linux-kernel - Re: Re: [PATCH 5/7] media: cedrus: h265: Add a couple of error checks

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Date:   Tue, 12 Jul 2022 23:25:00 +0200
From:   Jernej Škrabec <jernej.skrabec@...il.com>
To:     Ezequiel Garcia <ezequiel@...guardiasur.com.ar>
Cc:     mripard@...nel.org, paul.kocialkowski@...tlin.com, wens@...e.org,
        samuel@...lland.org, mchehab@...nel.org,
        gregkh@...uxfoundation.org, hverkuil-cisco@...all.nl,
        linux-media@...r.kernel.org, linux-staging@...ts.linux.dev,
        linux-arm-kernel@...ts.infradead.org, linux-sunxi@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: Re: [PATCH 5/7] media: cedrus: h265: Add a couple of error checks

Hi Ezequiel.

Dne ponedeljek, 11. julij 2022 ob 23:31:11 CEST je Ezequiel Garcia napisal(a):
> On Mon, Jun 20, 2022 at 07:55:15PM +0200, Jernej Skrabec wrote:
> > Now that we have infrastructure for reporting errors, let's add two
> > checks, which will make sure slice can be actually decoded.
> > 
> > Signed-off-by: Jernej Skrabec <jernej.skrabec@...il.com>
> > ---
> > 
> >  drivers/staging/media/sunxi/cedrus/cedrus_h265.c | 8 ++++++++
> >  1 file changed, 8 insertions(+)
> > 
> > diff --git a/drivers/staging/media/sunxi/cedrus/cedrus_h265.c
> > b/drivers/staging/media/sunxi/cedrus/cedrus_h265.c index
> > cfde4ccf6011..99020b9f9ff8 100644
> > --- a/drivers/staging/media/sunxi/cedrus/cedrus_h265.c
> > +++ b/drivers/staging/media/sunxi/cedrus/cedrus_h265.c
> 
> Now that you've allowed setup to fail, I would suggest
> to have some documentation/comments on struct cedrus_dec_ops,
> to set the expectation/rules for each ops, including the
> call paths for each operation, which of them are allowed to sleep,
> etc.

Documentation can be always added, but it should be separate patch.

> 
> > @@ -435,9 +435,17 @@ static int cedrus_h265_setup(struct cedrus_ctx *ctx,
> > struct cedrus_run *run)> 
> >  	 * instead of start of slice data. Padding is 8 bits at most (one 
bit
> >  	 set to 1 and * at most seven bits set to 0), so we have to 
inspect
> >  	 only one byte before slice data. */
> > 
> > +
> > +	if (slice_params->data_byte_offset == 0)
> > +		return -EOPNOTSUPP;
> > +
> 
> AFAICS, cedrus_h265_setup is called from .device_run.
> We've been discussing control validation before, and I think the
> ideal place to do that is v4l2_ctrl_ops.s_ctrl, if that's
> at all possible.

Yeah, this particular check can be moved to s_ctrl handler.

> 
> Driver's mem2mem device_run are executed in the context
> of a work_struct and the failure won't really get reported
> up the stack.

Well, at least there will be a notice in dmesg. Not ideal, I know.

> 
> >  	padding = (u8 *)vb2_plane_vaddr(&run->src->vb2_buf, 0) +
> >  	
> >  		slice_params->data_byte_offset - 1;
> > 
> > +	/* at least one bit must be set in that byte */
> > +	if (*padding == 0)
> > +		return -EINVAL;
> > +
> 
> Maybe this is something to check at cedrus_buf_prepare(),
> when the buffer is queued?

I don't think so. This check is HEVC specific, but cedrus_buf_prepare() is not 
and we need to have slice control ready, which I'm not sure is the case for 
cedrus_buf_prepare().

Best regards,
Jernej

> 
> Thanks,
> Ezequiel
> 
> >  	for (count = 0; count < 8; count++)
> >  	
> >  		if (*padding & (1 << count))
> >  		
> >  			break;
> > 
> > --
> > 2.36.1