linux-kernel - Re: [PATCH V2 7/8] nvme: use blk_mq_queue_tag_inflight

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Date:   Wed, 27 Mar 2019 10:45:33 +0800
From:   "jianchao.wang" <jianchao.w.wang@...cle.com>
To:     Keith Busch <kbusch@...nel.org>
Cc:     Jens Axboe <axboe@...nel.dk>,
        linux-block <linux-block@...r.kernel.org>,
        James Smart <jsmart2021@...il.com>,
        Bart Van Assche <bvanassche@....org>,
        Ming Lei <tom.leiming@...il.com>,
        Josef Bacik <josef@...icpanda.com>,
        linux-nvme <linux-nvme@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Busch, Keith" <keith.busch@...el.com>,
        Hannes Reinecke <hare@...e.de>,
        Johannes Thumshirn <jthumshirn@...e.de>,
        Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>
Subject: Re: [PATCH V2 7/8] nvme: use blk_mq_queue_tag_inflight_iter

Hi Keith

On 3/27/19 10:33 AM, Keith Busch wrote:
> On Wed, Mar 27, 2019 at 10:27:57AM +0800, jianchao.wang wrote:
>> As the comment above, the stable request maybe something that has been freed due to following case,
>> 1. a hctx->fq.flush_rq of dead request_queue that shares the same tagset
>> 2. a removed io scheduler's sched request
>> and this freed request could be allocated by others which may change the field of request->state.
> 
> You're not explaing how that request->state is changed. I understand the
> request can be reallocated, but what is changing its state?
> 

Sorry for my bad description, and lead to the misunderstand.
The _free_ below means,

1. a hctx->fq.flush_rq of dead request_queue that shares the same tagset
   The whole request_queue is cleaned up and freed, so the hctx->fq.flush is freed back to a slab

2. a removed io scheduler's sched request
   The io scheduled is detached and all of the structures are freed, including the pages where sched
   requests locates.

So the pointers in tags->rqs[] may point to memory that is not used as a blk layer request.


Thanks
Jianchao