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From:   Zhaoyang Huang <huangzhaoyang@gmail.com>
Date:   Tue, 18 May 2021 10:15:21 +0800
Message-ID: <CAGWkznFGmQFieMe6=-APBG=ZAYdpWcc27o+W0s=4ZAF5Pzkvjg@mail.gmail.com>
Subject: Re: [PATCH v2] psi: fix race between psi_trigger_create and psimon
To:     Johannes Weiner <hannes@cmpxchg.org>,
        Suren Baghdasaryan <surenb@google.com>,
        Zhaoyang Huang <zhaoyang.huang@unisoc.com>,
        Ziwei Dai <ziwei.dai@unisoc.com>, Ke Wang <ke.wang@unisoc.com>,
        LKML <linux-kernel@vger.kernel.org>
Cc:     Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Juri Lelli <juri.lelli@redhat.com>,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        Steven Rostedt <rostedt@goodmis.org>,
        Ben Segall <bsegall@google.com>, Mel Gorman <mgorman@suse.de>,
        Daniel Bristot de Oliveira <bristot@redhat.com>
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On Tue, May 18, 2021 at 10:11 AM Huangzhaoyang <huangzhaoyang@gmail.com> wrote:
>
> From: Zhaoyang Huang <zhaoyang.huang@unisoc.com>
>
> 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. It is not necessary to reinit
> resource of psi_system when psi_trigger_create.
>
> 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
>
> Signed-off-by: ziwei.dai <ziwei.dai@unisoc.com>
> Signed-off-by: ke.wang <ke.wang@unisoc.com>
> Signed-off-by: Zhaoyang Huang <zhaoyang.huang@unisoc.com>
> +++
> v2: change del_timer_sync to del_timer in psi_trigger_destroy
> +++
> ---
>  kernel/sched/psi.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
> index cc25a3c..fe29022 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);
>  }
>
> @@ -1157,7 +1161,6 @@ 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);
> @@ -1233,7 +1236,7 @@ static void psi_trigger_destroy(struct kref *ref)
>                  * But it might have been already scheduled before
>                  * that - deschedule it cleanly before destroying it.
>                  */
> -               del_timer_sync(&group->poll_timer);
> +               del_timer(&group->poll_timer);
>                 kthread_stop(task_to_destroy);
>         }
>         kfree(t);
> --
> 1.9.1
>