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

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Message-ID: <CAMo8BfJOEdZ3OzZUG6fU_sdMzaHCEUkin1cMwzoezbsScby5=A@mail.gmail.com>
Date:	Fri, 5 Apr 2013 19:01:46 +0400
From:	Max Filippov <jcmvbkbc@...il.com>
To:	Namjae Jeon <linkinjeon@...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 Namjae,

On Fri, Apr 5, 2013 at 11:57 AM, Namjae Jeon <linkinjeon@...il.com> wrote:
> Hi. Max.
>
> I have a question.
> Your mmc host driver set to host->max_discard_to by some value instead
> of not zero ?

I believe it's zero, because the only place where I can see it initialized
(sdhci_add_host in the drivers/mmc/host/sdhci.c) is not built in my
configuration.

> 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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