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    SubjectRe: [Linaro-mm-sig] [PATCH 04/18] dma-fence: prime lockdep annotations
    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
    http://blog.ffwll.ch

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