On Tue, Nov 29, 2022 at 12:02:42PM -0800, Rob Clark wrote:
> From: Rob Clark <robdclark@xxxxxxxxxxxx>
>
> vm_open() is not allowed to fail. Fortunately we are guaranteed that
> the pages are already pinned, and only need to increment the refcnt. So
> just increment it directly.
Please mention hare that the only issue is the mutex_lock_interruptible,
and the only way we've found to hit this is if you send a signal to the
original process in a fork() at _just_ the right time.
With that: Reviewed-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
>
> Fixes: 2194a63a818d ("drm: Add library for shmem backed GEM objects")
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Rob Clark <robdclark@xxxxxxxxxxxx>
> ---
> 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 110a9eac2af8..9885ba64127f 100644
> --- a/drivers/gpu/drm/drm_gem_shmem_helper.c
> +++ b/drivers/gpu/drm/drm_gem_shmem_helper.c
> @@ -571,12 +571,20 @@ 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, vm_open() just grabs
> + * an additional reference for the new mm the vma is getting
> + * copied into.
> + */
> + WARN_ON_ONCE(!shmem->pages_use_count);
> +
> + shmem->pages_use_count++;
> + mutex_unlock(&shmem->pages_lock);
>
> drm_gem_vm_open(vma);
> }
> --
> 2.38.1
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
