Date:   Thu, 15 Jun 2023 07:07:22 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Mark Rutland <mark.rutland@....com>
Cc:     linux-kernel@...r.kernel.org, boqun.feng@...il.com,
        keescook@...omium.org, peterz@...radead.org, will@...nel.org
Subject: Re: [PATCH] locking/atomic: scripts: fix ${atomic}_dec_if_positive()
 kerneldoc

On Thu, Jun 15, 2023 at 02:27:34PM +0100, Mark Rutland wrote:
> The ${atomic}_dec_if_positive() ops are unlike all the other conditional
> atomic ops. Rather than returning a boolean success value, these return
> the value that the atomic variable would be updated to, even when no
> update is performed.
> 
> We missed this when adding kerneldoc comments, and the documentation for
> ${atomic}_dec_if_positive() erroneously states:
> 
> | Return: @true if @v was updated, @false otherwise.
> 
> Ideally we'd clean this up by aligning ${atomic}_dec_if_positive() with
> the usual atomic op conventions: with ${atomic}_fetch_dec_if_positive()
> for those who care about the value of the varaible, and
> ${atomic}_dec_if_positive() returning a boolean success value.
> 
> In the mean time, align the documentation with the current reality.
> 
> Fixes: ad8110706f381170 ("locking/atomic: scripts: generate kerneldoc comments")
> Signed-off-by: Mark Rutland <mark.rutland@....com>
> Cc: Boqun Feng <boqun.feng@...il.com>
> Cc: Kees Cook <keescook@...omium.org>
> Cc: Paul E. McKenney <paulmck@...nel.org>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Will Deacon <will@...nel.org>

Reviewed-by: Paul E. McKenney <paulmck@...nel.org>

> ---
>  include/linux/atomic/atomic-arch-fallback.h | 6 +++---
>  include/linux/atomic/atomic-instrumented.h  | 8 ++++----
>  include/linux/atomic/atomic-long.h          | 4 ++--
>  scripts/atomic/kerneldoc/dec_if_positive    | 2 +-
>  4 files changed, 10 insertions(+), 10 deletions(-)
> 
> diff --git a/include/linux/atomic/atomic-arch-fallback.h b/include/linux/atomic/atomic-arch-fallback.h
> index 8cded57dd7a6f..18f5744dfb5d8 100644
> --- a/include/linux/atomic/atomic-arch-fallback.h
> +++ b/include/linux/atomic/atomic-arch-fallback.h
> @@ -2520,7 +2520,7 @@ raw_atomic_dec_unless_positive(atomic_t *v)
>   *
>   * Safe to use in noinstr code; prefer atomic_dec_if_positive() elsewhere.
>   *
> - * Return: @true if @v was updated, @false otherwise.
> + * Return: The old value of (@v - 1), regardless of whether @v was updated.
>   */
>  static __always_inline int
>  raw_atomic_dec_if_positive(atomic_t *v)
> @@ -4636,7 +4636,7 @@ raw_atomic64_dec_unless_positive(atomic64_t *v)
>   *
>   * Safe to use in noinstr code; prefer atomic64_dec_if_positive() elsewhere.
>   *
> - * Return: @true if @v was updated, @false otherwise.
> + * Return: The old value of (@v - 1), regardless of whether @v was updated.
>   */
>  static __always_inline s64
>  raw_atomic64_dec_if_positive(atomic64_t *v)
> @@ -4657,4 +4657,4 @@ raw_atomic64_dec_if_positive(atomic64_t *v)
>  }
>  
>  #endif /* _LINUX_ATOMIC_FALLBACK_H */
> -// 3916f02c038baa3f5190d275f68b9211667fcc9d
> +// 202b45c7db600ce36198eb1f1fc2c2d5268ace2d
> diff --git a/include/linux/atomic/atomic-instrumented.h b/include/linux/atomic/atomic-instrumented.h
> index ebfc795f921b9..d401b406ef7c4 100644
> --- a/include/linux/atomic/atomic-instrumented.h
> +++ b/include/linux/atomic/atomic-instrumented.h
> @@ -1570,7 +1570,7 @@ atomic_dec_unless_positive(atomic_t *v)
>   *
>   * Unsafe to use in noinstr code; use raw_atomic_dec_if_positive() there.
>   *
> - * Return: @true if @v was updated, @false otherwise.
> + * Return: The old value of (@v - 1), regardless of whether @v was updated.
>   */
>  static __always_inline int
>  atomic_dec_if_positive(atomic_t *v)
> @@ -3134,7 +3134,7 @@ atomic64_dec_unless_positive(atomic64_t *v)
>   *
>   * Unsafe to use in noinstr code; use raw_atomic64_dec_if_positive() there.
>   *
> - * Return: @true if @v was updated, @false otherwise.
> + * Return: The old value of (@v - 1), regardless of whether @v was updated.
>   */
>  static __always_inline s64
>  atomic64_dec_if_positive(atomic64_t *v)
> @@ -4698,7 +4698,7 @@ atomic_long_dec_unless_positive(atomic_long_t *v)
>   *
>   * Unsafe to use in noinstr code; use raw_atomic_long_dec_if_positive() there.
>   *
> - * Return: @true if @v was updated, @false otherwise.
> + * Return: The old value of (@v - 1), regardless of whether @v was updated.
>   */
>  static __always_inline long
>  atomic_long_dec_if_positive(atomic_long_t *v)
> @@ -5000,4 +5000,4 @@ atomic_long_dec_if_positive(atomic_long_t *v)
>  
>  
>  #endif /* _LINUX_ATOMIC_INSTRUMENTED_H */
> -// 06cec02e676a484857aee38b0071a1d846ec9457
> +// 1568f875fef72097413caab8339120c065a39aa4
> diff --git a/include/linux/atomic/atomic-long.h b/include/linux/atomic/atomic-long.h
> index f6df2adadf997..c82947170ddc8 100644
> --- a/include/linux/atomic/atomic-long.h
> +++ b/include/linux/atomic/atomic-long.h
> @@ -1782,7 +1782,7 @@ raw_atomic_long_dec_unless_positive(atomic_long_t *v)
>   *
>   * Safe to use in noinstr code; prefer atomic_long_dec_if_positive() elsewhere.
>   *
> - * Return: @true if @v was updated, @false otherwise.
> + * Return: The old value of (@v - 1), regardless of whether @v was updated.
>   */
>  static __always_inline long
>  raw_atomic_long_dec_if_positive(atomic_long_t *v)
> @@ -1795,4 +1795,4 @@ raw_atomic_long_dec_if_positive(atomic_long_t *v)
>  }
>  
>  #endif /* _LINUX_ATOMIC_LONG_H */
> -// 029d2e3a493086671e874a4c2e0e42084be42403
> +// 4ef23f98c73cff96d239896175fd26b10b88899e
> diff --git a/scripts/atomic/kerneldoc/dec_if_positive b/scripts/atomic/kerneldoc/dec_if_positive
> index 7c742866fb6b6..04f1aed3cf830 100644
> --- a/scripts/atomic/kerneldoc/dec_if_positive
> +++ b/scripts/atomic/kerneldoc/dec_if_positive
> @@ -7,6 +7,6 @@ cat <<EOF
>   *
>   * ${desc_noinstr}
>   *
> - * Return: @true if @v was updated, @false otherwise.
> + * Return: The old value of (@v - 1), regardless of whether @v was updated.
>   */
>  EOF
> -- 
> 2.30.2
> 

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