Date: Thu, 19 Oct 2017 12:44:29 +1100 From: "Tobin C. Harding" <me@...in.cc> To: "Jason A. Donenfeld" <Jason@...c4.com> Cc: Sergey Senozhatsky <sergey.senozhatsky.work@...il.com>, 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 03:36:20AM +0200, Jason A. Donenfeld wrote: > 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. Cool! That's the solution I've been looking for since day 1. You the man. thanks, Tobin.
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