linux-kernel - Re: [PATCH] null_blk: allow teardown on request timeout

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Message-ID: <52913ebc-5f01-bff4-9b2d-2ee9caf4719d@nvidia.com>
Date:   Mon, 17 Oct 2022 10:04:26 +0000
From:   Chaitanya Kulkarni <chaitanyak@...dia.com>
To:     Ming Lei <ming.lei@...hat.com>
CC:     "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "axboe@...nel.dk" <axboe@...nel.dk>,
        "damien.lemoal@...nsource.wdc.com" <damien.lemoal@...nsource.wdc.com>,
        "johannes.thumshirn@....com" <johannes.thumshirn@....com>,
        "bvanassche@....org" <bvanassche@....org>,
        "shinichiro.kawasaki@....com" <shinichiro.kawasaki@....com>,
        "vincent.fu@...sung.com" <vincent.fu@...sung.com>,
        "yukuai3@...wei.com" <yukuai3@...wei.com>
Subject: Re: [PATCH] null_blk: allow teardown on request timeout

On 10/17/22 02:50, Ming Lei wrote:
> On Mon, Oct 17, 2022 at 09:30:47AM +0000, Chaitanya Kulkarni wrote:
>>
>>>> +	/*
>>>> +	 * Unblock any pending dispatch I/Os before we destroy the device.
>>>> +	 * From null_destroy_dev()->del_gendisk() will set GD_DEAD flag
>>>> +	 * causing any new I/O from __bio_queue_enter() to fail with -ENODEV.
>>>> +	 */
>>>> +	blk_mq_unquiesce_queue(nullb->q);
>>>> +
>>>> +	null_destroy_dev(nullb);
>>>
>>> destroying device is never good cleanup for handling timeout/abort, and it
>>> should have been the last straw any time.
>>>
>>
>> That is exactly why I've added the rq_abort_limit, so until the limit
>> is not reached null_abort_work() will not get scheduled and device is
>> not destroyed.
> 
> I meant destroying device should only be done iff the normal abort handler
> can't recover the device, however, your patch simply destroys device
> without running any abort handling.
> 

I did not understand your comment, can you please elaborate on exactly
where and which abort handlers needs to be called in this patch before
null_destroy_nullb() ?

the objective of this patch it to simulate the teardown scenario
from timeout handler so it can get tested on regular basis with
null_blk ...

-ck