On 8/8/23 09:21, Boris Brezillon wrote:
On Thu, 3 Aug 2023 18:52:20 +0200 Danilo Krummrich <dakr@xxxxxxxxxx> wrote:When no custom lock is set to protect a GEMs GPUVA list, lockdep checks should fall back to the GEM objects dma-resv lock. With the current implementation we're setting the lock_dep_map of the GEM objects 'resv' pointer (in case no custom lock_dep_map is set yet) on drm_gem_private_object_init(). However, the GEM objects 'resv' pointer might still change after drm_gem_private_object_init() is called, e.g. through ttm_bo_init_reserved(). This can result in the wrong lock being tracked. To fix this, call dma_resv_held() directly from drm_gem_gpuva_assert_lock_held() and fall back to the GEMs lock_dep_map pointer only if an actual custom lock is set. Fixes: e6303f323b1a ("drm: manager to keep track of GPUs VA mappings") Signed-off-by: Danilo Krummrich <dakr@xxxxxxxxxx>Reviewed-by: Boris Brezillon <boris.brezillon@xxxxxxxxxxxxx> but I'm wondering if it wouldn't be a good thing to add a drm_gem_set_resv() helper, so the core can control drm_gem_object::resv re-assignments (block them if it's happening after the GEM has been exposed to the outside world or update auxiliary data if it's happening before that).
I agree, this might be a good idea. There are quite a few places where drm_gem_object::resv is set from external code.
--- include/drm/drm_gem.h | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-) diff --git a/include/drm/drm_gem.h b/include/drm/drm_gem.h index c0b13c43b459..bc9f6aa2f3fe 100644 --- a/include/drm/drm_gem.h +++ b/include/drm/drm_gem.h @@ -551,15 +551,17 @@ int drm_gem_evict(struct drm_gem_object *obj); * @lock: the lock used to protect the gpuva list. The locking primitive * must contain a dep_map field. * - * Call this if you're not proctecting access to the gpuva list - * with the dma-resv lock, otherwise, drm_gem_gpuva_init() takes care - * of initializing lock_dep_map for you. + * Call this if you're not proctecting access to the gpuva list with the + * dma-resv lock, but with a custom lock. */ #define drm_gem_gpuva_set_lock(obj, lock) \ - if (!(obj)->gpuva.lock_dep_map) \ + if (!WARN((obj)->gpuva.lock_dep_map, \ + "GEM GPUVA lock should be set only once.")) \ (obj)->gpuva.lock_dep_map = &(lock)->dep_map #define drm_gem_gpuva_assert_lock_held(obj) \ - lockdep_assert(lock_is_held((obj)->gpuva.lock_dep_map)) + lockdep_assert((obj)->gpuva.lock_dep_map ? \ + lock_is_held((obj)->gpuva.lock_dep_map) : \ + dma_resv_held((obj)->resv)) #else #define drm_gem_gpuva_set_lock(obj, lock) do {} while (0) #define drm_gem_gpuva_assert_lock_held(obj) do {} while (0) @@ -573,11 +575,12 @@ int drm_gem_evict(struct drm_gem_object *obj); * * Calling this function is only necessary for drivers intending to support the * &drm_driver_feature DRIVER_GEM_GPUVA. + * + * See also drm_gem_gpuva_set_lock(). */ static inline void drm_gem_gpuva_init(struct drm_gem_object *obj) { INIT_LIST_HEAD(&obj->gpuva.list); - drm_gem_gpuva_set_lock(obj, &obj->resv->lock.base); }/**
