linux-kernel - Re: [PATCH v2 1/1] doc: Add remote CPU access details and others to this_cpu

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <alpine.DEB.2.11.1407171005450.28248@gentwo.org>
Date:	Thu, 17 Jul 2014 10:19:03 -0500 (CDT)
From:	Christoph Lameter <cl@...two.org>
To:	Pranith Kumar <bobby.prani@...il.com>
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

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.

--
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/