From: Zhaoyang Huang <[email protected]>
Race detected between psi_trigger_destroy/create as shown below, which
cause panic by accessing invalid psi_system->poll_wait->wait_queue_entry
and psi_system->poll_timer->entry->next. Under this modification, the
race window is removed by initialising poll_wait and poll_timer in
group_init which are executed only once at beginning.
psi_trigger_destroy psi_trigger_create
mutex_lock(trigger_lock);
rcu_assign_pointer(poll_task, NULL);
mutex_unlock(trigger_lock);
mutex_lock(trigger_lock);
if (!rcu_access_pointer(group->poll_task)) {
timer_setup(poll_timer, poll_timer_fn, 0);
rcu_assign_pointer(poll_task, task);
}
mutex_unlock(trigger_lock);
synchronize_rcu();
del_timer_sync(poll_timer); <-- poll_timer has been reinitialized by
psi_trigger_create
So, trigger_lock/RCU correctly protects destruction of group->poll_task but
misses this race affecting poll_timer and poll_wait.
Fixes: 461daba06bdc ("psi: eliminate kthread_worker from psi trigger
scheduling mechanism")
Signed-off-by: ziwei.dai <[email protected]>
Signed-off-by: ke.wang <[email protected]>
Signed-off-by: Zhaoyang Huang <[email protected]>
---
v2: change del_timer_sync to del_timer in psi_trigger_destroy
v3: remove timer_setup within psi_tirgger_create
protect del_timer by extending the critical section of mutex_lock
v4: amend fix information on comment
v5: delete the poll_timer while assigning the task to NULL
---
---
kernel/sched/psi.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)
diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
index cc25a3c..075501e 100644
--- a/kernel/sched/psi.c
+++ b/kernel/sched/psi.c
@@ -182,6 +182,8 @@ struct psi_group psi_system = {
static void psi_avgs_work(struct work_struct *work);
+static void poll_timer_fn(struct timer_list *t);
+
static void group_init(struct psi_group *group)
{
int cpu;
@@ -201,6 +203,8 @@ static void group_init(struct psi_group *group)
memset(group->polling_total, 0, sizeof(group->polling_total));
group->polling_next_update = ULLONG_MAX;
group->polling_until = 0;
+ init_waitqueue_head(&group->poll_wait);
+ timer_setup(&group->poll_timer, poll_timer_fn, 0);
rcu_assign_pointer(group->poll_task, NULL);
}
@@ -1157,9 +1161,7 @@ struct psi_trigger *psi_trigger_create(struct psi_group *group,
return ERR_CAST(task);
}
atomic_set(&group->poll_wakeup, 0);
- init_waitqueue_head(&group->poll_wait);
wake_up_process(task);
- timer_setup(&group->poll_timer, poll_timer_fn, 0);
rcu_assign_pointer(group->poll_task, task);
}
@@ -1211,6 +1213,7 @@ static void psi_trigger_destroy(struct kref *ref)
group->poll_task,
lockdep_is_held(&group->trigger_lock));
rcu_assign_pointer(group->poll_task, NULL);
+ del_timer(&group->poll_timer);
}
}
@@ -1223,17 +1226,14 @@ static void psi_trigger_destroy(struct kref *ref)
*/
synchronize_rcu();
/*
- * Destroy the kworker after releasing trigger_lock to prevent a
+ * Destroy psimon after releasing trigger_lock to prevent a
* deadlock while waiting for psi_poll_work to acquire trigger_lock
*/
if (task_to_destroy) {
/*
* After the RCU grace period has expired, the worker
* can no longer be found through group->poll_task.
- * But it might have been already scheduled before
- * that - deschedule it cleanly before destroying it.
*/
- del_timer_sync(&group->poll_timer);
kthread_stop(task_to_destroy);
}
kfree(t);
--
1.9.1