linux-kernel - Re: [PATCH 1/1] Fix: trace sched switch start/stop racy updates

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <20190820135612.GS2332@hirez.programming.kicks-ass.net>
Date:   Tue, 20 Aug 2019 15:56:12 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Joel Fernandes <joel@...lfernandes.org>,
        Alan Stern <stern@...land.harvard.edu>,
        rostedt <rostedt@...dmis.org>,
        Valentin Schneider <valentin.schneider@....com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        paulmck <paulmck@...ux.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Will Deacon <will.deacon@....com>,
        David Howells <dhowells@...hat.com>
Subject: Re: [PATCH 1/1] Fix: trace sched switch start/stop racy updates

On Sat, Aug 17, 2019 at 01:08:02AM -0700, Linus Torvalds wrote:

> The data tearing issue is almost a non-issue. We're not going to add
> WRITE_ONCE() to these kinds of places for no good reason.

Paulmck actually has an example of that somewhere; ISTR that particular
case actually got fixed by GCC, but I'd really _love_ for some compiler
people (both GCC and LLVM) to state that their respective compilers will
not do load/store tearing for machine word sized load/stores.

Without this written guarantee (which supposedly was in older GCC
manuals but has since gone missing), I'm loathe to rely on it.

Yes, it is very rare, but it is a massive royal pain to debug if/when it
does do happen.