[PATCH 2/3] drm/vkms: stop generating CRCs on buffer overflow

[Rodrigo Siqueira]

Hi Oleg,

First of all, thank you for your patchset.

On 06/13, Daniel Vetter wrote:
> On Thu, Jun 13, 2019 at 03:18:01PM +0300, Oleg Vasilev wrote:
> > Because interrupts are generated artifitially, kernel bug may lead to
> > infinte attempts to submit CRC.
> > 
> > Signed-off-by: Oleg Vasilev <oleg.vasilev at intel.com>
> > ---
> >  drivers/gpu/drm/vkms/vkms_crc.c | 10 +++++++++-
> >  1 file changed, 9 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/vkms/vkms_crc.c b/drivers/gpu/drm/vkms/vkms_crc.c
> > index d7b409a3c0f8..bc717a8888b5 100644
> > --- a/drivers/gpu/drm/vkms/vkms_crc.c
> > +++ b/drivers/gpu/drm/vkms/vkms_crc.c
> > @@ -167,6 +167,7 @@ void vkms_crc_work_handle(struct work_struct *work)
> >  	u32 crc32 = 0;
> >  	u64 frame_start, frame_end;
> >  	unsigned long flags;
> > +	int ret;
> >  
> >  	spin_lock_irqsave(&out->state_lock, flags);
> >  	frame_start = crtc_state->frame_start;
> > @@ -202,7 +203,14 @@ void vkms_crc_work_handle(struct work_struct *work)
> >  	 * missing frames
> >  	 */
> >  	while (frame_start <= frame_end)
> > -		drm_crtc_add_crc_entry(crtc, true, frame_start++, &crc32);
> > +	{
> 
> Bikeshed: Kernel codingstyle puts this on the same line as the closing )
> of the while/if/for.

I recommend you to create a post-commit script in your git repo.
Something like this:

touch .git/hooks/post-commit

In the post-commit, add:

exec git show --format=email HEAD | ./scripts/checkpatch.pl --strict --codespell
 
> Aside from that not sure that's useful here, we've fixed the bug by now
> ...

IMHO, this patch is useful because it handles the return value from
drm_crtc_add_crc_entry() which make the code a little bit more reliable.
Additionally, it avoids polluting the dmesg output in case of a
problem.

> -Daniel
> 
> > +		ret = drm_crtc_add_crc_entry(crtc, true, frame_start++, &crc32);
> > +		if (ret) {
> > +			DRM_WARN("VKMS stop generating CRCs\n");
> > +			out->crc_enabled = false;
> > +			break;
> > +		}
> > +	}
> >  
> >  out:
> >  	/* to avoid using the same value for frame number again */
> > -- 
> > 2.21.0
> > 
> 
> -- 
> Daniel Vetter
> Software Engineer, Intel Corporation
> http://blog.ffwll.ch

-- 
Rodrigo Siqueira
https://siqueira.tech