From mboxrd@z Thu Jan  1 00:00:00 1970
From: Chris Wilson <chris@chris-wilson.co.uk>
Subject: Re: [PATCH 37/48] drm/i915: Defer request freeing
Date: Thu, 12 Dec 2013 11:08:47 +0000
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To: Ben Widawsky <benjamin.widawsky@intel.com>
Cc: Intel GFX <intel-gfx@lists.freedesktop.org>, Ben Widawsky <ben@bwidawsk.net>
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On Fri, Dec 06, 2013 at 02:11:22PM -0800, Ben Widawsky wrote:
> From: Ben Widawsky <ben@bwidawsk.net>
> 
> With context destruction, we always want to be able to tear down the
> underlying address space. This is invoked on the last unreference to the
> context which could happen before we've moved all objects to the
> inactive list. To enable a clean tear down the address space, make sure
> to process the request free lastly.
> 
> Without this change, we cannot guarantee to we don't still have active
> objects in the VM.
> 
> As an example of a failing case:
> CTX-A is created, count=1
> CTX-A is used during execbuf
> 	does a context switch count = 2
> 	and add_request count = 3
> CTX B runs, switches, CTX-A count = 2
> CTX-A is destroyed, count = 1
> retire requests is called
> 	free_request from CTX-A, count = 0 <--- free context with active object
> 
> As mentioned above, by doing the free request after processing the
> active list, we can avoid this case.

So just process the active_list first, the requests and objects
associated with the ring should be fairly independent.
-Chris

-- 
Chris Wilson, Intel Open Source Technology Centre