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

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Date:   Fri, 15 Sep 2023 20:43:35 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Alexey Gladkov <legion@...nel.org>
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 09/15, Alexey Gladkov wrote:
>
> On Wed, Sep 13, 2023 at 05:50:00PM +0200, Oleg Nesterov wrote:
> > +									\
> > +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 ?

To make it consistent/symmetrical with _lock() which does
__SEQ_LOCK(WARN_ON_ONCE(s->lock != lock)). _unlock() could do the
same check as well, but somehow I decided it would be too much.

And with other "methods". Say, __seqprop_##lockname##_preemptible(s)
doesn't use 's' too.

Otherwise they both do not need the 1st seqcount_##lockname##_t *s
argument.

Oleg.