linux-kernel - Re: [RFC 0/2] refcount: attempt to avoid imbalance warnings

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Date:   Fri, 1 Jul 2022 10:47:49 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Alexander Aring <aahringo@...hat.com>,
        Will Deacon <will@...nel.org>,
        Boqun Feng <boqun.feng@...il.com>,
        Mark Rutland <mark.rutland@....com>,
        thunder.leizhen@...wei.com, jacob.e.keller@...el.com,
        Andrew Morton <akpm@...ux-foundation.org>,
        Sparse Mailing-list <linux-sparse@...r.kernel.org>,
        cluster-devel <cluster-devel@...hat.com>,
        Luc Van Oostenryck <luc.vanoostenryck@...il.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC 0/2] refcount: attempt to avoid imbalance warnings

On Thu, Jun 30, 2022 at 09:34:10AM -0700, Linus Torvalds wrote:

Not commenting on sparse, since I'm not much qualified there, however,

>  include/linux/compiler_types.h | 2 ++
>  include/linux/refcount.h       | 6 +++---
>  2 files changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/include/linux/compiler_types.h b/include/linux/compiler_types.h
> index d08dfcb0ac68..4f2a819fd60a 100644
> --- a/include/linux/compiler_types.h
> +++ b/include/linux/compiler_types.h
> @@ -24,6 +24,7 @@ static inline void __chk_io_ptr(const volatile void __iomem *ptr) { }
>  /* context/locking */
>  # define __must_hold(x)	__attribute__((context(x,1,1)))
>  # define __acquires(x)	__attribute__((context(x,0,1)))
> +# define __cond_acquires(x) __attribute__((context(x,0,-1)))
>  # define __releases(x)	__attribute__((context(x,1,0)))
>  # define __acquire(x)	__context__(x,1)
>  # define __release(x)	__context__(x,-1)
> @@ -50,6 +51,7 @@ static inline void __chk_io_ptr(const volatile void __iomem *ptr) { }
>  /* context/locking */
>  # define __must_hold(x)
>  # define __acquires(x)
> +# define __cond_acquires(x)
>  # define __releases(x)
>  # define __acquire(x)	(void)0
>  # define __release(x)	(void)0
> diff --git a/include/linux/refcount.h b/include/linux/refcount.h
> index b8a6e387f8f9..a62fcca97486 100644
> --- a/include/linux/refcount.h
> +++ b/include/linux/refcount.h
> @@ -361,9 +361,9 @@ static inline void refcount_dec(refcount_t *r)
>  
>  extern __must_check bool refcount_dec_if_one(refcount_t *r);
>  extern __must_check bool refcount_dec_not_one(refcount_t *r);
> -extern __must_check bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock);
> -extern __must_check bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock);
> +extern __must_check bool refcount_dec_and_mutex_lock(refcount_t *r, struct mutex *lock) __cond_acquires(lock);
> +extern __must_check bool refcount_dec_and_lock(refcount_t *r, spinlock_t *lock) __cond_acquires(lock);
>  extern __must_check bool refcount_dec_and_lock_irqsave(refcount_t *r,
>  						       spinlock_t *lock,
> -						       unsigned long *flags);
> +						       unsigned long *flags) __cond_acquires(lock);
>  #endif /* _LINUX_REFCOUNT_H */


YES!, thank you!