linux-kernel - Re: [PATCH] block: fix max discard sectors limit

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Date:	Wed, 24 Apr 2013 13:09:28 +0900
From:	Namjae Jeon <linkinjeon@...il.com>
To:	James Bottomley <jbottomley@...allels.com>
Cc:	"axboe@...nel.dk" <axboe@...nel.dk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Namjae Jeon <namjae.jeon@...sung.com>,
	Vivek Trivedi <t.vivek@...sung.com>,
	Shaohua Li <shli@...nel.org>,
	Kent Overstreet <koverstreet@...gle.com>,
	Tejun Heo <tj@...nel.org>,
	"stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH] block: fix max discard sectors limit

2013/4/23, James Bottomley <jbottomley@...allels.com>:
> On Tue, 2013-04-23 at 22:06 +0900, Namjae Jeon wrote:
>> From: Namjae Jeon <namjae.jeon@...sung.com>
>
> Hey, it's very impolite to send a patch I just gave you as a suggestion
> to fix the issue under your own authorship.
>
> What we need to know is has this been tested ... there's no tested-by
> tags (and there also should really be a reported by).
Sorry James, as I do not have the exact MMC on which the issue is reproduce.
So I just checked for sanity on my MMC - there was no issue.
But for exact issue fix it was mistake to not request for testing.
I will take care of this in future, for pushing such patches.
Thanks.
>
> James
>
>> linux-v3.8-rc1 and later support for plug for blkdev_issue_discard with
>> commit 0cfbcafcae8b7364b5fa96c2b26ccde7a3a296a9
>> (block: add plug for blkdev_issue_discard )
>>
>> For example,
>> 1) DISCARD rq-1 with size size 4GB
>> 2) DISCARD rq-2 with size size 1GB
>>
>> If these 2 discard requests get merged, final request size will be 5GB.
>>
>> In this case, request's __data_len field may overflow as it can store
>> max 4GB(unsigned int).
>>
>> This issue was observed while doing mkfs.f2fs on 5GB SD card:
>> https://lkml.org/lkml/2013/4/1/292
>>
>> Info: sector size = 512
>> Info: total sectors = 11370496 (in 512bytes)
>> Info: zone aligned segment0 blkaddr: 512
>> [  257.789764] blk_update_request: bio idx 0 >= vcnt 0
>>
>> mkfs process gets stuck in D state and I see the following in the dmesg:
>>
>> [  257.789733] __end_that: dev mmcblk0: type=1, flags=122c8081
>> [  257.789764]   sector 4194304, nr/cnr 2981888/4294959104
>> [  257.789764]   bio df3840c0, biotail df3848c0, buffer   (null), len
>> 1526726656
>> [  257.789764] blk_update_request: bio idx 0 >= vcnt 0
>> [  257.794921] request botched: dev mmcblk0: type=1, flags=122c8081
>> [  257.794921]   sector 4194304, nr/cnr 2981888/4294959104
>> [  257.794921]   bio df3840c0, biotail df3848c0, buffer   (null), len
>> 1526726656
>>
>> This patch fixes this issue.
>>
>> Reported-by: Max Filippov <jcmvbkbc@...il.com>
>> Signed-off-by: Namjae Jeon <namjae.jeon@...sung.com>
>> Signed-off-by: Vivek Trivedi <t.vivek@...sung.com>
>> Signed-off-by: James Bottomley <JBottomley@...allels.com>
>> Cc: Shaohua Li <shli@...nel.org>
>> Cc: Kent Overstreet <koverstreet@...gle.com>
>> Cc: Tejun Heo <tj@...nel.org>
>> Cc: Jens Axboe <axboe@...nel.dk>
>> Cc: <stable@...r.kernel.org>
>> ---
>>  include/linux/blkdev.h |    2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
>> index 07aa5f6..ff636bd 100644
>> --- a/include/linux/blkdev.h
>> +++ b/include/linux/blkdev.h
>> @@ -844,7 +844,7 @@ static inline unsigned int
>> blk_queue_get_max_sectors(struct request_queue *q,
>>  						     unsigned int cmd_flags)
>>  {
>>  	if (unlikely(cmd_flags & REQ_DISCARD))
>> -		return q->limits.max_discard_sectors;
>> +		return min(q->limits.max_discard_sectors, UINT_MAX >> 9);
>>
>>  	if (unlikely(cmd_flags & REQ_WRITE_SAME))
>>  		return q->limits.max_write_same_sectors;
>
>
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