linux-kernel - Re: mkfs.f2fs gets stuck with "blk_update

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Date:	Fri, 5 Apr 2013 16:57:01 +0900
From:	Namjae Jeon <linkinjeon@...il.com>
To:	Max Filippov <jcmvbkbc@...il.com>
Cc:	Shaohua Li <shli@...nel.org>, LKML <linux-kernel@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>,
	Jaegeuk Kim <jaegeuk.kim@...sung.com>,
	linux-f2fs-devel@...ts.sourceforge.net, slava@...eyko.com
Subject: Re: mkfs.f2fs gets stuck with "blk_update_request: bio idx 0 >= vcnt
 0" on 3.8

Hi. Max.

I have a question.
Your mmc host driver set to host->max_discard_to by some value instead
of not zero ?

Thanks.

2013/4/5, Max Filippov <jcmvbkbc@...il.com>:
> On Fri, Apr 5, 2013 at 5:53 AM, Shaohua Li <shli@...nel.org> wrote:
>> On Thu, Apr 04, 2013 at 06:00:18AM +0400, Max Filippov wrote:
>
> [...]
>
>>> the commit 0cfbcafcae8b7364b5fa96c2b26ccde7a3a296a9 'block: add plug
>>> for blkdev_issue_discard'
>>> have added merge opportunity for DISCARD requests. When I do
>>> mkfs.f2fs on a 5G partition (0xad8000 sectors) it submits two bios,
>>> one for 0x7fe000 sectors (0xffc00000 bytes) and another for
>>> 0x2da000 sectors (0x5b400000 bytes). Prior to that commit these
>>> bios weren't merged into one request. Now the second bio gets
>>> merged with the first, but the request's __data_len field is unsigned
>>> int
>>> and it gets wrapped to 0x5b000000 bytes instead of 0x15b000000
>>> in the bio_attempt_back_merge. Later this reduced size is passed to
>>> the blk_update_request causing KERN_ERR and not completed
>>> request. Reverting this commit fixes mkfs.f2fs for me.
>>
>> A workaround is setting limits.max_discard_sectors to a smaller value.
>
> I'm not sure:
> 1) in my case max_discard_sectors is 0x7fe000 (0xffc00000 bytes,
>     which still fits into 32 bits) and
> 2) this parameter will only change size of individual discard requests for
>     the discarded range, but as long as these requests are done inside
>     the plug they will be merged anyway with an overflow if we try
>     to discard more than 4G at once.
>
>> So the question is why __data_len isn't sector based? Since disk is
>> sector
>> based, is there any disk finishing IO in byte granularity? Maybe Jens can
>> answer.
>
> --
> Thanks.
> -- Max
> --
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