linux-kernel - Re: [PATCH] locking/atomics: Simplify the op definitions in atomic.h some more

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Date:   Sun, 6 May 2018 16:57:27 +0200
From:   Ingo Molnar <mingo@...nel.org>
To:     Andrea Parri <andrea.parri@...rulasolutions.com>
Cc:     Mark Rutland <mark.rutland@....com>,
        Peter Zijlstra <peterz@...radead.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        aryabinin@...tuozzo.com, boqun.feng@...il.com,
        catalin.marinas@....com, dvyukov@...gle.com, will.deacon@....com,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Paul E. McKenney" <paulmck@...ibm.com>,
        Peter Zijlstra <a.p.zijlstra@...llo.nl>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] locking/atomics: Simplify the op definitions in atomic.h
 some more


* Andrea Parri <andrea.parri@...rulasolutions.com> wrote:

> Hi Ingo,
> 
> > From 5affbf7e91901143f84f1b2ca64f4afe70e210fd Mon Sep 17 00:00:00 2001
> > From: Ingo Molnar <mingo@...nel.org>
> > Date: Sat, 5 May 2018 10:23:23 +0200
> > Subject: [PATCH] locking/atomics: Simplify the op definitions in atomic.h some more
> > 
> > Before:
> > 
> >  #ifndef atomic_fetch_dec_relaxed
> >  # ifndef atomic_fetch_dec
> >  #  define atomic_fetch_dec(v)			atomic_fetch_sub(1, (v))
> >  #  define atomic_fetch_dec_relaxed(v)		atomic_fetch_sub_relaxed(1, (v))
> >  #  define atomic_fetch_dec_acquire(v)		atomic_fetch_sub_acquire(1, (v))
> >  #  define atomic_fetch_dec_release(v)		atomic_fetch_sub_release(1, (v))
> >  # else
> >  #  define atomic_fetch_dec_relaxed		atomic_fetch_dec
> >  #  define atomic_fetch_dec_acquire		atomic_fetch_dec
> >  #  define atomic_fetch_dec_release		atomic_fetch_dec
> >  # endif
> >  #else
> >  # ifndef atomic_fetch_dec_acquire
> >  #  define atomic_fetch_dec_acquire(...)	__atomic_op_acquire(atomic_fetch_dec, __VA_ARGS__)
> >  # endif
> >  # ifndef atomic_fetch_dec_release
> >  #  define atomic_fetch_dec_release(...)	__atomic_op_release(atomic_fetch_dec, __VA_ARGS__)
> >  # endif
> >  # ifndef atomic_fetch_dec
> >  #  define atomic_fetch_dec(...)		__atomic_op_fence(atomic_fetch_dec, __VA_ARGS__)
> >  # endif
> >  #endif
> > 
> > After:
> > 
> >  #ifndef atomic_fetch_dec_relaxed
> >  # ifndef atomic_fetch_dec
> >  #  define atomic_fetch_dec(v)			atomic_fetch_sub(1, (v))
> >  #  define atomic_fetch_dec_relaxed(v)		atomic_fetch_sub_relaxed(1, (v))
> >  #  define atomic_fetch_dec_acquire(v)		atomic_fetch_sub_acquire(1, (v))
> >  #  define atomic_fetch_dec_release(v)		atomic_fetch_sub_release(1, (v))
> >  # else
> >  #  define atomic_fetch_dec_relaxed		atomic_fetch_dec
> >  #  define atomic_fetch_dec_acquire		atomic_fetch_dec
> >  #  define atomic_fetch_dec_release		atomic_fetch_dec
> >  # endif
> >  #else
> >  # ifndef atomic_fetch_dec
> >  #  define atomic_fetch_dec(...)		__atomic_op_fence(atomic_fetch_dec, __VA_ARGS__)
> >  #  define atomic_fetch_dec_acquire(...)	__atomic_op_acquire(atomic_fetch_dec, __VA_ARGS__)
> >  #  define atomic_fetch_dec_release(...)	__atomic_op_release(atomic_fetch_dec, __VA_ARGS__)
> >  # endif
> >  #endif
> > 
> > The idea is that because we already group these APIs by certain defines
> > such as atomic_fetch_dec_relaxed and atomic_fetch_dec in the primary
> > branches - we can do the same in the secondary branch as well.
> > 
> > ( Also remove some unnecessarily duplicate comments, as the API
> >   group defines are now pretty much self-documenting. )
> > 
> > No change in functionality.
> > 
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Linus Torvalds <torvalds@...ux-foundation.org>
> > Cc: Andrew Morton <akpm@...ux-foundation.org>
> > Cc: Thomas Gleixner <tglx@...utronix.de>
> > Cc: Paul E. McKenney <paulmck@...ux.vnet.ibm.com>
> > Cc: Will Deacon <will.deacon@....com>
> > Cc: linux-kernel@...r.kernel.org
> > Signed-off-by: Ingo Molnar <mingo@...nel.org>
> 
> This breaks compilation on RISC-V. (For some of its atomics, the arch
> currently defines the _relaxed and the full variants and it relies on
> the generic definitions for the _acquire and the _release variants.)

I don't have cross-compilation for RISC-V, which is a relatively new arch.
(Is there any RISC-V set of cross-compilation tools on kernel.org somewhere?)

Could you please send a patch that defines those variants against Linus's tree, 
like the PowerPC patch that does something similar:

  0476a632cb3a: locking/atomics/powerpc: Move cmpxchg helpers to asm/cmpxchg.h and define the full set of cmpxchg APIs

?

... and I'll integrate it into the proper place to make it all bisectable, etc.

Thanks,

	Ingo