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: <1271693928.1676.18.camel@laptop>
Date:	Mon, 19 Apr 2010 18:18:48 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Andrea Arcangeli <aarcange@...hat.com>
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, 2010-04-19 at 18:11 +0200, Andrea Arcangeli wrote:
> On Mon, Apr 19, 2010 at 05:45:05PM +0200, Peter Zijlstra wrote:
> > Wouldn't a longer poison be more recognisable? Also, shouldn't this use
> > POISON_POINTER_DELTA?
> > 
> > Something like:
> > 
> > #define HUGETBL_POISON	((void *) 0x00300300 + POISON_POINTER_DELTA)
> > 
> > 0x2e5 isn't that high, I've had actual derefs in that range.
> 
> The default at kernel config time sets only 4k as unmapped (I think
> it's a very bad default for 64bit archs), so above 4k userland can map
> it and you can have actual derefs with 0x00300300 but not with Mel's
> preferred <0x1000 address. So the address must be <0x1000.

Well, most poison values have that problem and still we have them. Also
on 64bit machines you can use POISON_POINTER_DELTA to map it outside the
virtual address range.


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