linux-kernel - Re: [PATCH] locking/mutex: initialize osq lock in __MUTEX

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Date:   Mon, 29 Mar 2021 15:50:56 +0100
From:   Will Deacon <will@...nel.org>
To:     Nikitas Angelinas <nikitas.angelinas@...il.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] locking/mutex: initialize osq lock in
 __MUTEX_INITIALIZER()

On Mon, Mar 29, 2021 at 12:15:16AM -0700, Nikitas Angelinas wrote:
> Since __MUTEX_INITIALIZER() is used on memory that is initialized to 0
> anyway this change should not have an effect, but it seems better to
> initialize osq explicitly for completeness, as done in other macros and
> functions that initialize mutex and rwsem.
> 
> Signed-off-by: Nikitas Angelinas <nikitas.angelinas@...il.com>
> ---
>  include/linux/mutex.h | 8 ++++++++
>  1 file changed, 8 insertions(+)
> 
> diff --git a/include/linux/mutex.h b/include/linux/mutex.h
> index 515cff7..bff47f8 100644
> --- a/include/linux/mutex.h
> +++ b/include/linux/mutex.h
> @@ -129,10 +129,18 @@ do {									\
>  # define __DEP_MAP_MUTEX_INITIALIZER(lockname)
>  #endif
>  
> +#ifdef CONFIG_MUTEX_SPIN_ON_OWNER
> +# define __OSQ_MUTEX_INITIALIZER(lockname)			\
> +		, .osq = OSQ_LOCK_UNLOCKED
> +#else
> +# define __OSQ_MUTEX_INITIALIZER(lockname)
> +#endif
> +
>  #define __MUTEX_INITIALIZER(lockname) \
>  		{ .owner = ATOMIC_LONG_INIT(0) \
>  		, .wait_lock = __SPIN_LOCK_UNLOCKED(lockname.wait_lock) \
>  		, .wait_list = LIST_HEAD_INIT(lockname.wait_list) \
> +		__OSQ_MUTEX_INITIALIZER(lockname) \

You don't need the lockname parameter for this macro.

Will