Re: [PATCH for v4.5] vb2: fix nasty vb2_thread regression

[Hans Verkuil <hverkuil@xs4all.nl>]

On 01/27/2016 09:57 PM, Matthias Schwarzott wrote:
> Am 27.01.2016 um 13:08 schrieb Hans Verkuil:
>> The vb2_thread implementation was made generic and was moved from
>> videobuf2-v4l2.c to videobuf2-core.c in commit af3bac1a. Unfortunately
>> that clearly was never tested since it broke read() causing NULL address
>> references.
>>
>> The root cause was confused handling of vb2_buffer vs v4l2_buffer (the pb
>> pointer in various core functions).
>>
>> The v4l2_buffer no longer exists after moving the code into the core and
>> it is no longer needed. However, the vb2_thread code passed a pointer to
>> a vb2_buffer to the core functions were a v4l2_buffer pointer was expected
>> and vb2_thread expected that the vb2_buffer fields would be filled in
>> correctly.
>>
>> This is obviously wrong since v4l2_buffer != vb2_buffer. Note that the
>> pb pointer is a void pointer, so no type-checking took place.
>>
>> This patch fixes this problem:
>>
>> 1) allow pb to be NULL for vb2_core_(d)qbuf. The vb2_thread code will use
>>    a NULL pointer here since they don't care about v4l2_buffer anyway.
>> 2) let vb2_core_dqbuf pass back the index of the received buffer. This is
>>    all vb2_thread needs: this index is the index into the q->bufs array
>>    and vb2_thread just gets the vb2_buffer from there.
>> 3) the fileio->b pointer (that originally contained a v4l2_buffer) is
>>    removed altogether since it is no longer needed.
>>
>> Tested with vivid and the cobalt driver.
>>
>> Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
>> Tested-by: Hans Verkuil <hans.verkuil@cisco.com>
>> Reported-by: Matthias Schwarzott <zzam@gentoo.org>
> 
> Hi Hans!
> 
> Thank you for this patch.
> I gave this patch a try on the latest sources from
> git://linuxtv.org/media_tree.git
> 
> Compiled for kernel 4.2.8 with media_build.
> 
> Now it no longer oopses.

Good.

> It tunes fine (according to femon), but I still do not get a
> picture/dvbtraffic reports nothing.

I will try to do a DVB test tomorrow. I can't spend too much time on it so
if I can't reproduce it I'll probably ask Mauro to take a look. After tomorrow
it will take at least a week before I have another chance of testing this due
to traveling.

Regards,

	Hans

> 
> Regards
> Matthias
> 
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