linux-kernel - Re: [mmotm] "x86/atomic: move __arch_atomic_add

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Date:   Thu, 16 Mar 2017 11:45:29 -0700
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     Andi Kleen <ak@...ux.intel.com>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        20170315021431.13107-3-andi@...stfloor.org,
        Ingo Molnar <mingo@...e.hu>,
        Thomas Gleixner <tglx@...utronix.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "x86@...nel.org" <x86@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [mmotm] "x86/atomic: move __arch_atomic_add_unless out of line"
 build error

On Thu, 16 Mar 2017 09:41:10 -0700 Andi Kleen <ak@...ux.intel.com> wrote:

> > Andi, why did you completely remove __arch_atomic_add_unless() from
> > the header? Don't we need at least a declaration there?
> 
> Actually it's there in my git version:
> 
> I wonder where it disappeared.
> 
> -/**
> - * __atomic_add_unless - add unless the number is already a given value
> - * @v: pointer of type atomic_t
> - * @a: the amount to add to v...
> - * @u: ...unless v is equal to u.
> - *
> - * Atomically adds @a to @v, so long as @v was not already @u.
> - * Returns the old value of @v.
> - */
> -static __always_inline int __atomic_add_unless(atomic_t *v, int a, int u)
> -{
> -       int c, old;
> -       c = atomic_read(v);
> -       for (;;) {
> -               if (unlikely(c == (u)))
> -                       break;
> -               old = atomic_cmpxchg((v), c, c + (a));
> -               if (likely(old == c))
> -                       break;
> -               c = old;
> -       }
> -       return c;
> -}
> +int __atomic_add_unless(atomic_t *v, int a, int u);

That was me fixing rejects (from
asm-generic-x86-wrap-atomic-operations.patch), incompletely.

--- a/arch/x86/include/asm/atomic.h~x86-atomic-move-__atomic_add_unless-out-of-line-fix
+++ a/arch/x86/include/asm/atomic.h
@@ -235,6 +235,8 @@ ATOMIC_OPS(xor, ^)
 #undef ATOMIC_FETCH_OP
 #undef ATOMIC_OP
 
+int __arch_atomic_add_unless(atomic_t *v, int a, int u);
+
 /**
  * arch_atomic_inc_short - increment of a short integer
  * @v: pointer to type int