Re: [PATCH v6 6/6] drm/i915/gvt: Adding interface so user space can get the dma-buf

From	Gerd Hoffmann <kraxel@redhat.com>
Newsgroups	linux.kernel
Subject	Re: [PATCH v6 6/6] drm/i915/gvt: Adding interface so user space can get the dma-buf
Date	2017-06-02 17:30 +0200
Message-ID	<tNWGu-2XT-13@gated-at.bofh.it> (permalink)
References	(2 earlier) <tNCHM-61B-17@gated-at.bofh.it> <tNLrI-3yD-21@gated-at.bofh.it> <tNLBn-3BC-3@gated-at.bofh.it> <tNRdM-7Cl-19@gated-at.bofh.it> <tNWds-2wl-15@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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  Hi,

> > When i915's dma-buf's release() callback is called it will try to
> > free the gem object associated with the dma-buf if its ref count is
> > 0. But in our case the ref count is 1 so no free callback is called
> > so we can not release allocations there.

Why the ref count is one?  Who holds a reference and why?
Maybe it should be the other way around, i.e. the dmabuf holds a
reference on the vgpu instance backing it, i.e. you can't delete the
vgpu while dma-bufs exist?

> We cannot simply say that the user isn't allowed to release them in
> that order.

Yep, not going to fly.  Can happen even unintentionally because we can
pass around dmabufs to other processes.  Example: qemu passes dmabuf to
spice-client, then qemu crashes.  mgmt fd is closed before dmabuf fd
then.  The kernel must be able to handle that.

cheers,
  Gerd

Thread

[PATCH v6 6/6] drm/i915/gvt: Adding interface so user space can get the dma-buf Xiaoguang Chen <xiaoguang.chen@intel.com> - 2017-05-27 10:50 +0200
  Re: [PATCH v6 6/6] drm/i915/gvt: Adding interface so user space can  get the dma-buf Alex Williamson <alex.williamson@redhat.com> - 2017-06-01 20:10 +0200
    RE: [PATCH v6 6/6] drm/i915/gvt: Adding interface so user space can  get the dma-buf "Chen, Xiaoguang" <xiaoguang.chen@intel.com> - 2017-06-02 05:30 +0200
      Re: [PATCH v6 6/6] drm/i915/gvt: Adding interface so user space can  get the dma-buf Alex Williamson <alex.williamson@redhat.com> - 2017-06-02 05:40 +0200
        RE: [PATCH v6 6/6] drm/i915/gvt: Adding interface so user space can  get the dma-buf "Chen, Xiaoguang" <xiaoguang.chen@intel.com> - 2017-06-02 11:40 +0200
          Re: [PATCH v6 6/6] drm/i915/gvt: Adding interface so user space can  get the dma-buf Alex Williamson <alex.williamson@redhat.com> - 2017-06-02 17:00 +0200
            Re: [PATCH v6 6/6] drm/i915/gvt: Adding interface so user space can  get the dma-buf Gerd Hoffmann <kraxel@redhat.com> - 2017-06-02 17:30 +0200
              RE: [PATCH v6 6/6] drm/i915/gvt: Adding interface so user space can  get the dma-buf "Chen, Xiaoguang" <xiaoguang.chen@intel.com> - 2017-06-05 04:40 +0200
                Re: [PATCH v6 6/6] drm/i915/gvt: Adding interface so user space can  get the dma-buf Gerd Hoffmann <kraxel@redhat.com> - 2017-06-06 09:40 +0200

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