Messages in this thread | | | Date | Mon, 13 Dec 2021 11:59:48 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v2 3/9] atomic: Introduce atomic_{inc,dec,dec_and_test}_overflow() |
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On Mon, Dec 13, 2021 at 10:06:01AM +0000, Mark Rutland wrote: > On Fri, Dec 10, 2021 at 05:16:21PM +0100, Peter Zijlstra wrote:
> > +#ifndef arch_atomic_inc_overflow > > +#define arch_atomic_inc_overflow(_v, _label) \ > > +do { \ > > + int __old = arch_atomic_fetch_inc(_v); \ > > + if (unlikely(__old <= 0)) \ > > + goto _label; \ > > +} while (0) > > +#endif > > + > > +#ifndef arch_atomic_dec_overflow > > +#define arch_atomic_dec_overflow(_v, _label) \ > > +do { \ > > + int __new = arch_atomic_dec_return(_v); \ > > + if (unlikely(__new <= 0)) \ > > + goto _label; \ > > +} while (0) > > +#endif > > + > > +#ifndef arch_atomic_dec_and_test_overflow > > +#define arch_atomic_dec_and_test_overflow(_v, _label) \ > > +({ \ > > + bool __ret = false; \ > > + int __new = arch_atomic_dec_return(_v); \ > > + if (unlikely(__new < 0)) \ > > + goto _label; \ > > + if (unlikely(__new == 0)) \ > > + __ret = true; \ > > + __ret; \ > > +}) > > +#endif > > I had wanted to move at least part of this to a function to ensure > single-evaluation and avoid accidental symbol aliasing, but (as we discussed > over IRC) I couldn't find any good way to do so, and given this is sufficiently > specialise I think we should be ok with this as-is. It's certainly no worse > than the existing stuff for xchg/cmpxchg.
Right, as you know I tried the same :-) Anyway, the above macros should be free of multi-evaluation issues, both _v and _label are only used the once. Aliassing is always a possibility but minimized by __ prefixing the local variables.
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