[PATCH v3 8/9] kernel: export task_work_add
Daniel Vetter
daniel at ffwll.ch
Wed Aug 18 11:06:36 UTC 2021
On Wed, Aug 18, 2021 at 03:38:23PM +0800, Desmond Cheong Zhi Xi wrote:
> The task_work_add function is needed to prevent userspace races with
> DRM modesetting rights.
>
> Some DRM ioctls can change modesetting permissions while other
> concurrent users are performing modesetting. To prevent races with
> userspace, such functions should flush readers of old permissions
> before returning to user mode. As the function that changes
> permissions might itself be a reader of the old permissions, we intend
> to schedule this flush using task_work_add.
>
> However, when DRM is compiled as a loadable kernel module without
> exporting task_work_add, we get the following compilation error:
>
> ERROR: modpost: "task_work_add" [drivers/gpu/drm/drm.ko] undefined!
>
> Reported-by: kernel test robot <lkp at intel.com>
> Signed-off-by: Desmond Cheong Zhi Xi <desmondcheongzx at gmail.com>
Just realized another benefit of pushing the dev->master_rwsem write
locks down into ioctls that need them: We wouldn't need this function here
exported for use in drm. But also I'm not sure that works any better than
the design in your current patch set ...
-Daniel
> ---
> kernel/task_work.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/kernel/task_work.c b/kernel/task_work.c
> index 1698fbe6f0e1..90000404af2b 100644
> --- a/kernel/task_work.c
> +++ b/kernel/task_work.c
> @@ -60,6 +60,7 @@ int task_work_add(struct task_struct *task, struct callback_head *work,
>
> return 0;
> }
> +EXPORT_SYMBOL(task_work_add);
>
> /**
> * task_work_cancel_match - cancel a pending work added by task_work_add()
> --
> 2.25.1
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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