7 @@ 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);
@@ -1615,7 +1622,7 @@ 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;
@@ -1651,7 +1658,7 @@ 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;
}
@@ -1662,7 +1669,7 @@ 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;
@@ -1675,7 +1682,7 @@ 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;
}
@@ -1714,7 +1721,7 @@ 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;
@@ -1738,7 +1745,7 @@ 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);
@@ -2039,14 +2046,14 @@ static int cpuset_css_online(struct cgroup_subsys_state *css)
/*
* 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 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)
@@ -2275,15 +2282,8 @@ static void cpuset_hotplug_update_tasks(struct cpuset *cs)
mutex_unlock(&cpuset_mutex);
}
-static bool force_rebuild;
-
-void cpuset_force_rebuild(void)
-{
- force_rebuild = true;
-}
-
/**
- * cpuset_hotplug_workfn - handle CPU/memory hotunplug for a cpuset
+ * cpuset_hotplug - handle CPU/memory hotunplug for a cpuset
*
* This function is called after either CPU or memory configuration has
* changed and updates cpuset accordingly. The top_cpuset is always
@@ -2298,7 +2298,7 @@ void cpuset_force_rebuild(void)
* Note that CPU offlining during suspend is ignored. We don't modify
* cpusets across suspend/resume cycles at all.
*/
-static void cpuset_hotplug_workfn(struct work_struct *work)
+static void cpuset_hotplug(bool use_cpu_hp_lock)
{
static cpumask_t new_cpus;
static nodemask_t new_mems;
@@ -2356,25 +2356,31 @@ static void cpuset_hotplug_workfn(struct work_struct *work)
}
/* rebuild sched domains if cpus_allowed has changed */
- if (cpus_updated || force_rebuild) {
- force_rebuild = false;
- rebuild_sched_domains();
+ if (cpus_updated) {
+ if (use_cpu_hp_lock)
+ rebuild_sched_domains();
+ else {
+ /* Acquiring cpu_hotplug_lock is not required.
+ * When cpuset_hotplug() is called in hotplug path,
+ * cpu_hotplug_lock is held by the hotplug context
+ * which is waiting for cpuhp_thread_fun to indicate
+ * completion of callback.
+ */
+ mutex_lock(&cpuset_mutex);
+ rebuild_sched_domains_cpuslocked();
+ mutex_unlock(&cpuset_mutex);
+ }
}
}
-void cpuset_update_active_cpus(void)
+static void cpuset_hotplug_workfn(struct work_struct *work)
{
- /*
- * We're inside cpu hotplug critical region which usually nests
- * inside cgroup synchronization. Bounce actual hotplug processing
- * to a work item to avoid reverse locking order.
- */
- schedule_work(&cpuset_hotplug_work);
+ cpuset_hotplug(true);
}
-void cpuset_wait_for_hotplug(void)
+void cpuset_update_active_cpus(void)
{
- flush_work(&cpuset_hotplug_work);
+ cpuset_hotplug(false);
}
/*
diff --git a/kernel/power/process.c b/kernel/power/process.c
index 50f25cb..28772b405 100644
--- a/kernel/power/process.c
+++ b/kernel/power/process.c
@@ -203,8 +203,6 @@ void thaw_processes(void)
__usermodehelper_set_disable_depth(UMH_FREEZING);
thaw_workqueues();
- cpuset_wait_for_hotplug();
-
read_lock(&tasklist_lock);
for_each_process_thread(g, p) {
/* No other threads should have PF_SUSPEND_TASK set */
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index d17c5da..25b8717 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -5590,7 +5590,6 @@ static void cpuset_cpu_active(void)
* restore the original sched domains by considering the
* cpuset configurations.
*/
- cpuset_force_rebuild();
}
cpuset_update_active_cpus();
}
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