linux-kernel - Re: locking/atomic: Introduce atomic_try

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Message-ID: <20170324180441.gj5uhlttdzt7zxod@hirez.programming.kicks-ass.net>
Date:   Fri, 24 Mar 2017 19:04:41 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Paul McKenney <paulmck@...ux.vnet.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: locking/atomic: Introduce atomic_try_cmpxchg()

On Fri, Mar 24, 2017 at 07:00:25PM +0100, Peter Zijlstra wrote:
> static inline bool try_cmpxchg2(unsigned int *ptr, unsigned int *val, unsigned int new)
> {
> 	unsigned int old = *val;
> 	bool success;
> 
>         asm volatile goto("lock cmpxchgl %[new], %[ptr]; "
>                           "jnz %[label]"
>                      : /* no output */
>                      : [ptr] "+m" (*ptr),
>                        [old] "+a" (old)
>                        [new] "r" (new)
>                      : "memory"
>                      : label);
>         return 1;
> 
> label:
> 	*val = old;
> 	return 0;
> }

N/m, I'm apparently so tired I didn't see the compiler errors :/