On 15/01/2019 10:30, Chris Wilson wrote:
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.
What if it has been pre-faulted?
- 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.
Something like that in the comment yes please. :)
Regards,
Tvrtko
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