linux-kernel - Re: [PATCH v2] loop: avoid EAGAIN, if offset or block

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Message-ID: <baaf9725-09b4-3f2d-1408-ead415f5c20d@acm.org>
Date:   Mon, 25 Nov 2019 11:41:49 -0800
From:   Bart Van Assche <bvanassche@....org>
To:     Jaegeuk Kim <jaegeuk@...nel.org>
Cc:     linux-kernel@...r.kernel.org,
        linux-f2fs-devel@...ts.sourceforge.net, stable@...r.kernel.org,
        Jens Axboe <axboe@...nel.dk>, linux-block@...r.kernel.org
Subject: Re: [PATCH v2] loop: avoid EAGAIN, if offset or block_size are
 changed

On 11/25/19 11:22 AM, Jaegeuk Kim wrote:
> On 11/25, Bart Van Assche wrote:
>> Thank you for the additional and very helpful clarification. Can you have a look at the (totally untested) patch below? I prefer that version because it prevents concurrent processing of requests and syncing/killing the bdev.
> 
> Yeah, I thought this was much cleaner way, but wasn't sure it could be doable
> to sync|kill block device after freezing the queue. Is it okay?

Hi Jaegeuk,

That patch was based on an incorrect interpretation of the meaning of 
lo_device. After having taken another loop at the block driver, I don't 
think that calling sync after freezing the queue is OK. How about using 
the following call sequence:
* sync_blockdev()
* blk_mq_freeze_queue()
* kill_bdev()

Thanks,

Bart.