linux-kernel - Re: [PATCH V2 1/2] blk-mq: init hctx sched after update ctx and hctx mapping

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Message-ID: <96657784-dd95-6ea9-3ffd-25737c534075@oracle.com>
Date:   Mon, 20 Aug 2018 09:29:36 +0800
From:   "jianchao.wang" <jianchao.w.wang@...cle.com>
To:     Ming Lei <tom.leiming@...il.com>
Cc:     Jens Axboe <axboe@...nel.dk>,
        Bart Van Assche <bart.vanassche@....com>,
        Keith Busch <keith.busch@...ux.intel.com>,
        linux-block <linux-block@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 1/2] blk-mq: init hctx sched after update ctx and hctx
 mapping

Hi Ming

On 08/17/2018 05:33 PM, Ming Lei wrote:
>> +               /*
>> +                * elevator_release will put it.
>> +                */
>> +               __module_get(q->elv_type->elevator_owner);
> I understand what elevator_release() frees is the 'ref-counter' got in
> elevator_get(), but who will be the counter-pair of the above  __module_get()?


Sorry for my bad description.

The code path is:

elevator_release
  -> elevator_put(e->type)
    -> module_put(e->elevator_owner)

In normal elevator switch path, elevator_get will hold a reference counter of the
elevator_owner.
In this patch set, the elevator_type is saved directly. To prevent the io scheduler module
is removed, we need to hold a reference of the module.

Thanks
Jianchao