Re: [PATCH] err.h: use __always_inline on all error pointer helpers

[Nathan Chancellor]

On Tue, May 26, 2026 at 12:18:41PM +0200, Arnd Bergmann wrote:
> From: Arnd Bergmann <arnd@xxxxxxxx>
> 
> While testing randconfig builds on s390, I came across a
> link failure with CONFIG_DMA_SHARED_BUFFER disabled:
> 
> ERROR: modpost: "dma_buf_put" [drivers/iommu/iommufd/iommufd.ko] undefined!
> 
> The problem here is that IS_ERR() is not inlined and dead code elimination
> fails as a consequence.
> 
> The err.h helpers all turn into a trivial assignment ot a bit mask
> and should never result in a function call, so force them to always be
> inline. This should generally result in better object code aside from
> avoiding the link failure above.
> 
> Signed-off-by: Arnd Bergmann <arnd@xxxxxxxx>

Yeah, seems reasonable to me. I agree that this should generally result
in better generated code as opposed to these helpers being generated out
of line.

Reviewed-by: Nathan Chancellor <nathan@xxxxxxxxxx>

> ---
>  include/linux/err.h | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/include/linux/err.h b/include/linux/err.h
> index 8c37be0620ab..d3e38d5b3a98 100644
> --- a/include/linux/err.h
> +++ b/include/linux/err.h
> @@ -36,7 +36,7 @@
>   *
>   * Return: A pointer with @error encoded within its value.
>   */
> -static inline void * __must_check ERR_PTR(long error)
> +static __always_inline void * __must_check ERR_PTR(long error)
>  {
>  	return (void *) error;
>  }
> @@ -60,7 +60,7 @@ static inline void * __must_check ERR_PTR(long error)
>   * @ptr: An error pointer.
>   * Return: The error code within @ptr.
>   */
> -static inline long __must_check PTR_ERR(__force const void *ptr)
> +static __always_inline long __must_check PTR_ERR(__force const void *ptr)
>  {
>  	return (long) ptr;
>  }
> @@ -73,7 +73,7 @@ static inline long __must_check PTR_ERR(__force const void *ptr)
>   * @ptr: The pointer to check.
>   * Return: true if @ptr is an error pointer, false otherwise.
>   */
> -static inline bool __must_check IS_ERR(__force const void *ptr)
> +static __always_inline bool __must_check IS_ERR(__force const void *ptr)
>  {
>  	return IS_ERR_VALUE((unsigned long)ptr);
>  }
> @@ -87,7 +87,7 @@ static inline bool __must_check IS_ERR(__force const void *ptr)
>   *
>   * Like IS_ERR(), but also returns true for a null pointer.
>   */
> -static inline bool __must_check IS_ERR_OR_NULL(__force const void *ptr)
> +static __always_inline bool __must_check IS_ERR_OR_NULL(__force const void *ptr)
>  {
>  	return unlikely(!ptr) || IS_ERR_VALUE((unsigned long)ptr);
>  }
> @@ -99,7 +99,7 @@ static inline bool __must_check IS_ERR_OR_NULL(__force const void *ptr)
>   * Explicitly cast an error-valued pointer to another pointer type in such a
>   * way as to make it clear that's what's going on.
>   */
> -static inline void * __musggt_check ERR_CAST(__force const void *ptr)
> +static __always_inline void * __must_check ERR_CAST(__force const void *ptr)
>  {
>  	/* cast away the const */
>  	return (void *) ptr;
> @@ -122,7 +122,7 @@ static inline void * __must_check ERR_CAST(__force const void *ptr)
>   *
>   * Return: The error code within @ptr if it is an error pointer; 0 otherwise.
>   */
> -static inline int __must_check PTR_ERR_OR_ZERO(__force const void *ptr)
> +static __always_inline int __must_check PTR_ERR_OR_ZERO(__force const void *ptr)
>  {
>  	if (IS_ERR(ptr))
>  		return PTR_ERR(ptr);
> -- 
> 2.39.5
> 

-- 
Cheers,
Nathan