Re: [PATCH v4] blk-mq: Fix race conditions in request timeout handling

["jianchao.wang" <jianchao.w.wang@oracle.com>]

Hi Bart

On 04/10/2018 09:34 AM, Bart Van Assche wrote:
> If a completion occurs after blk_mq_rq_timed_out() has reset
> rq->aborted_gstate and the request is again in flight when the timeout
> expires then a request will be completed twice: a first time by the
> timeout handler and a second time when the regular completion occurs

Would you please detail more here about why the request could be completed twice ?

Is it the scenario you described as below in https://marc.info/?l=linux-block&m=151796816127318

The following race can occur between the code that resets the timer
and completion handling:
- The code that handles BLK_EH_RESET_TIMER resets aborted_gstate.
- A completion occurs and blk_mq_complete_request() calls
  __blk_mq_complete_request().
- The timeout code calls blk_add_timer() and that function sets the
  request deadline and adjusts the timer.
- __blk_mq_complete_request() frees the request tag.
- The timer fires and the timeout handler gets called for a freed
  request.
If yes, how does the timeout handler get the freed request when the tag has been freed ?

Thanks
Jianchao