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);
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));
--
2.41.0
