linux-kernel - Re: [RFC][PATCH 1/4] compiler-context-analysys: Add __cond

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Message-ID: <CANpmjNP0u47EfcVa+WaicLBpvqhW47JCPQ5ENwh33QUWpN5=bw@mail.gmail.com>
Date: Wed, 21 Jan 2026 14:09:33 +0100
From: Marco Elver <elver@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>
Cc: linux-kernel@...r.kernel.org, bigeasy@...utronix.de, mingo@...nel.org, 
	tglx@...utronix.de, will@...nel.org, boqun.feng@...il.com, longman@...hat.com, 
	hch@....de, rostedt@...dmis.org, bvanassche@....org, llvm@...ts.linux.dev
Subject: Re: [RFC][PATCH 1/4] compiler-context-analysys: Add __cond_releases()

On Wed, 21 Jan 2026 at 12:13, Peter Zijlstra <peterz@...radead.org> wrote:
>
> Useful for things like unlock fastpaths, which on success release the
> lock.
>
> Suggested-by: Marco Elver <elver@...gle.com>
> Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>

Reviewed-by: Marco Elver <elver@...gle.com>

> ---
>  include/linux/compiler-context-analysis.h |   32 ++++++++++++++++++++++++++++++
>  1 file changed, 32 insertions(+)
>
> --- a/include/linux/compiler-context-analysis.h
> +++ b/include/linux/compiler-context-analysis.h
> @@ -320,6 +320,38 @@ static inline void _context_unsafe_alias
>   */
>  #define __releases(...)                __releases_ctx_lock(__VA_ARGS__)
>
> +/*
> + * Clang's analysis does not care precisely about the value, only that it is
> + * either zero or non-zero. So the __cond_acquires() interface might be
> + * misleading if we say that @ret is the value returned if acquired. Instead,
> + * provide symbolic variants which we translate.
> + */
> +#define __cond_acquires_impl_not_true(x, ...)     __try_acquires##__VA_ARGS__##_ctx_lock(0, x)
> +#define __cond_acquires_impl_not_false(x, ...)    __try_acquires##__VA_ARGS__##_ctx_lock(1, x)
> +#define __cond_acquires_impl_not_nonzero(x, ...)  __try_acquires##__VA_ARGS__##_ctx_lock(0, x)
> +#define __cond_acquires_impl_not_0(x, ...)        __try_acquires##__VA_ARGS__##_ctx_lock(1, x)
> +#define __cond_acquires_impl_not_nonnull(x, ...)  __try_acquires##__VA_ARGS__##_ctx_lock(0, x)
> +#define __cond_acquires_impl_not_NULL(x, ...)     __try_acquires##__VA_ARGS__##_ctx_lock(1, x)
> +
> +/**
> + * __cond_releases() - function attribute, function conditionally
> + *                     releases a context lock exclusively
> + * @ret: abstract value returned by function if context lock releases
> + * @x: context lock instance pointer
> + *
> + * Function attribute declaring that the function conditionally releases the
> + * given context lock instance @x exclusively. The associated context(s) must
> + * be active on entry. The function return value @ret denotes when the context
> + * lock is released.
> + *
> + * @ret may be one of: true, false, nonzero, 0, nonnull, NULL.
> + *
> + * NOTE: clang does not have a native attribute for this; instead implement
> + *       it as an unconditional release and a conditional acquire for the
> + *       inverted condition -- which is semantically equivalent.
> + */
> +#define __cond_releases(ret, x) __releases(x) __cond_acquires_impl_not_##ret(x)
> +
>  /**
>   * __acquire() - function to acquire context lock exclusively
>   * @x: context lock instance pointer
>
>