Re: [PATCH] drm/i915: Mark up i915_vma_unbind() as a potential sleeper

[Joonas Lahtinen <joonas.lahtinen@linux.intel.com>]

On Thu, 2017-11-09 at 10:59 +0000, Chris Wilson wrote:
> Whenever we want to unbind a vma, we must wait on all GPU activity to
> complete first. (This is what gives us the ability to do fine grained
> eviction and purging by only having to wait on the VMA that we need to
> unbind to proceed; though if pushed we can make it a rule that we are
> only allowed to unbind already idle VMA and move the burden of the work
> and organising the sleep onto the caller.) Currently, we might only
> sleep if the vma is still active on the GPU, but in principle
> i915_vma_unbind() always implies a sleep, so mark it up with a
> might_sleep().
> 
> Suggested-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
> Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
> Cc: Matthew Auld <matthew.william.auld@gmail.com>
> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>

<SNIP>

> +++ b/drivers/gpu/drm/i915/i915_vma.c
> @@ -743,6 +743,7 @@ int i915_vma_unbind(struct i915_vma *vma)
>  	/* First wait upon any activity as retiring the request may
>  	 * have side-effects such as unpinning or even unbinding this vma.
>  	 */
> +	might_sleep();

Please lift this up, even before lockdep_assert_held, for more clarity.

might_sleep();
lockdep_assert_held(...);

Reviewed-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>

Regards, Joonas
-- 
Joonas Lahtinen
Open Source Technology Center
Intel Corporation
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