linux-kernel - Re: [PATCH] bio: decrease bi_iter.bi

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Message-ID: <5386B939.5050009@intel.com>
Date:	Thu, 29 May 2014 12:36:09 +0800
From:	Jet Chen <jet.chen@...el.com>
To:	Ming Lei <tom.leiming@...il.com>
CC:	Dongsu Park <dongsu.park@...fitbricks.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Jens Axboe <axboe@...nel.dk>,
	Maurizio Lombardi <mlombard@...hat.com>
Subject: Re: [PATCH] bio: decrease bi_iter.bi_size by len in the fail path

On 05/29/2014 12:13 PM, Ming Lei wrote:
> On Thu, May 29, 2014 at 11:35 AM, Jet Chen <jet.chen@...el.com> wrote:
>> On 05/29/2014 12:59 AM, Ming Lei wrote:
>>> On Wed, May 28, 2014 at 11:42 PM, Ming Lei <tom.leiming@...il.com> wrote:
>>>> Hi Dongsu,
>>>>
>>>> On Wed, May 28, 2014 at 11:09 PM, Dongsu Park
>>>> <dongsu.park@...fitbricks.com> wrote:
>>>>> From: Dongsu Park <dongsu.park@...fitbricks.com>
>>>>>
>>>>> Commit 3979ef4dcf3d1de55a560a3a4016c30a835df44d ("bio-modify-
>>>>> __bio_add_page-to-accept-pages-that-dont-start-a-new-segment-v3")
>>>>> introduced a regression as reported by Jet Chen.
>>>>> That results in a kernel BUG at drivers/block/virtio_blk.c:166.
>>>>>
>>>>> To fix that, bi_iter.bi_size must be decreased by len, before
>>>>> recounting the number of physical segments.
>>>>>
>>>>> Tested on with kernel 3.15.0-rc7-next-20140527 on qemu guest,
>>>>> by running xfstests/ext4/271.
>>>>>
>>>>> Cc: Jens Axboe <axboe@...nel.dk>
>>>>> Cc: Jet Chen <jet.chen@...el.com>
>>>>> Cc: Maurizio Lombardi <mlombard@...hat.com>
>>>>> Signed-off-by: Dongsu Park <dongsu.park@...fitbricks.com>
>>>>> ---
>>>>>   block/bio.c | 1 +
>>>>>   1 file changed, 1 insertion(+)
>>>>>
>>>>> diff --git a/block/bio.c b/block/bio.c
>>>>> index 0443694ccbb4..67d7cba1e5fd 100644
>>>>> --- a/block/bio.c
>>>>> +++ b/block/bio.c
>>>>> @@ -810,6 +810,7 @@ static int __bio_add_page(struct request_queue *q, struct bio *bio, struct page
>>>>>          bvec->bv_len = 0;
>>>>>          bvec->bv_offset = 0;
>>>>>          bio->bi_vcnt--;
>>>>> +       bio->bi_iter.bi_size -= len;
>>>>
>>>> Would you mind explaining why bi_iter.bi_size need to be
>>>> decreased by 'len'? In the failure path, it wasn't added by
>>>> 'len', was it?
>>>
>>> Actually, the correct thing may be like what did in the
>>> attached patch, as Maurizio discussed with me[1].
>>>
>>> Very interestingly, I have reproduced the problem one time
>>> with ext4/271 ext4/301 ext4/305, but won't with the attached
>>> patch after running it for 3 rounds.
>>>
>>> [tom@...alhost xfstests]$ sudo ./check ext4/271 ext4/301 ext4/305
>>> FSTYP         -- ext4
>>> PLATFORM      -- Linux/x86_64 localhost 3.15.0-rc7-next-20140527+
>>> MKFS_OPTIONS  -- /dev/vdc
>>> MOUNT_OPTIONS -- -o acl,user_xattr /dev/vdc /mnt/scratch
>>>
>>> ext4/271 1s ... 1s
>>> ext4/301 31s ... 32s
>>> ext4/305 181s ... 180s
>>> Ran: ext4/271 ext4/301 ext4/305
>>> Passed all 3 tests
>>>
>>> Jet, could you test the attached patch?
>>
>> sorry, could you specify which patch need me to test ?
>> actually I got confused. I only find
>
> Firstly, dongsu's patch is wrong, and it doesn't make sense to test
> that.
>
> Secondly, it is the patch attached in my last email, and the
> name is 'fix_compute_segments.patch'.
>
> Please let me know if you can find the patch, if you still can't, I
> may resend to you.
>

Just got your email which attached that patch, thanks. I guess there is some network problem on my side which leads to some latency.
Will test it out.

>
> Thanks,
>
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