On Tue, Jun 30, 2015 at 05:55:31PM +0100, Chris Wilson wrote:
> The userptr worker allows for a slight race condition where upon there
> may two or more threads calling get_user_pages for the same object. When
> we have the array of pages, then we serialise the update of the object.
> However, the worker should only overwrite the obj->userptr.work pointer
> if and only if it is the active one. Currently we clear it for a
> secondary worker with the effect that we may rarely force a second
> lookup.
>
> Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Whole series:
Tested-by: Michał Winiarski <michal.winiarski@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/i915_gem_userptr.c | 16 ++++++++--------
> 1 file changed, 8 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
> index 7a5242cd5ea5..cb367d9f7909 100644
> --- a/drivers/gpu/drm/i915/i915_gem_userptr.c
> +++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
> @@ -581,17 +581,17 @@ __i915_gem_userptr_get_pages_worker(struct work_struct *_work)
> }
>
> mutex_lock(&dev->struct_mutex);
> - if (obj->userptr.work != &work->work) {
> - ret = 0;
> - } else if (pinned == num_pages) {
> - ret = st_set_pages(&obj->pages, pvec, num_pages);
> - if (ret == 0) {
> - list_add_tail(&obj->global_list, &to_i915(dev)->mm.unbound_list);
> - pinned = 0;
> + if (obj->userptr.work == &work->work) {
> + if (pinned == num_pages) {
> + ret = st_set_pages(&obj->pages, pvec, num_pages);
> + if (ret == 0) {
> + list_add_tail(&obj->global_list, &to_i915(dev)->mm.unbound_list);
> + pinned = 0;
> + }
> }
> + obj->userptr.work = ERR_PTR(ret);
> }
>
> - obj->userptr.work = ERR_PTR(ret);
> obj->userptr.workers--;
> drm_gem_object_unreference(&obj->base);
> mutex_unlock(&dev->struct_mutex);
> --
> 2.1.4
>
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