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Date: Thu, 17 Jul 2014 19:44:41 -0400 From: Pranith Kumar <bobby.prani@...il.com> To: Christoph Lameter <cl@...two.org> CC: rdunlap@...radead.org, linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH v2 1/1] doc: Add remote CPU access details and others to this_cpu_ops.txt On 07/17/2014 11:19 AM, Christoph Lameter wrote: > Regarding atomic_t in per cpu areas: I am uncomfortable especially > because both locked and unlocked RMW write operations could be acting on > values in the same cacheline. I am concerned that the unlocked operation > could have an unpredictable result. > > > f.e. the following per cpu data structure > > struct test { > atomic_t a; > int b; > } onecacheline; > > > Local cpu does > > this_cpu_inc(onecacheline.b); > > If this is racing with a remote cpus: > > atomic_inc(percpu(&a, cpu)) > > then we have on x86 a increment operation with locked semantics racing > with an unlocked one on the same cacheline. > OK, I will add this as a warning in the documentation. Thanks! -- Pranith -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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