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

[Daniel Vetter]

On Mon, Jun 17, 2019 at 10:53:46PM -0300, Rodrigo Siqueira wrote:
> 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.

If it's the return value that annoys you, there's an easy fix: Let's
remove it! None of the other drivers look at it either.

Imo that's clearer than trying to do something reasonable when facing
driver bugs (which this is here).
-Daniel

> 
> > -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

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch