linux-kernel - Re: [PATCH 1/6] blk-mq: protect completion path with RCU

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Date:   Thu, 14 Dec 2017 10:09:42 +0800
From:   "jianchao.wang" <jianchao.w.wang@...cle.com>
To:     Tejun Heo <tj@...nel.org>
Cc:     axboe@...nel.dk, linux-kernel@...r.kernel.org, oleg@...hat.com,
        peterz@...radead.org, kernel-team@...com, osandov@...com,
        linux-block@...r.kernel.org, hch@....de
Subject: Re: [PATCH 1/6] blk-mq: protect completion path with RCU



On 12/14/2017 12:13 AM, Tejun Heo wrote:
> Hello,
> 
> On Wed, Dec 13, 2017 at 11:30:48AM +0800, jianchao.wang wrote:
>>> +	} else {
>>> +		srcu_idx = srcu_read_lock(hctx->queue_rq_srcu);
>>> +		if (!blk_mark_rq_complete(rq))
>>> +			__blk_mq_complete_request(rq);
>>> +		srcu_read_unlock(hctx->queue_rq_srcu, srcu_idx);
>>
>> The __blk_mq_complete_request() could be executed in irq context. There should not be any 
>> sleeping operations in it. If just synchronize with the timeout path to ensure the aborted_gstate
>> to be seen, only rcu is needed here ,as well as the blk_mq_timeout_work.
> 
> Sure, but it's just a lot cleaner to use the same to protect both
> issue and completion; otherwise, whoever who wants to synchronize
> against them have to do awkward double rcu locking.
> 
It's fair. Thanks for your detailed response. That's really appreciated.
> Thanks.
>