linux-kernel - Re: [PATCH 5/5] scsi: libsas: fix a race condition when smp task timeout

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Date:   Wed, 19 Sep 2018 10:49:06 +0800
From:   Jason Yan <yanaijie@...wei.com>
To:     John Garry <john.garry@...wei.com>, <martin.petersen@...cle.com>,
        <jejb@...ux.vnet.ibm.com>
CC:     <linux-scsi@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <zhaohongjiang@...wei.com>, <hare@...e.com>,
        <dan.j.williams@...el.com>, <jthumshirn@...e.de>, <hch@....de>,
        <huangdaode@...ilicon.com>, <chenxiang66@...ilicon.com>,
        <miaoxie@...wei.com>, Ewan Milne <emilne@...hat.com>,
        Tomas Henzl <thenzl@...hat.com>, Linuxarm <linuxarm@...wei.com>
Subject: Re: [PATCH 5/5] scsi: libsas: fix a race condition when smp task
 timeout



On 2018/9/17 17:47, John Garry wrote:
> On 12/09/2018 09:29, Jason Yan wrote:
>> When the lldd is processing the complete sas task in interrupt and set
>> the task stat as SAS_TASK_STATE_DONE, the smp timeout timer is able to
>> be triggered at the same time. And smp_task_timedout() will complete the
>> task wheter the SAS_TASK_STATE_DONE is set or not. Then the sas task may
>> freed before lldd end the interrupt process. Thus a use-after-free will
>> happen.
>>
>> Fix this by calling the complete() only when SAS_TASK_STATE_DONE is not
>> set. And remove the check of the return value of the del_timer().
>>
>
> Hi Jason,
>
> Please mention that once the LLDD sets DONE, it must call task->done(),
> which will call smp_task_done()->complete()
>

OK

>> Reported-by: chenxiang <chenxiang66@...ilicon.com>
>> Signed-off-by: Jason Yan <yanaijie@...wei.com>
>> CC: John Garry <john.garry@...wei.com>
>> CC: Johannes Thumshirn <jthumshirn@...e.de>
>> CC: Ewan Milne <emilne@...hat.com>
>> CC: Christoph Hellwig <hch@....de>
>> CC: Tomas Henzl <thenzl@...hat.com>
>> CC: Dan Williams <dan.j.williams@...el.com>
>> CC: Hannes Reinecke <hare@...e.com>
>> ---
>>  drivers/scsi/libsas/sas_expander.c | 9 ++++-----
>>  1 file changed, 4 insertions(+), 5 deletions(-)
>>
>> diff --git a/drivers/scsi/libsas/sas_expander.c
>> b/drivers/scsi/libsas/sas_expander.c
>> index 52222940d398..0d1f72752ca2 100644
>> --- a/drivers/scsi/libsas/sas_expander.c
>> +++ b/drivers/scsi/libsas/sas_expander.c
>> @@ -48,17 +48,16 @@ static void smp_task_timedout(struct timer_list *t)
>>      unsigned long flags;
>>
>>      spin_lock_irqsave(&task->task_state_lock, flags);
>> -    if (!(task->task_state_flags & SAS_TASK_STATE_DONE))
>> +    if (!(task->task_state_flags & SAS_TASK_STATE_DONE)) {
>>          task->task_state_flags |= SAS_TASK_STATE_ABORTED;
>> +        complete(&task->slow_task->completion);
>
> Nit: for consistency with any other time we use this lock, can we call
> complete() outside the lock? Maybe just use a flag variable for this.
>

Is it necessary to add a variable just for consistency with other places?

>> +    }
>>      spin_unlock_irqrestore(&task->task_state_lock, flags);
>> -
>> -    complete(&task->slow_task->completion);
>>  }
>>
>>  static void smp_task_done(struct sas_task *task)
>>  {
>> -    if (!del_timer(&task->slow_task->timer))
>> -        return;
>> +    del_timer(&task->slow_task->timer);
>>      complete(&task->slow_task->completion);
>>  }
>
> Do we also need this change or similar:
> static int smp_execute_task_sg(struct domain_device *dev,
>      if ((task->task_state_flags & SAS_TASK_STATE_ABORTED)) {
>          SAS_DPRINTK("smp task timed out or aborted\n");
>          i->dft->lldd_abort_task(task);
> -        if (!(task->task_state_flags & SAS_TASK_STATE_DONE)) {
> -            SAS_DPRINTK("SMP task aborted and not done\n");
> -            break;
> -        }
> +        break;
>
> To me, the ABORTED and DONE states are mutually exclusive.
>

This changes the logic a bit. To be safe, maybe we shall do this with 
another patch after some tests.

>>
>>
>
> Thanks,
> John
>
>
>
> .
>