This is a note to let you know that I've just added the patch titled drm/shmem-helper: Avoid vm_open error paths to the 5.10-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: drm-shmem-helper-avoid-vm_open-error-paths.patch and it can be found in the queue-5.10 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. >From 09bf649a74573cb596e211418a4f8008f265c5a9 Mon Sep 17 00:00:00 2001 From: Rob Clark <robdclark@xxxxxxxxxxxx> Date: Wed, 30 Nov 2022 10:57:48 -0800 Subject: drm/shmem-helper: Avoid vm_open error paths From: Rob Clark <robdclark@xxxxxxxxxxxx> 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@xxxxxxxxxxxxxxx Signed-off-by: Rob Clark <robdclark@xxxxxxxxxxxx> Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx> Signed-off-by: Javier Martinez Canillas <javierm@xxxxxxxxxx> Link: https://patchwork.freedesktop.org/patch/msgid/20221130185748.357410-3-robdclark@xxxxxxxxx Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- drivers/gpu/drm/drm_gem_shmem_helper.c | 14 +++++++++++--- 1 file changed, 11 insertions(+), 3 deletions(-) --- a/drivers/gpu/drm/drm_gem_shmem_helper.c +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c @@ -563,12 +563,20 @@ static void drm_gem_shmem_vm_open(struct { 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); } Patches currently in stable-queue which might be from robdclark@xxxxxxxxxxxx are queue-5.10/drm-shmem-helper-remove-errant-put-in-error-path.patch queue-5.10/drm-shmem-helper-avoid-vm_open-error-paths.patch