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

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Hi Bart

Thanks for your kindly response.

On 04/10/2018 09:01 PM, Bart Van Assche wrote:
> On Tue, 2018-04-10 at 15:59 +0800, jianchao.wang wrote:
>> If yes, how does the timeout handler get the freed request when the tag has been freed ?
> 
> Hello Jianchao,
> 
> Have you noticed that the timeout handler does not check whether or not the request
> tag is freed? Additionally, I don't think it would be possible to add such a check
> to the timeout code without introducing a new race condition.

Doesn't blk_mq_queue_tag_busy_iter only iterate the tags that has been allocated/set ?
When the request is freed, the tag will be cleared through blk_mq_put_tag->sbitmap_queue_clear
Do I miss something else ?

Thanks
Jianchao

> 
> 



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