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Subject: Re: [PATCH -next v2 2/2] md/raid5-cache: fix null-ptr-deref in
 r5l_reclaim_thread()
To:     Yu Kuai <yukuai1@huaweicloud.com>, Song Liu <song@kernel.org>
Cc:     xni@redhat.com, logang@deltatee.com, hch@lst.de, shli@fb.com,
        linux-raid@vger.kernel.org, linux-kernel@vger.kernel.org,
        yi.zhang@huawei.com, yangerkun@huawwe.com,
        "yukuai (C)" <yukuai3@huawei.com>
References: <20230628010756.70649-1-yukuai1@huaweicloud.com>
 <20230628010756.70649-3-yukuai1@huaweicloud.com>
 <CAPhsuW500i9LEcSsAchje46b2maKdj4EVaefPtinZfdP+AqELw@mail.gmail.com>
 <e5d746d0-1d42-3d60-450b-2450f24f0915@huaweicloud.com>
From:   Yu Kuai <yukuai1@huaweicloud.com>
Message-ID: <4690dfff-ad72-bf83-7feb-75018712eb17@huaweicloud.com>
Date:   Fri, 7 Jul 2023 17:16:17 +0800
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Hi,

在 2023/07/07 17:06, Yu Kuai 写道:
> Hi,
> 
> 在 2023/07/07 16:52, Song Liu 写道:
>> On Wed, Jun 28, 2023 at 9:08 AM Yu Kuai <yukuai1@huaweicloud.com> wrote:
>>>
>>> From: Yu Kuai <yukuai3@huawei.com>
>>>
>>> r5l_reclaim_thread() already check that 'conf->log' is not NULL in the
>>> beginning, however, r5c_do_reclaim() and r5l_do_reclaim() will
>>> dereference 'conf->log' again, which will cause null-ptr-deref if
>>> 'conf->log' is set to NULL from r5l_exit_log() concurrently.
>>
>> r5l_exit_log() will wait until reclaim_thread() finishes, and then set
>> conf->log to NULL. So this is not a problem, no?

Perhaps you means this order?

r5l_exit_log
  flush_work(&log->disable_writeback_work)
  conf->log = NULL
  md_unregister_thread(&log->reclaim_thread)

I think this is better indeed.

Thanks,
Kuai
> 
> Patch one just revert this, wait until reclaim_thread() then set
> conf->log to NULL will cause deadlock, as I sescribled in patch 0.
> 
> Thanks,
> Kuai
>>
>> Thanks,
>> Song
>>
>>>
>>> Fix this problem by don't dereference 'conf->log' again in
>>> r5c_do_reclaim() and r5c_do_reclaim().
>>>
>>> Fixes: a39f7afde358 ("md/r5cache: write-out phase and reclaim support")
>>> Signed-off-by: Yu Kuai <yukuai3@huawei.com>
>>> ---
>>>   drivers/md/raid5-cache.c | 20 ++++++++------------
>>>   1 file changed, 8 insertions(+), 12 deletions(-)
>>>
>>> diff --git a/drivers/md/raid5-cache.c b/drivers/md/raid5-cache.c
>>> index 083288e36949..ba6fc146d265 100644
>>> --- a/drivers/md/raid5-cache.c
>>> +++ b/drivers/md/raid5-cache.c
>>> @@ -1148,10 +1148,9 @@ static void r5l_run_no_space_stripes(struct 
>>> r5l_log *log)
>>>    * for write through mode, returns log->next_checkpoint
>>>    * for write back, returns log_start of first sh in 
>>> stripe_in_journal_list
>>>    */
>>> -static sector_t r5c_calculate_new_cp(struct r5conf *conf)
>>> +static sector_t r5c_calculate_new_cp(struct r5l_log *log)
>>>   {
>>>          struct stripe_head *sh;
>>> -       struct r5l_log *log = conf->log;
>>>          sector_t new_cp;
>>>          unsigned long flags;
>>>
>>> @@ -1159,12 +1158,12 @@ static sector_t r5c_calculate_new_cp(struct 
>>> r5conf *conf)
>>>                  return log->next_checkpoint;
>>>
>>>          spin_lock_irqsave(&log->stripe_in_journal_lock, flags);
>>> -       if (list_empty(&conf->log->stripe_in_journal_list)) {
>>> +       if (list_empty(&log->stripe_in_journal_list)) {
>>>                  /* all stripes flushed */
>>>                  spin_unlock_irqrestore(&log->stripe_in_journal_lock, 
>>> flags);
>>>                  return log->next_checkpoint;
>>>          }
>>> -       sh = list_first_entry(&conf->log->stripe_in_journal_list,
>>> +       sh = list_first_entry(&log->stripe_in_journal_list,
>>>                                struct stripe_head, r5c);
>>>          new_cp = sh->log_start;
>>>          spin_unlock_irqrestore(&log->stripe_in_journal_lock, flags);
>>> @@ -1173,10 +1172,8 @@ static sector_t r5c_calculate_new_cp(struct 
>>> r5conf *conf)
>>>
>>>   static sector_t r5l_reclaimable_space(struct r5l_log *log)
>>>   {
>>> -       struct r5conf *conf = log->rdev->mddev->private;
>>> -
>>>          return r5l_ring_distance(log, log->last_checkpoint,
>>> -                                r5c_calculate_new_cp(conf));
>>> +                                r5c_calculate_new_cp(log));
>>>   }
>>>
>>>   static void r5l_run_no_mem_stripe(struct r5l_log *log)
>>> @@ -1419,9 +1416,9 @@ void r5c_flush_cache(struct r5conf *conf, int num)
>>>          }
>>>   }
>>>
>>> -static void r5c_do_reclaim(struct r5conf *conf)
>>> +static void r5c_do_reclaim(struct r5l_log *log)
>>>   {
>>> -       struct r5l_log *log = conf->log;
>>> +       struct r5conf *conf = log->rdev->mddev->private;
>>>          struct stripe_head *sh;
>>>          int count = 0;
>>>          unsigned long flags;
>>> @@ -1496,7 +1493,6 @@ static void r5c_do_reclaim(struct r5conf *conf)
>>>
>>>   static void r5l_do_reclaim(struct r5l_log *log)
>>>   {
>>> -       struct r5conf *conf = log->rdev->mddev->private;
>>>          sector_t reclaim_target = xchg(&log->reclaim_target, 0);
>>>          sector_t reclaimable;
>>>          sector_t next_checkpoint;
>>> @@ -1525,7 +1521,7 @@ static void r5l_do_reclaim(struct r5l_log *log)
>>>                                      log->io_list_lock);
>>>          }
>>>
>>> -       next_checkpoint = r5c_calculate_new_cp(conf);
>>> +       next_checkpoint = r5c_calculate_new_cp(log);
>>>          spin_unlock_irq(&log->io_list_lock);
>>>
>>>          if (reclaimable == 0 || !write_super)
>>> @@ -1554,7 +1550,7 @@ static void r5l_reclaim_thread(struct md_thread 
>>> *thread)
>>>
>>>          if (!log)
>>>                  return;
>>> -       r5c_do_reclaim(conf);
>>> +       r5c_do_reclaim(log);
>>>          r5l_do_reclaim(log);
>>>   }
>>>
>>> -- 
>>> 2.39.2
>>>
>> .
>>
> 
> .
>