linux-kernel - Re: [PATCH v4 08/16] locking/rwsem: Make rwsem_spin_on

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Message-ID: <20190417090006.GC4038@hirez.programming.kicks-ass.net>
Date:   Wed, 17 Apr 2019 11:00:06 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Waiman Long <longman@...hat.com>
Cc:     Ingo Molnar <mingo@...hat.com>, Will Deacon <will.deacon@....com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Davidlohr Bueso <dave@...olabs.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        huang ying <huang.ying.caritas@...il.com>
Subject: Re: [PATCH v4 08/16] locking/rwsem: Make rwsem_spin_on_owner()
 return owner state

On Sat, Apr 13, 2019 at 01:22:51PM -0400, Waiman Long wrote:
> This patch modifies rwsem_spin_on_owner() to return four possible
> values to better reflect the state of lock holder which enables us to
> make a better decision of what to do next.
> 
> In the special case that there is no active lock and the handoff bit
> is set, optimistic spinning has to be stopped.
> 
> Signed-off-by: Waiman Long <longman@...hat.com>
> ---
>  kernel/locking/rwsem.c | 45 +++++++++++++++++++++++++++++++++++-------
>  1 file changed, 38 insertions(+), 7 deletions(-)
> 
> diff --git a/kernel/locking/rwsem.c b/kernel/locking/rwsem.c
> index aaab546a890d..2d6850c3e77b 100644
> --- a/kernel/locking/rwsem.c
> +++ b/kernel/locking/rwsem.c
> @@ -156,6 +156,11 @@ static inline bool is_rwsem_owner_spinnable(struct task_struct *owner)
>  	return !((unsigned long)owner & RWSEM_ANONYMOUSLY_OWNED);
>  }
>  
> +static inline bool is_rwsem_owner_reader(struct task_struct *owner)
> +{
> +	return (unsigned long)owner & RWSEM_READER_OWNED;
> +}

Move this and the surrounding helpers into the RWSEM_SPIN_ON_OWNER
block, it is only used there and that way all the code is together.