Re: Gem GTT mmaps..

[Thomas Hellström]

Jesse Barnes wrote:
> On Friday, February 6, 2009 1:35 pm Thomas Hellström wrote:
>   
> > Jesse Barnes wrote:
> >     
> > > On Thursday, February 5, 2009 10:37 am Jesse Barnes wrote:
> > >       
> > > > So if we leave the lookup reference around from the GTT mapping ioctl,
> > > > that would take care of new mappings.  And if we added/removed
> > > > references at VM open/close time, we should be covered for fork.  But is
> > > > it ok to add a new unref in the finish ioctl for GTT mapped objects?  I
> > > > don't think so, because we don't know for sure if the caller was the one
> > > > that created the new fake offset (which would be one way of detecting
> > > > whether it was GTT mapped). Seems like we need a new unmap ioctl?  Or we
> > > > could put the mapping ref/unref in libdrm, where it would be tracked on
> > > > a per-process basis...
> > > >         
> > > Ah but maybe we should just tear down the fake offset at unmap time; then
> > > we'd be able to use it as an existence test for the mapping and get the
> > > refcounting right.  The last thing I thought of was whether we'd be ok in
> > > a map_gtt -> crash case.  I *think* the vm_close code will deal with
> > > that, if we do a deref there?
> > >       
> > Yes, an mmap() is always paired with a vm_close(), and the vm_close()
> > also happens in a crash situation.
> >     
>
> This one should cover the cases you found.
>   - ref at map time will keep the object around so fault shouldn't fail
>   - additional threads will take their refs in vm_open/close
>   - unmap will unref and remove mmap_offset allowing object to be freed
>
>   
Jesse,

Yes, it looks OK to me.
A short question, though, when is i915_gem_sw_finish_ioctl called? Is it 
possible that the client may still think its mmap offset is valid?

Thomas




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