Re: [patch V4 11/14] x86/vdso: Prepare for robust futex unlock support

[André Almeida]

Em 02/04/2026 12:21, Thomas Gleixner escreveu:
> There will be a VDSO function to unlock non-contended robust futexes in
> user space. The unlock sequence is racy vs. clearing the list_pending_op
> pointer in the task's robust list head. To plug this race the kernel needs
> to know the critical section window so it can clear the pointer when the
> task is interrupted within that race window. The window is determined by
> labels in the inline assembly.
>
> Add these symbols to the vdso2c generator and use them in the VDSO VMA code
> to update the critical section addresses in mm_struct::futex on (re)map().
>
> The symbols are not exported to user space, but available in the debug
> version of the vDSO.
>
> Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxx>

A left a minor nit bellow, but

Reviewed-by: André Almeida <andrealmeid@xxxxxxxxxx>

> ---
> V3: Rename the symbols once more
> V2: Rename the symbols
> ---

[...]

> @@ -80,6 +106,7 @@ static int vdso_mremap(const struct vm_s
>   
>   	vdso_fix_landing(image, new_vma);
>   	current->mm->context.vdso = (void __user *)new_vma->vm_start;
> +	vdso_futex_robust_unlock_update_ips();
>   
>   	return 0;
>   }
> @@ -189,6 +216,8 @@ static int map_vdso(const struct vdso_im
>   	current->mm->context.vdso = (void __user *)text_start;
>   	current->mm->context.vdso_image = image;
>   

No need for this empty space.

> +	vdso_futex_robust_unlock_update_ips();
> +
>   up_fail:
>   	mmap_write_unlock(mm);
>   	return ret;