drm/shmem-helpers: Don't call get/put_pages on imported dma-buf in vmap

There's no direct harm, because for the shmem helpers these are noops
on imported buffers. The trouble is in the locks these take - I want
to change dma_buf_vmap locking, and so need to make sure that we only
ever take certain locks on one side of the dma-buf interface: Either
for exporters, or for importers.

v2: Change the control flow less compared to what's there (Thomas)

Tested-by: Boris Brezillon <boris.brezillon@collabora.com>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Rob Herring <robh@kernel.org>
Cc: Noralf Trønnes <noralf@tronnes.org>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200514202256.490926-1-daniel.vetter@ffwll.ch

diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c
index 3885854..0aac83e 100644 (file)
--- a/drivers/gpu/drm/drm_gem_shmem_helper.c
+++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
@@ -252,15 +252,15 @@ static void *drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem)
        if (shmem->vmap_use_count++ > 0)
                return shmem->vaddr;
 
-       ret = drm_gem_shmem_get_pages(shmem);
-       if (ret)
-               goto err_zero_use;
-
        if (obj->import_attach) {
                shmem->vaddr = dma_buf_vmap(obj->import_attach->dmabuf);
        } else {
                pgprot_t prot = PAGE_KERNEL;
 
+               ret = drm_gem_shmem_get_pages(shmem);
+               if (ret)
+                       goto err_zero_use;
+
                if (!shmem->map_cached)
                        prot = pgprot_writecombine(prot);
                shmem->vaddr = vmap(shmem->pages, obj->size >> PAGE_SHIFT,
@@ -276,7 +276,8 @@ static void *drm_gem_shmem_vmap_locked(struct drm_gem_shmem_object *shmem)
        return shmem->vaddr;
 
 err_put_pages:
-       drm_gem_shmem_put_pages(shmem);
+       if (!obj->import_attach)
+               drm_gem_shmem_put_pages(shmem);
 err_zero_use:
        shmem->vmap_use_count = 0;