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

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Date:   Tue, 30 May 2023 18:45:42 +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

Hi,

On 5/22/2023 11:49 AM, Pradeep Pragallapati wrote:
>
> 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.


At least for 80+hrs of testing, i didn't see the issue reproduced. seems 
like it is helping my case.

>>> 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)
>>