linux-kernel - Re: Process-shared futexes on hugepages puts the kernel in an infinite loop in 2.6.32.11; is this fixed now?

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Message-ID: <20100419163217.GB32034@random.random>
Date:	Mon, 19 Apr 2010 18:32:17 +0200
From:	Andrea Arcangeli <aarcange@...hat.com>
To:	Peter Zijlstra <peterz@...radead.org>
Cc:	Mel Gorman <mel@....ul.ie>, r6144 <rainy6144@...il.com>,
	linux-kernel@...r.kernel.org, Darren Hart <dvhltc@...ibm.com>,
	tglx <tglx@...utronix.de>,
	Lee Schermerhorn <lee.schermerhorn@...com>
Subject: Re: Process-shared futexes on hugepages puts the kernel in an
 infinite loop in 2.6.32.11; is this fixed now?

On Mon, Apr 19, 2010 at 06:18:48PM +0200, Peter Zijlstra wrote:
> Well, most poison values have that problem and still we have them. Also

That would better be fixed too to stay <4096 for higher chance of
bug-detection, it doesn't make this case correct ;).

> on 64bit machines you can use POISON_POINTER_DELTA to map it outside the
> virtual address range.

We've thousands of magic values there, I don't see much benefit from
POISON_POINTER_DELTA other than being able to call it
0xdeadbeef+POISON_POINTER_DELTA ;). We always look the assembly to
find the actual real raw pointer value (without the field offset) so I
think using a range between 0xaaa and 0xbbb for the error pointers, is
functional enough, but it's up to you as long as it is a address range
that can't be used by userland it's surely ok ;).
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