On 06/10/15 10:34, Chris Wilson wrote:
On Tue, Oct 06, 2015 at 11:28:49AM +0200, Daniel Vetter wrote:
On Tue, Oct 06, 2015 at 10:04:31AM +0100, Chris Wilson wrote:
On Tue, Oct 06, 2015 at 10:58:01AM +0200, Daniel Vetter wrote:
On Mon, Oct 05, 2015 at 01:26:36PM +0100, Tvrtko Ursulin wrote:
From: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
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 Barbalho (drm/i915: Clean-up PPGTT on context
destruction) and tries to incorporate the subsequent discussion
between Chris Wilson and Daniel Vetter.
v2:
Removed immediate cleanup on object retire - it was causing a
recursive VMA unbind via i915_gem_object_wait_rendering. And
it is in fact not even needed since by definition context
cleanup worker runs only after the last context reference has
been dropped, hence all VMAs against the VM belonging to the
context are already on the inactive list.
v3:
Previous version could deadlock since VMA unbind waits on any
rendering on an object to complete. Objects can be busy in a
different VM which would mean that the cleanup loop would do
the wait with the struct mutex held.
This is an even simpler approach where we just unbind VMAs
without waiting since we know all VMAs belonging to this VM
are idle, and there is nothing in flight, at the point
context destructor runs.
v4:
Double underscore prefix for __915_vma_unbind_no_wait and a
commit message typo fix. (Michel Thierry)
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
Testcase: igt/gem_ppgtt.c/flink-and-exit-vma-leak
Reviewed-by: Michel Thierry <michel.thierry@xxxxxxxxx>
Cc: Daniel Vetter <daniel.vetter@xxxxxxxx>
Cc: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Cc: Rafael Barbalho <rafael.barbalho@xxxxxxxxx>
Cc: Michel Thierry <michel.thierry@xxxxxxxxx>
Queued for -next, thanks for the patch.
Please no, it's an awful patch and does not even fix the root cause of
the leak (that the vma are not closed when the handle is).
It's a lose-lose situation for me as maintainer (and this holds in general
really, not just for this patch):
- Either I wield my considerable maintainer powers and force proper
solution, which will piss of a lot of people.
- Or I just merge intermediate stuff and piss of another set of people
(including likely our all future selves because we're slowly digging a
tech debt grave).
What I can't do with maintainer fu is force collaboration, I can only try
to piss off everyone equally. And today the die rolled a "merge".
Pity it didn't roll "what's the impact and where is the bugzilla?" :)
There is this one:
https://bugs.freedesktop.org/show_bug.cgi?id=87729
And I could raise another one for leaking VMAs on X.org restart? :)
Tvrtko
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