drm/gem-shmem: Acquire reservation lock in GEM pin/unpin callbacks

Export drm_gem_shmem_pin_locked() and acquire the reservation lock
directly in GEM pin callback. Same for unpin. Prepares for further
changes.

Dma-buf locking semantics require callers to hold the buffer's
reservation lock when invoking the pin and unpin callbacks. Prepare
gem-shmem accordingly by pushing locking out of the implementation.
A follow-up patch will fix locking for all GEM code at once.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Dmitry Osipenko <dmitry.osipenko@collabora.com>
Tested-by: Dmitry Osipenko <dmitry.osipenko@collabora.com> # virtio-gpu
Acked-by: Christian König <christian.koenig@amd.com>
Acked-by: Zack Rusin <zack.rusin@broadcom.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240227113853.8464-2-tzimmermann@suse.de

drivers/gpu/drm/drm_gem_shmem_helper.c

@@ -228,7 +228,7 @@ void drm_gem_shmem_put_pages(struct drm_gem_shmem_object *shmem)
 }
 EXPORT_SYMBOL(drm_gem_shmem_put_pages);
 
-static int drm_gem_shmem_pin_locked(struct drm_gem_shmem_object *shmem)
+int drm_gem_shmem_pin_locked(struct drm_gem_shmem_object *shmem)
 {
 	int ret;
 
@@ -238,13 +238,15 @@ static int drm_gem_shmem_pin_locked(struct drm_gem_shmem_object *shmem)
 
 	return ret;
 }
+EXPORT_SYMBOL(drm_gem_shmem_pin_locked);
 
-static void drm_gem_shmem_unpin_locked(struct drm_gem_shmem_object *shmem)
+void drm_gem_shmem_unpin_locked(struct drm_gem_shmem_object *shmem)
 {
 	dma_resv_assert_held(shmem->base.resv);
 
 	drm_gem_shmem_put_pages(shmem);
 }
+EXPORT_SYMBOL(drm_gem_shmem_unpin_locked);
 
 /**
  * drm_gem_shmem_pin - Pin backing pages for a shmem GEM object

include/drm/drm_gem_shmem_helper.h

@@ -108,6 +108,9 @@ void drm_gem_shmem_vunmap(struct drm_gem_shmem_object *shmem,
 			  struct iosys_map *map);
 int drm_gem_shmem_mmap(struct drm_gem_shmem_object *shmem, struct vm_area_struct *vma);
 
+int drm_gem_shmem_pin_locked(struct drm_gem_shmem_object *shmem);
+void drm_gem_shmem_unpin_locked(struct drm_gem_shmem_object *shmem);
+
 int drm_gem_shmem_madvise(struct drm_gem_shmem_object *shmem, int madv);
 
 static inline bool drm_gem_shmem_is_purgeable(struct drm_gem_shmem_object *shmem)
@@ -172,8 +175,15 @@ static inline void drm_gem_shmem_object_print_info(struct drm_printer *p, unsign
 static inline int drm_gem_shmem_object_pin(struct drm_gem_object *obj)
 {
 	struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
+	int ret;
+
+	ret = dma_resv_lock_interruptible(shmem->base.resv, NULL);
+	if (ret)
+		return ret;
+	ret = drm_gem_shmem_pin_locked(shmem);
+	dma_resv_unlock(shmem->base.resv);
 
-	return drm_gem_shmem_pin(shmem);
+	return ret;
 }
 
 /**
@@ -187,7 +197,9 @@ static inline void drm_gem_shmem_object_unpin(struct drm_gem_object *obj)
 {
 	struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj);
 
-	drm_gem_shmem_unpin(shmem);
+	dma_resv_lock(shmem->base.resv, NULL);
+	drm_gem_shmem_unpin_locked(shmem);
+	dma_resv_unlock(shmem->base.resv);
 }
 
 /**