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SubjectRe: [PATCH 5/5] scsi: libsas: fix a race condition when smp task timeout
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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@hisilicon.com>
>> Signed-off-by: Jason Yan <yanaijie@huawei.com>
>> CC: John Garry <john.garry@huawei.com>
>> CC: Johannes Thumshirn <jthumshirn@suse.de>
>> CC: Ewan Milne <emilne@redhat.com>
>> CC: Christoph Hellwig <hch@lst.de>
>> CC: Tomas Henzl <thenzl@redhat.com>
>> CC: Dan Williams <dan.j.williams@intel.com>
>> CC: Hannes Reinecke <hare@suse.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
>
>
>
> .
>

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