Re: [PATCH 2/2] uaccess: minimize INLINE_COPY_USER-related ifdefery

[Yury Norov]

On Thu, Mar 26, 2026 at 03:15:09PM +0100, Christophe Leroy (CS GROUP) wrote:
> 
> 
> Le 25/03/2026 à 17:33, Yury Norov a écrit :
> > Now that we've got the same knob selecting inline vs outline copy_to_user()
> > and copy_from_user(), we can simplify the corresponding logic in the
> > uaccess.h.
> 
> I think we should get rid of ifdefery completly, see below. And with comment
> to previous patch,
> 
>     __is_defined(INLINE_COPY_TO_USER)
> 
> becomes
> 
>     !IS_ENABLED(CONFIG_ARCH_WANT_OUTLINE_USER_COPY)

It's out of the scope of the series. Feel free to submit a follow-up.

> diff --git a/include/linux/uaccess.h b/include/linux/uaccess.h
> index 327f967a24b8..02a05dd61a77 100644
> --- a/include/linux/uaccess.h
> +++ b/include/linux/uaccess.h
> @@ -190,10 +190,9 @@ _inline_copy_from_user(void *to, const void __user
> *from, unsigned long n)
>  	memset(to + (n - res), 0, res);
>  	return res;
>  }
> -#ifndef INLINE_COPY_FROM_USER
> +
>  extern __must_check unsigned long
>  _copy_from_user(void *, const void __user *, unsigned long);
> -#endif
> 
>  static inline __must_check unsigned long
>  _inline_copy_to_user(void __user *to, const void *from, unsigned long n)
> @@ -207,21 +206,19 @@ _inline_copy_to_user(void __user *to, const void
> *from, unsigned long n)
>  	}
>  	return n;
>  }
> -#ifndef INLINE_COPY_TO_USER
> +
>  extern __must_check unsigned long
>  _copy_to_user(void __user *, const void *, unsigned long);
> -#endif

This declares a function that may have no implementation. It's wrong.

>  static __always_inline unsigned long __must_check
>  copy_from_user_common(void *to, const void __user *from, unsigned long n,
> bool partial)
>  {
>  	if (!check_copy_size(to, n, false))
>  		return n;
> -#ifdef INLINE_COPY_FROM_USER
> -	return _inline_copy_from_user(to, from, n);
> -#else
> -	return _copy_from_user(to, from, n);
> -#endif
> +	if (__is_defined(INLINE_COPY_FROM_USER))
> +		return _inline_copy_from_user(to, from, n);
> +	else
> +		return _copy_from_user(to, from, n);

To me, this is just another form of ifdefery. I prefer to minimize the
number of IS_DEFINED() blocks, just as #ifdef. But it's maybe just me.

Let's merge INLINE_COPY_USER series, and then see how you follow up
would look?

>  }
> 
>  static __always_inline unsigned long __must_check
> @@ -242,11 +239,10 @@ copy_to_user_common(void __user *to, const void *from,
> unsigned long n, bool par
>  	if (!check_copy_size(from, n, true))
>  		return n;
> 
> -#ifdef INLINE_COPY_TO_USER
> -	return _inline_copy_to_user(to, from, n);
> -#else
> -	return _copy_to_user(to, from, n);
> -#endif
> +	if (__is_defined(INLINE_COPY_TO_USER))
> +		return _inline_copy_to_user(to, from, n);
> +	else
> +		return _copy_to_user(to, from, n);
>  }
> 
>  static __always_inline unsigned long __must_check
> 
> 
> Christophe