linux-kernel - Re: [PATCH 1/1] videobuf: Initialize lists in videobuf

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Date:	Wed, 17 Nov 2010 08:52:53 +0100
From:	Hans Verkuil <hverkuil@...all.nl>
To:	"Figo.zhang" <zhangtianfei@...dcoretech.com>
Cc:	Andrew Chew <AChew@...dia.com>,
	"pawel@...iak.com" <pawel@...iak.com>,
	"linux-media@...r.kernel.org" <linux-media@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] videobuf: Initialize lists in videobuf_buffer.

On Wednesday, November 17, 2010 08:16:27 Figo.zhang wrote:
> On 11/17/2010 03:11 PM, Hans Verkuil wrote:
> > On Wednesday, November 17, 2010 02:38:09 Andrew Chew wrote:
> >>>> diff --git a/drivers/media/video/videobuf-dma-contig.c
> >>> b/drivers/media/video/videobuf-dma-contig.c
> >>>> index c969111..f7e0f86 100644
> >>>> --- a/drivers/media/video/videobuf-dma-contig.c
> >>>> +++ b/drivers/media/video/videobuf-dma-contig.c
> >>>> @@ -193,6 +193,8 @@ static struct videobuf_buffer
> >>> *__videobuf_alloc_vb(size_t size)
> >>>>    	if (vb) {
> >>>>    		mem = vb->priv = ((char *)vb) + size;
> >>>>    		mem->magic = MAGIC_DC_MEM;
> >>>> +		INIT_LIST_HEAD(&vb->stream);
> >>>> +		INIT_LIST_HEAD(&vb->queue);
> >>>
> >>> i think it no need to be init, it just a list-entry.
> >>
> >> Okay, if that's really the case, then sh_mobile_ceu_camera.c, pxa_camera.c, mx1_camera.c, mx2_camera.c, and omap1_camera.c needs to be fixed to remove that WARN_ON(!list_empty(&vb->queue)); in their videobuf_prepare() methods, because those WARN_ON's are assuming that vb->queue is properly initialized as a list head.
> >>
> >> Which will it be?
> >>
> >
> > These list entries need to be inited. It is bad form to have uninitialized
> > list entries. It is not as if this is a big deal to initialize them properly.
> 
> in kernel source code, list entry are not often to be inited.
> 
> for example, see mm/vmscan.c register_shrinker(), no one init the 
> shrinker->list.
> 
> another example: see mm/swapfile.c  add_swap_extent(), no one init the
> new_se->list.

I have to think some more about this. I'll get back to this today. BTW, I do
agree that the WARN_ON's are bogus and should be removed.

And BTW, this isn't going to work either (mx1_camera.c):

static int mx1_camera_setup_dma(struct mx1_camera_dev *pcdev)
{
        struct videobuf_buffer *vbuf = &pcdev->active->vb;
        struct device *dev = pcdev->icd->dev.parent;
        int ret;

        if (unlikely(!pcdev->active)) {
                dev_err(dev, "DMA End IRQ with no active buffer\n");
                return -EFAULT;
        }

The vbuf assignment should be moved after the 'if'.

Regards,

	Hans

-- 
Hans Verkuil - video4linux developer - sponsored by Cisco
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