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