Re: [PATCH 1/2] virtio-blk: Fix hot-unplug race in remove method

[Asias He <asias@redhat.com>]

On 05/03/2012 01:02 PM, Sasha Levin wrote:
> On Thu, May 3, 2012 at 4:19 AM, Asias He<asias@redhat.com>  wrote:
>> @@ -190,6 +194,7 @@ static void do_virtblk_request(struct request_queue *q)
>>
>>         while ((req = blk_peek_request(q)) != NULL) {
>>                 BUG_ON(req->nr_phys_segments + 2>  vblk->sg_elems);
>> +               vblk->req_in_flight++;
>>
>>                 /* If this request fails, stop queue and wait for something to
>>                    finish to restart it. */
>
> This is being increased before we know if the request will actually be
> sent, so if do_req() fails afterwards, req_in_flight would be
> increased but the request will never be sent.
>
> Which means we won't be able to unplug the device ever.

Yes, you are right. This introduces another race. I could do 
vblk->req_in_flight++ right after blk_start_request(req) to avoid this 
race.

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-- 
Asias