From: Zhaoyang Huang <[email protected]>
Race detected between psimon_new and psimon_old 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_create psimon_new psimon_old
init_waitqueue_head finish_wait
spin_lock(lock_old)
spin_lock_init(lock_new)
wake_up_process(psimon_new)
finish_wait
spin_lock(lock_new)
list_del list_del
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
Thanks! The code looks good to me, just a couple nits below.
On Wed, May 19, 2021 at 6:56 PM Huangzhaoyang <[email protected]> wrote:
>
> From: Zhaoyang Huang <[email protected]>
>
> Race detected between psimon_new and psimon_old 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.
I still think describing this as a race between psi_trigger_create and
psi_trigger_destroy would be better. Description in abstract terms
like "psimon_new" and "psimon_old" is not very clear IMO. Feel free to
borrow from my reply at
https://lore.kernel.org/patchwork/patch/1429498/#1627054, but I won't
object to the current version as well.
>
> psi_trigger_create psimon_new psimon_old
> init_waitqueue_head finish_wait
> spin_lock(lock_old)
> spin_lock_init(lock_new)
> wake_up_process(psimon_new)
>
> finish_wait
> spin_lock(lock_new)
> list_del list_del
>
> 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]>
Reviewed-by: Suren Baghdasaryan <[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
Technically this should read as "Stop kthread" instead of "Destroy psimon".
> * 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
>