linux-kernel - Re: [PATCH 6/9] asm-generic/bitops/atomic.h: Rewrite using atomic_fetch

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Message-ID: <20180524124734.GE8689@arm.com>
Date:   Thu, 24 May 2018 13:47:39 +0100
From:   Will Deacon <will.deacon@....com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     linux-kernel@...r.kernel.org, mingo@...nel.org,
        linux-arm-kernel@...ts.infradead.org, yamada.masahiro@...ionext.com
Subject: Re: [PATCH 6/9] asm-generic/bitops/atomic.h: Rewrite using
 atomic_fetch_*

On Thu, May 24, 2018 at 02:44:10PM +0200, Peter Zijlstra wrote:
> On Thu, May 24, 2018 at 11:59:43AM +0100, Will Deacon wrote:
> > +static inline void set_bit(unsigned int nr, volatile unsigned long *p)
> >  {
> > +	p += BIT_WORD(nr);
> > +	atomic_long_fetch_or_relaxed(BIT_MASK(nr), (atomic_long_t *)p);
> >  }
> >  
> > +static inline void clear_bit(unsigned int nr, volatile unsigned long *p)
> >  {
> > +	p += BIT_WORD(nr);
> > +	atomic_long_fetch_andnot_relaxed(BIT_MASK(nr), (atomic_long_t *)p);
> >  }
> >  
> > +static inline void change_bit(unsigned int nr, volatile unsigned long *p)
> >  {
> > +	p += BIT_WORD(nr);
> > +	atomic_long_fetch_xor_relaxed(BIT_MASK(nr), (atomic_long_t *)p);
> >  }
> 
> Why use the fetch variants here?

I noticed the same thing just now; I'll drop that and just use the
non-value-returning variants. It's shame that I can't do the same for
the lock.h unlock code, but we don't have non-returning release variants.

Will