Re: [PATCH 02/10] drm/i915/userptr: Make gup errors stickier

Mika Kuoppala
2016-08-15T15:08:53Z

Chris Wilson <chris@chris-wilson.co.uk> writes:

> Keep any error reported by the gup_worker until we are notified that the
> arena has changed (via the mmu-notifier). This has the importance of
> making two consecutive calls to i915_gem_object_get_pages() reporting
> the same error, and curtailing an loop of detecting a fault and requeueing
> a gup_worker.
>
> Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> ---
> drivers/gpu/drm/i915/i915_gem_userptr.c | 17 +++++++----------
> 1 file changed, 7 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
> index 57218cca7e05..be54825ef3e8 100644
> --- a/drivers/gpu/drm/i915/i915_gem_userptr.c
> +++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
> @@ -542,8 +542,6 @@ __i915_gem_userptr_get_pages_worker(struct work_struct *_work)
> }
> }
> obj->userptr.work = ERR_PTR(ret);
> - if (ret)
> - __i915_gem_userptr_set_active(obj, false);
> }
>
> obj->userptr.workers--;
> @@ -628,15 +626,14 @@ i915_gem_userptr_get_pages(struct drm_i915_gem_object *obj)
> * to the vma (discard or cloning) which should prevent the more
> * egregious cases from causing harm.
> */
> - if (IS_ERR(obj->userptr.work)) {
> - /* active flag will have been dropped already by the worker */
> - ret = PTR_ERR(obj->userptr.work);
> - obj->userptr.work = NULL;
> - return ret;
> - }
> - if (obj->userptr.work)
> +
> + if (obj->userptr.work) {
> /* active flag should still be held for the pending work */
> - return -EAGAIN;
> + if (IS_ERR(obj->userptr.work))
> + return PTR_ERR(obj->userptr.work);

Previously you did set the work to null before returning error,
now you dont.

Is it the responsibility of cancel_userptr now, through mm notifier,
that clears the pointer?

-Mika

> + else
> + return -EAGAIN;
> + }
>
> /* Let the mmu-notifier know that we have begun and need cancellation */
> ret = __i915_gem_userptr_set_active(obj, true);
> --
> 2.8.1
>
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