Re: [Linaro-mm-sig] [PATCH 04/18] dma-fence: prime lockdep annotations

Daniel Vetter
2020-06-18T14:42:49Z

On Wed, Jun 17, 2020 at 12:29:40PM -0300, Jason Gunthorpe wrote:
> On Wed, Jun 17, 2020 at 09:57:54AM +0200, Daniel Vetter wrote:
>
> > > At the very least I think there should be some big warning that
> > > dma_fence in notifiers should be avoided.
> >
> > Yeah I'm working on documentation, and also the notifiers here
> > hopefully make it clear it's massive pain. I think we could even make
> > a hard rule that dma_fence in mmu notifier outside of drivers/gpu is a
> > bug/misfeature.
>
> Yep!
>
> > Might be a good idea to add a MAINTAINERS entry with a K: regex
> > pattern, so that you can catch such modifiers. We do already have such
> > a pattern for dma-fence, to catch abuse. So if you want I could type
> > up a documentation patch for this, get your and others acks and the
> > dri-devel folks would enforce that the dma_fence_wait madness doesn't
> > leak beyond drivers/gpu
>
> It seems like the best thing

Just thought about where to best put this, and I think including it as
another paragraph in the next round of this series makes the most sense.
You'll get cc'ed for acking when that happens - might take a while since
there's a lot of details here all over to sort out.
-Daniel

>
> > Oded has agreed to remove the dma-fence usage, since they really don't
> > need it (and all the baggage that comes with it), plain old completion
> > is enough for their use. This use is also why I added the regex to
> > MAINTAINERS, so that in the future we can catch people who try to use
> > dma_fence because it looks cute and useful, and are completely
> > oblivious to all the pain and headaches involved.
>
> This is good!
>
> Thanks,
> Jason

--
Daniel Vetter
Software Engineer, Intel Corporation