linux-kernel - Re: [PATCH V1] block: Fix null pointer dereference issue on struct io

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Date:   Mon, 22 May 2023 11:49:32 +0530
From:   Pradeep Pragallapati <quic_pragalla@...cinc.com>
To:     Yu Kuai <yukuai1@...weicloud.com>, <axboe@...nel.dk>
CC:     <linux-block@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        "yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH V1] block: Fix null pointer dereference issue on struct
 io_cq


On 5/18/2023 6:14 PM, Yu Kuai wrote:
> Hi,
>
> 在 2023/05/18 20:16, Yu Kuai 写道:
>
>> @@ -173,18 +171,17 @@ void ioc_clear_queue(struct request_queue *q)
>>   {
>>          LIST_HEAD(icq_list);
>>
>> +       rcu_read_lock();
>
> Sorry that I realized this is still not enough, following list_empty()
> and list_entry() can still concurrent with list_del(). Please try the
> following patch:
sure will try and update the results.
>> spin_lock_irq(&q->queue_lock);
>>          list_splice_init(&q->icq_list, &icq_list);
>>          spin_unlock_irq(&q->queue_lock);
>>
>> -       rcu_read_lock();
>>          while (!list_empty(&icq_list)) {
>>                  struct io_cq *icq =
>>                          list_entry(icq_list.next, struct io_cq, 
>> q_node);
>>
>>                  spin_lock_irq(&icq->ioc->lock);
>> -               if (!(icq->flags & ICQ_DESTROYED))
>> -                       ioc_destroy_icq(icq);
>> +               ioc_destroy_icq(icq);
>>                  spin_unlock_irq(&icq->ioc->lock);
>>          }
>>          rcu_read_unlock();
>>
>> .
>>
>
> diff --git a/block/blk-ioc.c b/block/blk-ioc.c
> index 63fc02042408..47684d1e9006 100644
> --- a/block/blk-ioc.c
> +++ b/block/blk-ioc.c
> @@ -78,6 +78,9 @@ static void ioc_destroy_icq(struct io_cq *icq)
>
>         lockdep_assert_held(&ioc->lock);
>
> +       if (icq->flags & ICQ_DESTROYED)
> +               return;
> +
>         radix_tree_delete(&ioc->icq_tree, icq->q->id);
>         hlist_del_init(&icq->ioc_node);
>         list_del_init(&icq->q_node);
> @@ -128,12 +131,7 @@ static void ioc_release_fn(struct work_struct *work)
>                         spin_lock(&q->queue_lock);
>                         spin_lock(&ioc->lock);
>
> -                       /*
> -                        * The icq may have been destroyed when the 
> ioc lock
> -                        * was released.
> -                        */
> -                       if (!(icq->flags & ICQ_DESTROYED))
> -                               ioc_destroy_icq(icq);
> +                       ioc_destroy_icq(icq);
>
>                         spin_unlock(&q->queue_lock);
>                         rcu_read_unlock();
> @@ -175,19 +173,16 @@ void ioc_clear_queue(struct request_queue *q)
>
>         spin_lock_irq(&q->queue_lock);
>         list_splice_init(&q->icq_list, &icq_list);
> -       spin_unlock_irq(&q->queue_lock);
>
> -       rcu_read_lock();
>         while (!list_empty(&icq_list)) {
>                 struct io_cq *icq =
>                         list_entry(icq_list.next, struct io_cq, q_node);
>
>                 spin_lock_irq(&icq->ioc->lock);
> -               if (!(icq->flags & ICQ_DESTROYED))
> -                       ioc_destroy_icq(icq);
> +               ioc_destroy_icq(icq);
>                 spin_unlock_irq(&icq->ioc->lock);
>         }
> -       rcu_read_unlock();
> +       spin_unlock_irq(&q->queue_lock);
>  }
>  #else /* CONFIG_BLK_ICQ */
>  static inline void ioc_exit_icqs(struct io_context *ioc)
>