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.
v2: Rebase and rename a variable to avoid 80cols
v3: Mention v2
Signed-off-by: Chris Wilson <chris@xxxxxxxxxxxxxxxxxx>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxx>
---
drivers/gpu/drm/i915/i915_gem_userptr.c | 32 ++++++++++++++++----------------
1 file changed, 16 insertions(+), 16 deletions(-)
diff --git a/drivers/gpu/drm/i915/i915_gem_userptr.c b/drivers/gpu/drm/i915/i915_gem_userptr.c
index d11901d590ac..800a5394aa1e 100644
--- a/drivers/gpu/drm/i915/i915_gem_userptr.c
+++ b/drivers/gpu/drm/i915/i915_gem_userptr.c
@@ -571,25 +571,25 @@ __i915_gem_userptr_get_pages_worker(struct work_struct *_work)
struct get_pages_work *work = container_of(_work, typeof(*work), work);
struct drm_i915_gem_object *obj = work->obj;
struct drm_device *dev = obj->base.dev;
- const int num_pages = obj->base.size >> PAGE_SHIFT;
+ const int npages = obj->base.size >> PAGE_SHIFT;
struct page **pvec;
int pinned, ret;
ret = -ENOMEM;
pinned = 0;
- pvec = kmalloc(num_pages*sizeof(struct page *),
+ pvec = kmalloc(npages*sizeof(struct page *),
GFP_TEMPORARY | __GFP_NOWARN | __GFP_NORETRY);
if (pvec == NULL)
- pvec = drm_malloc_ab(num_pages, sizeof(struct page *));
+ pvec = drm_malloc_ab(npages, sizeof(struct page *));
if (pvec != NULL) {
struct mm_struct *mm = obj->userptr.mm->mm;
down_read(&mm->mmap_sem);
- while (pinned < num_pages) {
+ while (pinned < npages) {
ret = get_user_pages(work->task, mm,
obj->userptr.ptr + pinned * PAGE_SIZE,
- num_pages - pinned,
+ npages - pinned,
!obj->userptr.read_only, 0,
pvec + pinned, NULL);
if (ret < 0)
@@ -601,20 +601,20 @@ __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 = __i915_gem_userptr_set_pages(obj, pvec, num_pages);
- if (ret == 0) {
- list_add_tail(&obj->global_list, &to_i915(dev)->mm.unbound_list);
- obj->get_page.sg = obj->pages->sgl;
- obj->get_page.last = 0;
-
- pinned = 0;
+ if (obj->userptr.work == &work->work) {
+ if (pinned == npages) {
+ ret = __i915_gem_userptr_set_pages(obj, pvec, npages);
+ if (ret == 0) {
+ list_add_tail(&obj->global_list,
+ &to_i915(dev)->mm.unbound_list);
+ obj->get_page.sg = obj->pages->sgl;
+ obj->get_page.last = 0;
+ 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);
--
2.5.1
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