linux-kernel - Re: [PATCH] media: dvb_ringbuffer : Fix a bug in dvb

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Date:   Fri, 9 Sep 2022 16:46:13 +0200
From:   Hans Petter Selasky <hps@...asky.org>
To:     유용수 <yongsuyoo0215@...il.com>,
        Kieran Bingham <kieran.bingham@...asonboard.com>,
        linux-media@...r.kernel.org, linux-kernel@...r.kernel.org,
        mchehab@...nel.org
Cc:     0215yys@...mail.net
Subject: Re: [PATCH] media: dvb_ringbuffer : Fix a bug in dvb_ringbuffer.c

On 8/31/22 15:45, 유용수 wrote:
> Dear All,
> 
> Can you share how this patch is going ?
> 
> 2022년 8월 18일 (목) 오후 9:55, 유용수 <yongsuyoo0215@...il.com>님이 작성:
>>
>> Dear All,
>>
>> Can you pay your attention to this patch ?
>> This is a very simple modification.
>> But, too much time has already passed since I sent the first E-mail.
>>
>> 2022년 8월 3일 (수) 오후 9:04, 유용수 <yongsuyoo0215@...il.com>님이 작성:
>>>
>>> Dear All.
>>> Too much time has already passed since I first sent this Email.
>>> Can you share how this patch is going ?
>>>
>>> 2022년 6월 23일 (목) 오후 6:11, 유용수 <yongsuyoo0215@...il.com>님이 작성:
>>>>
>>>> Dear Kieran Bingham
>>>>
>>>> I sent E-mail again by Linux terminal by using the command " ... git
>>>> send-email .."
>>>> I believe that you will surely get the diff file.
>>>>
>>>> Thank you
>>>>
>>>> 2022년 6월 22일 (수) 오후 10:12, Hans Petter Selasky <hps@...asky.org>님이 작성:
>>>>>
>>>>> Hi Kieran,
>>>>>
>>>>> The consumed variable should not be negative. This bug has been there
>>>>> since the beginning of the GIT at Linux from what I can see.
>>>>>
>>>>> +1
>>>>>
>>>>> --HPS
>>>>>
>>>>>   From 108c6acb2cc4bc4314b96f6f254a04b2873a096c Mon Sep 17 00:00:00 2001
>>>>> From: YongSu Yoo <yongsuyoo0215@...il.com>
>>>>> Date: Sun, 22 May 2022 04:53:12 +0000
>>>>> Subject: [PATCH] media: dvb_ringbuffer : Fix a bug in dvb_ringbuffer.c
>>>>>
>>>>> Signed-off-by:Yongsu Yoo <yongsuyoo0215@...il.com>
>>>>>
>>>>> The function dvb_ringbuffer_pkt_next in
>>>>> /linux-next/drviers/media/dvb-core/dvb_ringbuffer.c,
>>>>> which searches the idx of the next valid packet in the ring
>>>>> buffer of the ca->slot_info[slot].rx_buffer at
>>>>> /linux-next/drivers/media/dvb-core/dvb_ca_en50221.c,
>>>>> has the following problem.
>>>>> In calculating the amounts of the consumed address of the ring
>>>>> buffer, if the read address(rbuf->pread) of the ring buffer is
>>>>> smaller than the idx, the amounts of the searched address
>>>>> should be (idx - rbuf->pread),
>>>>> whereas if the read address(rbuf->pread) of the ring buffer is
>>>>> larger than the idx, the amounts of the consumed address should
>>>>> be (idx - rbuf->pread + rbug->size). But there exists an
>>>>> incorrect logic that the rbug-size was not properly added on
>>>>> (idx - rbug->pread) in the later case. With this commit, we
>>>>> fixed this bug.
>>>>> ---
>>>>>    drivers/media/dvb-core/dvb_ringbuffer.c | 4 +++-
>>>>>    1 file changed, 3 insertions(+), 1 deletion(-)
>>>>>
>>>>> diff --git a/drivers/media/dvb-core/dvb_ringbuffer.c
>>>>> b/drivers/media/dvb-core/dvb_ringbuffer.c
>>>>> index d1d471af0636..7d4558de8e83 100644
>>>>> --- a/drivers/media/dvb-core/dvb_ringbuffer.c
>>>>> +++ b/drivers/media/dvb-core/dvb_ringbuffer.c
>>>>> @@ -335,7 +335,9 @@ ssize_t dvb_ringbuffer_pkt_next(struct
>>>>> dvb_ringbuffer *rbuf, size_t idx, size_t*
>>>>>                  idx = (idx + curpktlen + DVB_RINGBUFFER_PKTHDRSIZE) % rbuf->size;
>>>>>          }
>>>>>
>>>>> -       consumed = (idx - rbuf->pread) % rbuf->size;
>>>>> +       consumed = (idx - rbuf->pread);
>>>>> +       if (consumed < 0)
>>>>> +               consumed += rbuf->size;
>>>>>
>>>>>          while((dvb_ringbuffer_avail(rbuf) - consumed) >
>>>>> DVB_RINGBUFFER_PKTHDRSIZE) {
>>>>>
>>>>> --
>>>>> 2.17.1

Maybe it will help if you write a test C-program to show the bad numbers 
computed?

--HPS