[Intel-gfx] [PATCH] drm/i915: Clean up associated VMAs on context destruction

[Chris Wilson]

On Fri, Sep 11, 2015 at 03:31:33PM +0100, Tvrtko Ursulin wrote:
> From: Tvrtko Ursulin <tvrtko.ursulin at intel.com>
> 
> Prevent leaking VMAs and PPGTT VMs when objects are imported
> via flink.
> 
> Scenario is that any VMAs created by the importer will be left
> dangling after the importer exits, or destroys the PPGTT context
> with which they are associated.
> 
> This is caused by object destruction not running when the
> importer closes the buffer object handle due the reference held
> by the exporter. This also leaks the VM since the VMA has a
> reference on it.
> 
> In practice these leaks can be observed by stopping and starting
> the X server on a kernel with fbcon compiled in. Every time
> X server exits another VMA will be leaked against the fbcon's
> frame buffer object.
> 
> Also on systems where flink buffer sharing is used extensively,
> like Android, this leak has even more serious consequences.
> 
> This version is takes a general approach from the  earlier work
> by Rafael Barabalho (drm/i915: Clean-up PPGTT on context
> destruction) and tries to incorporate the subsequent discussion
> between Chris Wilson and Daniel Vetter.
> 
> On context destruction a VM is marked as closed and a worker
> thread scheduled to unbind all inactive VMAs for this VM. At
> the same time, active VMAs retired on this closed VM are
> unbound immediately.

You don't need a worker, since you just can just drop the vma from the
retirement.
http://cgit.freedesktop.org/~ickle/linux-2.6/commit/?h=nightly&id=9d4020dce054cca23bd1fea72092d036f0a3ea13

That patch is as old as the test case, just waiting for some review on
earlier code.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre