Quoting Tvrtko Ursulin (2019-01-15 10:19:11)
>
> On 14/01/2019 21:17, Chris Wilson wrote:
> > @@ -620,40 +682,24 @@ static int i915_gem_userptr_get_pages(struct drm_i915_gem_object *obj)
> > return -EAGAIN;
> > }
> >
> > - pvec = NULL;
> > - pinned = 0;
> > + if (mm == current->mm && try_fast_gup(obj) == 0)
> > + return 0;
>
> Is try_fast_gup guaranteed to fail on ranges probe_range would have
> rejected?
If a page isn't present, it will fail. For our purposes that means
fast_gup fails for GGTT mmaps, as well as other ranges.
> > - if (mm == current->mm) {
> > - pvec = kvmalloc_array(num_pages, sizeof(struct page *),
> > - GFP_KERNEL |
> > - __GFP_NORETRY |
> > - __GFP_NOWARN);
> > - if (pvec) /* defer to worker if malloc fails */
> > - pinned = __get_user_pages_fast(obj->userptr.ptr,
> > - num_pages,
> > - !i915_gem_object_is_readonly(obj),
> > - pvec);
> > - }
> > + /* lockdep doesn't yet automatically allow nesting of readers */
> > + down_read_nested(&mm->mmap_sem, SINGLE_DEPTH_NESTING);
>
> Why is nesting needed - comment needs to explain.
We get called with mm->mmap_sem held for reading on a fault path, and
without mm->mmap_sem held otherwise. lockdep doesn't allow nesting of
readers, hence the comment.
-Chris
_______________________________________________
Intel-gfx mailing list
Intel-gfx@xxxxxxxxxxxxxxxxxxxxx
https://lists.freedesktop.org/mailman/listinfo/intel-gfx
