From: Zhaoyang Huang zhaoyang.huang@unisoc.com
[ Upstream commit 8f91efd870ea5d8bc10b0fcc9740db51cd4c0c83 ]
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") Co-developed-by: ziwei.dai ziwei.dai@unisoc.com Signed-off-by: ziwei.dai ziwei.dai@unisoc.com Co-developed-by: ke.wang ke.wang@unisoc.com Signed-off-by: ke.wang ke.wang@unisoc.com Signed-off-by: Zhaoyang Huang zhaoyang.huang@unisoc.com Signed-off-by: Peter Zijlstra (Intel) peterz@infradead.org Reviewed-by: Suren Baghdasaryan surenb@google.com Acked-by: Johannes Weiner hannes@cmpxchg.org Link: https://lkml.kernel.org/r/1623371374-15664-1-git-send-email-huangzhaoyang@gm... Signed-off-by: Sasha Levin sashal@kernel.org --- 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 cc25a3cff41f..58b36d17a09a 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 + * Stop kthread '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);