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Date: Thu, 19 Oct 2017 03:36:20 +0200
From: "Jason A. Donenfeld" <Jason@...c4.com>
To: Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>
Cc: "Tobin C. Harding" <me@...in.cc>, kernel-hardening@...ts.openwall.com, 
	"Theodore Ts'o" <tytso@....edu>, Linus Torvalds <torvalds@...ux-foundation.org>, 
	Kees Cook <keescook@...omium.org>, Paolo Bonzini <pbonzini@...hat.com>, 
	Tycho Andersen <tycho@...ker.com>, "Roberts, William C" <william.c.roberts@...el.com>, 
	Tejun Heo <tj@...nel.org>, Jordan Glover <Golden_Miller83@...tonmail.ch>, 
	Greg KH <gregkh@...uxfoundation.org>, Petr Mladek <pmladek@...e.com>, 
	Joe Perches <joe@...ches.com>, Ian Campbell <ijc@...lion.org.uk>, 
	Sergey Senozhatsky <sergey.senozhatsky@...il.com>, Catalin Marinas <catalin.marinas@....com>, 
	Will Deacon <wilal.deacon@....com>, Steven Rostedt <rostedt@...dmis.org>, 
	Chris Fries <cfries@...gle.com>, Dave Weinstein <olorin@...gle.com>, 
	Daniel Micay <danielmicay@...il.com>, Djalal Harouni <tixxdz@...il.com>, 
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5] printk: hash addresses printed with %p

On Thu, Oct 19, 2017 at 3:31 AM, Sergey Senozhatsky
<sergey.senozhatsky.work@...il.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.

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