[Intel-gfx] [PATCH 5/8] drm/i915: vma NULL pointer check

Tomas Elf tomas.elf at intel.com
Fri Oct 9 04:30:29 PDT 2015

On 09/10/2015 08:48, Chris Wilson wrote:
> On Thu, Oct 08, 2015 at 07:31:37PM +0100, Tomas Elf wrote:
>> Sometimes the iterated vma objects are NULL apparently. Be aware of this while
>> iterating and do early exit instead of causing a NULL pointer exception.
> Wrong.
> -Chris

So the NULL pointer exception that I ran into multiple times during 
several different test runs on the line that says "vma->pin_count" was 
not because the vma pointer was NULL. Would you mind sharing your 
explanation to how this might have happened? Is it because we're not 
synchronizing and there's no protection against the driver deallocating 
vmas while we're trying to capture them? If this all ties into the 
aforementioned RCU-based solution then maybe we should go with that then.


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