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

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Message-ID: <CA+55aFz-0J3uhJC-00AJ0R-4TVOYqFGJk0h5x0HmaX+JR6_MYQ@mail.gmail.com>
Date:	Tue, 2 Apr 2013 10:52:15 -0700
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Sasha Levin <sasha.levin@...cle.com>
Cc:	Peter Hurley <peter@...leysoftware.com>,
	Dave Jones <davej@...hat.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Rik van Riel <riel@...riel.com>,
	Davidlohr Bueso <davidlohr.bueso@...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>,
	Stanislav Kinsbursky <skinsbursky@...allels.com>
Subject: Re: ipc,sem: sysv semaphore scalability

On Tue, Apr 2, 2013 at 9:08 AM, Sasha Levin <sasha.levin@...cle.com> wrote:
>
> By just playing with the 'msgsz' parameter with MSG_COPY set.

Hmm. Looking closer, I suspect you're testing without commit
88b9e456b164 ("ipc: don't allocate a copy larger than max"). That
should limit the size passed in to prepare_copy -> load_copy to
msg_ctlmax.

Now, I think it's possibly still a good idea to limit bufsz to INT_MAX
regardless, but as far as I can see that prepare_copy -> load_copy
path is the only place that can get confused. Everybody else uses
size_t (or "long" in the case of r_maxsize) as far as I can tell.

        Linus
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