drm/ttm: Clear the ghost cpu_writers flag on ttm_buffer_object_transfer.

commit 0fbecd400dd0a82d465b3086f209681e8c54cb0f upstream.

It makes sense for a BO to move after a process has requested
exclusive RW access on it (e.g. because the BO used to be located in
unmappable VRAM and we intercepted the CPU access from the fault
handler).

If we let the ghost object inherit cpu_writers from the original
object, ttm_bo_release_list() will raise a kernel BUG when the ghost
object is destroyed. This can be reproduced with the nouveau driver on
nv5x.

Reported-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Tested-by: Marcin Slusarz <marcin.slusarz@gmail.com>
Signed-off-by: Francisco Jerez <currojerez@riseup.net>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/drivers/gpu/drm/ttm/ttm_bo_util.c b/drivers/gpu/drm/ttm/ttm_bo_util.c
index d764e82e799b4a264618a723ad66d46aa3e9b217..fe04f8c5ee5d4503bc5c57d594677157697573df 100644 (file)
--- a/drivers/gpu/drm/ttm/ttm_bo_util.c
+++ b/drivers/gpu/drm/ttm/ttm_bo_util.c
@@ -327,6 +327,7 @@ static int ttm_buffer_object_transfer(struct ttm_buffer_object *bo,
        INIT_LIST_HEAD(&fbo->lru);
        INIT_LIST_HEAD(&fbo->swap);
        fbo->vm_node = NULL;
+       atomic_set(&fbo->cpu_writers, 0);
 
        fbo->sync_obj = driver->sync_obj_ref(bo->sync_obj);
        if (fbo->mem.mm_node)