linux-kernel - Re: [PATCH 3/5] seqlock: introduce seqprop

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Date:   Fri, 15 Sep 2023 20:25:31 +0200
From:   Alexey Gladkov <legion@...nel.org>
To:     Oleg Nesterov <oleg@...hat.com>
Cc:     Boqun Feng <boqun.feng@...il.com>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Rik van Riel <riel@...riel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Waiman Long <longman@...hat.com>,
        Will Deacon <will@...nel.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/5] seqlock: introduce seqprop_lock/unlock

On Wed, Sep 13, 2023 at 05:50:00PM +0200, Oleg Nesterov wrote:
> which can be used to take/release the corresponding lock.
> 
> Thanks to the previous patch, it is trivial to pass 2 arguments to
> the new __seqprop_##lockname##_lock/unlock "methods", plus we do not
> loose the type info and thus the new seqprop's are "type safe".
> 
> So for example
> 
> 	void func(seqcount_rwlock_t *s, rwlock_t *l)
> 	{
> 		seqprop_lock(s, l);
> 	}
> 
> happily compiles, but this one
> 
> 	void func(seqcount_rwlock_t *s, spinlock_t *l)
> 	{
> 		seqprop_lock(s, l);
> 	}
> 
> doesn't.
> 
> Signed-off-by: Oleg Nesterov <oleg@...hat.com>
> ---
>  include/linux/seqlock.h | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
> index 41e36f8afad4..9831683a0102 100644
> --- a/include/linux/seqlock.h
> +++ b/include/linux/seqlock.h
> @@ -241,6 +241,21 @@ static __always_inline void						\
>  __seqprop_##lockname##_assert(const seqcount_##lockname##_t *s)		\
>  {									\
>  	__SEQ_LOCK(lockdep_assert_held(s->lock));			\
> +}									\
> +									\
> +static __always_inline void						\
> +__seqprop_##lockname##_lock(seqcount_##lockname##_t *s,			\
> +				locktype *lock)				\
> +{									\
> +	__SEQ_LOCK(WARN_ON_ONCE(s->lock != lock));			\
> +	lockbase##_lock(lock);						\
> +}									\
> +									\
> +static __always_inline void						\
> +__seqprop_##lockname##_unlock(seqcount_##lockname##_t *s,		\
> +				locktype *lock)				\
> +{									\
> +	lockbase##_unlock(lock); 					\
>  }

Why are you creating a new method with an unused argument s ?

>  
>  /*
> @@ -306,6 +321,12 @@ SEQCOUNT_LOCKNAME(mutex,        struct mutex,    true,     mutex)
>  #define seqprop_preemptible(s)		__seqprop(s, preemptible)(s)
>  #define seqprop_assert(s)		__seqprop(s, assert)(s)
>  
> +/* seqcount_t doesn't have these methods */
> +static inline void __seqprop_lock   (seqcount_t *s, void *l) { BUILD_BUG(); }
> +static inline void __seqprop_unlock (seqcount_t *s, void *l) { BUILD_BUG(); }
> +#define seqprop_lock(s, l)		__seqprop(s, lock)(s, l)
> +#define seqprop_unlock(s, l)		__seqprop(s, unlock)(s, l)
> +
>  /**
>   * __read_seqcount_begin() - begin a seqcount_t read section w/o barrier
>   * @s: Pointer to seqcount_t or any of the seqcount_LOCKNAME_t variants
> -- 
> 2.25.1.362.g51ebf55
> 

-- 
Rgrds, legion