mm: introduce vma_set_file function v5

Add the new vma_set_file() function to allow changing
vma->vm_file with the necessary refcount dance.

v2: add more users of this.
v3: add missing EXPORT_SYMBOL, rebase on mmap cleanup,
    add comments why we drop the reference on two occasions.
v4: make it clear that changing an anonymous vma is illegal.
v5: move vma_set_file to mm/util.c

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch> (v2)
Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>
Acked-by: Andrew Morton <akpm@linux-foundation.org>
Link: https://patchwork.freedesktop.org/patch/399360/

6 files changed, 8 insertions, 14 deletions

diff --git a/drivers/gpu/drm/etnaviv/etnaviv_gem.c b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
index bbd235473645..6d38c5c17f23 100644
--- a/drivers/gpu/drm/etnaviv/etnaviv_gem.c
+++ b/drivers/gpu/drm/etnaviv/etnaviv_gem.c
@@ -145,10 +145,8 @@ static int etnaviv_gem_mmap_obj(struct etnaviv_gem_object *etnaviv_obj,
 		 * address_space (so unmap_mapping_range does what we want,
 		 * in particular in the case of mmap'd dmabufs)
 		 */
-		fput(vma->vm_file);
-		get_file(etnaviv_obj->base.filp);
 		vma->vm_pgoff = 0;
-		vma->vm_file  = etnaviv_obj->base.filp;
+		vma_set_file(vma, etnaviv_obj->base.filp);
 
 		vma->vm_page_prot = vm_page_prot;
 	}
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
index 0dd477e56573..04e9c04545ad 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_dmabuf.c
@@ -114,8 +114,7 @@ static int i915_gem_dmabuf_mmap(struct dma_buf *dma_buf, struct vm_area_struct *
 	if (ret)
 		return ret;
 
-	fput(vma->vm_file);
-	vma->vm_file = get_file(obj->base.filp);
+	vma_set_file(vma, obj->base.filp);
 
 	return 0;
 }
diff --git a/drivers/gpu/drm/i915/gem/i915_gem_mman.c b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
index 3d69e51f3e4d..ec28a6cde49b 100644
--- a/drivers/gpu/drm/i915/gem/i915_gem_mman.c
+++ b/drivers/gpu/drm/i915/gem/i915_gem_mman.c
@@ -893,8 +893,9 @@ int i915_gem_mmap(struct file *filp, struct vm_area_struct *vma)
 	 * requires avoiding extraneous references to their filp, hence why
 	 * we prefer to use an anonymous file for their mmaps.
 	 */
-	fput(vma->vm_file);
-	vma->vm_file = anon;
+	vma_set_file(vma, anon);
+	/* Drop the initial creation reference, the vma is now holding one. */
+	fput(anon);
 
 	switch (mmo->mmap_type) {
 	case I915_MMAP_TYPE_WC:
diff --git a/drivers/gpu/drm/msm/msm_gem.c b/drivers/gpu/drm/msm/msm_gem.c
index 2e1bce7c0b19..311721ceee50 100644
--- a/drivers/gpu/drm/msm/msm_gem.c
+++ b/drivers/gpu/drm/msm/msm_gem.c
@@ -212,10 +212,8 @@ int msm_gem_mmap_obj(struct drm_gem_object *obj,
 		 * address_space (so unmap_mapping_range does what we want,
 		 * in particular in the case of mmap'd dmabufs)
 		 */
-		fput(vma->vm_file);
-		get_file(obj->filp);
 		vma->vm_pgoff = 0;
-		vma->vm_file  = obj->filp;
+		vma_set_file(vma, obj->filp);
 
 		vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
 	}
diff --git a/drivers/gpu/drm/omapdrm/omap_gem.c b/drivers/gpu/drm/omapdrm/omap_gem.c
index 68c271f4250b..30d299ca8795 100644
--- a/drivers/gpu/drm/omapdrm/omap_gem.c
+++ b/drivers/gpu/drm/omapdrm/omap_gem.c
@@ -564,9 +564,8 @@ int omap_gem_mmap_obj(struct drm_gem_object *obj,
 		 * address_space (so unmap_mapping_range does what we want,
 		 * in particular in the case of mmap'd dmabufs)
 		 */
-		fput(vma->vm_file);
 		vma->vm_pgoff = 0;
-		vma->vm_file  = get_file(obj->filp);
+		vma_set_file(vma, obj->filp);
 
 		vma->vm_page_prot = vm_get_page_prot(vma->vm_flags);
 	}
diff --git a/drivers/gpu/drm/vgem/vgem_drv.c b/drivers/gpu/drm/vgem/vgem_drv.c
index 9a413091abb6..f8635ccaf9a1 100644
--- a/drivers/gpu/drm/vgem/vgem_drv.c
+++ b/drivers/gpu/drm/vgem/vgem_drv.c
@@ -403,8 +403,7 @@ static int vgem_prime_mmap(struct drm_gem_object *obj,
 	if (ret)
 		return ret;
 
-	fput(vma->vm_file);
-	vma->vm_file = get_file(obj->filp);
+	vma_set_file(vma, obj->filp);
 	vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP;
 	vma->vm_page_prot = pgprot_writecombine(vm_get_page_prot(vma->vm_flags));