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Date: Thu, 19 Oct 2017 12:44:29 +1100
From: "Tobin C. Harding" <me@tobin.cc>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: Sergey Senozhatsky <sergey.senozhatsky.work@gmail.com>,
        kernel-hardening@lists.openwall.com, "Theodore Ts'o" <tytso@mit.edu>,
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        Sergey Senozhatsky <sergey.senozhatsky@gmail.com>,
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Subject: Re: [PATCH v5] printk: hash addresses printed with %p
Message-ID: <20171019014429.GG31318@eros>
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On Thu, Oct 19, 2017 at 03:36:20AM +0200, Jason A. Donenfeld wrote:
> On Thu, Oct 19, 2017 at 3:31 AM, Sergey Senozhatsky
> <sergey.senozhatsky.work@gmail.com> wrote:
> > On (10/19/17 03:03), Jason A. Donenfeld wrote:
> > [..]
> >> 1) Go back to the spinlock yourself.
> >
> > so we ruled out NMI deadlocks?
> 
> Oh, right. No, I haven't thought through this enough to rule it out.
> Indeed if that's an issue, the locks in the _once code will also be an
> issue.
> 
> So if locking is totally impossible, then a race-free way of doing
> this is with a tri-state compare and exchange. Things are either: in
> state 1: no key, state 2: getting key, state 3: have key. If state 1
> or 2, print the placeholder token. If state 3, do the hashing.

Cool! That's the solution I've been looking for since day 1. You the man.

thanks,
Tobin.