From: Daniel Vetter <daniel@ffwll.ch>
To: Chris Wilson <chris@chris-wilson.co.uk>,
Daniel Vetter <daniel@ffwll.ch>,
dri-devel@lists.freedesktop.org, intel-gfx@lists.freedesktop.org
Subject: Re: [PATCH v3 3/3] drm/vgem: Keep a reference to the dmabuf when mmaped
Date: Wed, 5 Oct 2016 15:42:13 +0200 [thread overview]
Message-ID: <20161005134213.GG20761@phenom.ffwll.local> (raw)
In-Reply-To: <20161005134009.GC22676@nuc-i3427.alporthouse.com>
On Wed, Oct 05, 2016 at 02:40:09PM +0100, Chris Wilson wrote:
> On Wed, Oct 05, 2016 at 03:11:00PM +0200, Daniel Vetter wrote:
> > On Fri, Sep 30, 2016 at 02:59:59PM +0100, Chris Wilson wrote:
> > > In order to keep the dmabuf alive whilst the mmap is, we need to hold a
> > > reference to the dmabuf and not the backing object. This is important as
> > > the dmabuf not only keeps the object alive, but also the device so that
> > >
> > > dmabuf = vgem_create_dmabuf();
> > > ptr = mmap(... dmabuf ...);
> > > close(dmabuf);
> > >
> > > persists across module-unload as well as device closure.
> >
> > I don't see where we grab the ref to the dma-buf here instead of the
> > backing storage. And doesn't the exact same issue happen when you use dumb
> > mmap? Or maybe I'm just a bit confused about what's going on here ...
>
> The reference to the dmabuf is in vma->vm_file, which was used to keep
> the module alive. So this might be overzealous, in that there shouldn't
> be a way to get back from the shmemfs object to the module. However,
> that does make me aware of a failure path we have in patches that do add
> callbacks from shmemfs to the driver...
>
> At least using the ptr after closing the module is ok. So this patch is
> not required.
I think if we entirely redirect the mmap to shmem, and not forget to also
update vm_file, the driver could get unloaded without ill effects. I'll
leave this one out for now, picked up 1&2 from v4 to -misc meanwhile.
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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next prev parent reply other threads:[~2016-10-05 13:42 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-09-30 13:59 [PATCH v3 1/3] drm/prime: Pass the right module owner through to dma_buf_export() Chris Wilson
2016-09-30 13:59 ` [PATCH v3 2/3] drm/prime: Take a ref on the drm_dev when exporting a dma_buf Chris Wilson
2016-09-30 13:59 ` [PATCH v3 3/3] drm/vgem: Keep a reference to the dmabuf when mmaped Chris Wilson
2016-10-05 13:11 ` Daniel Vetter
2016-10-05 13:40 ` Chris Wilson
2016-10-05 13:42 ` Daniel Vetter [this message]
2016-09-30 14:22 ` [PATCH v3 1/3] drm/prime: Pass the right module owner through to dma_buf_export() Christian König
2016-09-30 14:49 ` ✗ Fi.CI.BAT: warning for series starting with [v3,1/3] " Patchwork
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