From 72d8d2bd915c947f76b54d640963a805dcb5cf97 Mon Sep 17 00:00:00 2001 From: Rob Clark Date: Wed, 30 Nov 2022 10:57:48 -0800 Subject: [PATCH] drm/shmem-helper: Avoid vm_open error paths commit 09bf649a74573cb596e211418a4f8008f265c5a9 upstream. vm_open() is not allowed to fail. Fortunately we are guaranteed that the pages are already pinned, thanks to the initial mmap which is now being cloned into a forked process, and only need to increment the refcnt. So just increment it directly. Previously if a signal was delivered at the wrong time to the forking process, the mutex_lock_interruptible() could fail resulting in the pages_use_count not being incremented. Fixes: 2194a63a818d ("drm: Add library for shmem backed GEM objects") Cc: stable@vger.kernel.org Signed-off-by: Rob Clark Reviewed-by: Daniel Vetter Signed-off-by: Javier Martinez Canillas Link: https://patchwork.freedesktop.org/patch/msgid/20221130185748.357410-3-robdclark@gmail.com Signed-off-by: Greg Kroah-Hartman (cherry picked from commit 1074fefce9cc6730fe5f602c0287850c2698e315) Signed-off-by: Thomas Lamprecht --- drivers/gpu/drm/drm_gem_shmem_helper.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) diff --git a/drivers/gpu/drm/drm_gem_shmem_helper.c b/drivers/gpu/drm/drm_gem_shmem_helper.c index 808d364a5544..15c3849e995b 100644 --- a/drivers/gpu/drm/drm_gem_shmem_helper.c +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c @@ -541,12 +541,20 @@ static void drm_gem_shmem_vm_open(struct vm_area_struct *vma) { struct drm_gem_object *obj = vma->vm_private_data; struct drm_gem_shmem_object *shmem = to_drm_gem_shmem_obj(obj); - int ret; WARN_ON(shmem->base.import_attach); - ret = drm_gem_shmem_get_pages(shmem); - WARN_ON_ONCE(ret != 0); + mutex_lock(&shmem->pages_lock); + + /* + * We should have already pinned the pages when the buffer was first + * mmap'd, vm_open() just grabs an additional reference for the new + * mm the vma is getting copied into (ie. on fork()). + */ + if (!WARN_ON_ONCE(!shmem->pages_use_count)) + shmem->pages_use_count++; + + mutex_unlock(&shmem->pages_lock); drm_gem_vm_open(vma); } -- 2.39.2