linux-kernel - Re: ipc,sem: sysv semaphore scalability

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Message-ID: <CA+i8gKLSBddyPGL6FW63=wB68gmafaF24G3ZL7P+qyTw95nQHQ@mail.gmail.com>
Date:	Sun, 31 Mar 2013 09:38:24 +0700
From:	Emmanuel Benisty <benisty.e@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Davidlohr Bueso <davidlohr.bueso@...com>,
	Dave Jones <davej@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...riel.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	hhuang@...hat.com, "Low, Jason" <jason.low2@...com>,
	Michel Lespinasse <walken@...gle.com>,
	Larry Woodman <lwoodman@...hat.com>,
	"Vinod, Chegu" <chegu_vinod@...com>,
	Peter Hurley <peter@...leysoftware.com>
Subject: Re: ipc,sem: sysv semaphore scalability

Hi Linus,

On Sun, Mar 31, 2013 at 12:22 AM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Fri, Mar 29, 2013 at 10:57 PM, Emmanuel Benisty <benisty.e@...il.com> wrote:
>> On Sat, Mar 30, 2013 at 12:10 PM, Linus Torvalds
>>>
>>> This came from the gcc build?
>>
>> yes, very early in the build process, IIRC this line was repeated a
>> few times and the build just stalled.
>
> Ok, we're bringing out the crazy hacks now.
>
> The attached patch is just insane, doesn't really even work in
> general, and only even compiles on 64-bit. But it should work in
> *practice* to find if somebody adds the same RCU head to the RCU lists
> twice, and ignore the second time it happens (and give a warning that
> hopefully pinpoints the backtrace).
>
> It's ugly. It's broken. It may not work. In other words, I'm not proud
> of it. But you seem to be the only one able to trigger the issue
> easily, willing to try crazy crap, so "tag, you're it". Maybe this
> gives us more information. And maybe it doesn't, and I'm totally wrong
> about the whole "rcu head added twice" theory.

That's all I could get so far:
https://gist.github.com/anonymous/5279255

Losing wireless is generally the start signal of controlled demolition
of the machine.
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