linux-kernel - Re: process 'stuck' at exit.

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Message-ID: <CA+55aFxLbFWhgzg=Rn0rhUpoOjbTE3QqUSxHTsCyk8GjDUFxJg@mail.gmail.com>
Date:	Tue, 10 Dec 2013 14:19:43 -0800
From:	Linus Torvalds <torvalds@...ux-foundation.org>
To:	Dave Jones <davej@...hat.com>, Oleg Nesterov <oleg@...hat.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Darren Hart <dvhart@...ux.intel.com>,
	Andrea Arcangeli <aarcange@...hat.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Mel Gorman <mgorman@...e.de>
Subject: Re: process 'stuck' at exit.

On Tue, Dec 10, 2013 at 1:57 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
>
> So it looks like __get_user_pages_fast() fails, and keeps failing.

Hmm.. Is any of the addresses unchecked, perhaps?
__get_user_pages_fast() does an access_ok() check, while
get_user_pages_fast() does *not* seem to do one.

That looks a bit dangerous. Yeah, users should have checked the
address range, but there really is no reason not to do it in
get_user_pages_fast().

And it looks like the futex code is actually seriously buggered. It
only does the access_ok() check for the non-shared case.

Why?

Shouldn't we do something like the attached?

               Linus

View attachment "patch.diff" of type "text/plain" (1379 bytes)