On Sun, 27 Aug 2023 20:54:43 +0300 Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx> wrote: > In a preparation of adding drm-shmem memory shrinker, move all reservation > locking lockdep checks to use new drm_gem_shmem_resv_assert_held() that > will resolve spurious lockdep warning about wrong locking order vs > fs_reclam code paths during freeing of shmem GEM, where lockdep isn't > aware that it's impossible to have locking contention with the fs_reclam > at this special time. > > Signed-off-by: Dmitry Osipenko <dmitry.osipenko@xxxxxxxxxxxxx> > --- > drivers/gpu/drm/drm_gem_shmem_helper.c | 37 +++++++++++++++++--------- > 1 file changed, 25 insertions(+), 12 deletions(-) > > diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c > index d96fee3d6166..ca5da976aafa 100644 > --- a/drivers/gpu/drm/drm_gem_shmem_helper.c > +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c > @@ -128,6 +128,23 @@ struct drm_gem_shmem_object *drm_gem_shmem_create(struct drm_device *dev, size_t > } > EXPORT_SYMBOL_GPL(drm_gem_shmem_create); > > +static void drm_gem_shmem_resv_assert_held(struct drm_gem_shmem_object *shmem) > +{ > + /* > + * Destroying the object is a special case.. drm_gem_shmem_free() > + * calls many things that WARN_ON if the obj lock is not held. But > + * acquiring the obj lock in drm_gem_shmem_free() can cause a locking > + * order inversion between reservation_ww_class_mutex and fs_reclaim. > + * > + * This deadlock is not actually possible, because no one should > + * be already holding the lock when drm_gem_shmem_free() is called. > + * Unfortunately lockdep is not aware of this detail. So when the > + * refcount drops to zero, we pretend it is already locked. > + */ > + if (kref_read(&shmem->base.refcount)) > + drm_gem_shmem_resv_assert_held(shmem); > +} > + > /** > * drm_gem_shmem_free - Free resources associated with a shmem GEM object > * @shmem: shmem GEM object to free > @@ -142,8 +159,6 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem) > if (obj->import_attach) { > drm_prime_gem_destroy(obj, shmem->sgt); > } else if (!shmem->imported_sgt) { > - dma_resv_lock(shmem->base.resv, NULL); > - > drm_WARN_ON(obj->dev, kref_read(&shmem->vmap_use_count)); > > if (shmem->sgt) { > @@ -156,8 +171,6 @@ void drm_gem_shmem_free(struct drm_gem_shmem_object *shmem) > drm_gem_shmem_put_pages_locked(shmem); AFAICT, drm_gem_shmem_put_pages_locked() is the only function that's called in the free path and would complain about resv-lock not being held. I think I'd feel more comfortable if we were adding a drm_gem_shmem_free_pages() function that did everything drm_gem_shmem_put_pages_locked() does except for the lock_held() check and the refcount dec, and have it called here (and in drm_gem_shmem_put_pages_locked()). This way we can keep using dma_resv_assert_held() instead of having our own variant. > > drm_WARN_ON(obj->dev, kref_read(&shmem->pages_use_count)); > - > - dma_resv_unlock(shmem->base.resv); > } > > drm_gem_object_release(obj); > @@ -170,7 +183,7 @@ static int drm_gem_shmem_get_pages_locked(struct drm_gem_shmem_object *shmem) > struct drm_gem_object *obj = &shmem->base; > struct page **pages; > > - dma_resv_assert_held(shmem->base.resv); > + drm_gem_shmem_resv_assert_held(shmem); > > if (kref_get_unless_zero(&shmem->pages_use_count)) > return 0; > @@ -228,7 +241,7 @@ static void drm_gem_shmem_kref_release_pages(struct kref *kref) > */ > void drm_gem_shmem_put_pages_locked(struct drm_gem_shmem_object *shmem) > { > - dma_resv_assert_held(shmem->base.resv); > + drm_gem_shmem_resv_assert_held(shmem); > > kref_put(&shmem->pages_use_count, drm_gem_shmem_kref_release_pages); > } > @@ -252,7 +265,7 @@ static int drm_gem_shmem_pin_locked(struct drm_gem_shmem_object *shmem) > { > int ret; > > - dma_resv_assert_held(shmem->base.resv); > + drm_gem_shmem_resv_assert_held(shmem); > > if (kref_get_unless_zero(&shmem->pages_pin_count)) > return 0; > @@ -276,7 +289,7 @@ static void drm_gem_shmem_kref_unpin_pages(struct kref *kref) > > static void drm_gem_shmem_unpin_locked(struct drm_gem_shmem_object *shmem) > { > - dma_resv_assert_held(shmem->base.resv); > + drm_gem_shmem_resv_assert_held(shmem); > > kref_put(&shmem->pages_pin_count, drm_gem_shmem_kref_unpin_pages); > } > @@ -357,7 +370,7 @@ int drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem, > } else { > pgprot_t prot = PAGE_KERNEL; > > - dma_resv_assert_held(shmem->base.resv); > + drm_gem_shmem_resv_assert_held(shmem); > > if (kref_get_unless_zero(&shmem->vmap_use_count)) { > iosys_map_set_vaddr(map, shmem->vaddr); > @@ -426,7 +439,7 @@ void drm_gem_shmem_vunmap_locked(struct drm_gem_shmem_object *shmem, > if (obj->import_attach) { > dma_buf_vunmap(obj->import_attach->dmabuf, map); > } else { > - dma_resv_assert_held(shmem->base.resv); > + drm_gem_shmem_resv_assert_held(shmem); > kref_put(&shmem->vmap_use_count, drm_gem_shmem_kref_vunmap); > } > > @@ -462,7 +475,7 @@ drm_gem_shmem_create_with_handle(struct drm_file *file_priv, > */ > int drm_gem_shmem_madvise_locked(struct drm_gem_shmem_object *shmem, int madv) > { > - dma_resv_assert_held(shmem->base.resv); > + drm_gem_shmem_resv_assert_held(shmem); > > if (shmem->madv >= 0) > shmem->madv = madv; > @@ -478,7 +491,7 @@ void drm_gem_shmem_purge_locked(struct drm_gem_shmem_object *shmem) > struct drm_gem_object *obj = &shmem->base; > struct drm_device *dev = obj->dev; > > - dma_resv_assert_held(shmem->base.resv); > + drm_gem_shmem_resv_assert_held(shmem); > > drm_WARN_ON(obj->dev, !drm_gem_shmem_is_purgeable(shmem)); >