Follow @Openwall on Twitter for new release announcements and other news
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Date: Mon, 24 Apr 2017 13:33:11 -0700
From: Kees Cook <>
To: PaX Team <>
Cc: Peter Zijlstra <>, LKML <>, 
	Eric Biggers <>, Christoph Hellwig <>, 
	"" <>, James Bottomley <>, 
	Elena Reshetova <>, Hans Liljestrand <>, 
	David Windsor <>, "" <>, Ingo Molnar <>, 
	Arnd Bergmann <>, Greg Kroah-Hartman <>, Jann Horn <>, 
	"David S. Miller" <>, linux-arch <>, 
	"" <>
Subject: Re: [PATCH] x86/refcount: Implement fast refcount_t handling

On Mon, Apr 24, 2017 at 4:00 AM, PaX Team <> wrote:
> On 24 Apr 2017 at 10:32, Peter Zijlstra wrote:
>> On Fri, Apr 21, 2017 at 03:09:39PM -0700, Kees Cook wrote:
>> > This patch ports the x86-specific atomic overflow handling from PaX's
>> > PAX_REFCOUNT to the upstream refcount_t API. This is an updated version
>> > from PaX that eliminates the saturation race condition by resetting the
>> > atomic counter back to the INT_MAX saturation value on both overflow and
>> > underflow. To win a race, a system would have to have INT_MAX threads
>> > simultaneously overflow before the saturation handler runs.
> note that the above is wrong (and even contradicting itself and the code).

True, this changelog could be more accurate (it resets to INT_MAX on
overflow and INT_MIN on underflow). I think I'm right in saying that a
system would need INT_MAX threads running a refcount_inc() (and a
refcount_dec_and_test() at exactly the right moment) before the reset
handler got scheduled, though, yes?

I'll attempt to clarify this.


Kees Cook
Pixel Security

Powered by blists - more mailing lists

Confused about mailing lists and their use? Read about mailing lists on Wikipedia and check out these guidelines on proper formatting of your messages.