linux-kernel - Re: [PATCH] [RFC] Potential fix for leapsecond caused futex related load spikes

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] [day] [month] [year] [list]

Message-ID: <4FF03BDC.9070208@computer.org>
Date:	Sun, 01 Jul 2012 14:00:28 +0200
From:	Jan Ceuleers <jan.ceuleers@...puter.org>
To:	John Stultz <johnstul@...ibm.com>
CC:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	stable@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] [RFC] Potential fix for leapsecond caused futex related
 load spikes

On 07/01/2012 11:36 AM, John Stultz wrote:
> I believe this issue is due to the leapsecond being added without
> calling clock_was_set() to notify the hrtimer subsystem of the
> change. (Although I've not yet chased all the way down to the
> hrtimer code to validate exactly what's going on there).

For the benefit of -stable:

Am I right in thinking that, if the analysis is confirmed, this was
caused by the following commit:

commit 746976a301ac9c9aa10d7d42454f8d6cdad8ff2b
Author: Thomas Gleixner <tglx@...utronix.de>
Date:   Tue Jul 3 20:05:20 2007 +0200

NTP: remove clock_was_set() call to prevent deadlock

The clock_was_set() call in seconds_overflow() which happens only when
leap seconds are inserted / deleted is wrong in two aspects:

1. it results in a call to on_each_cpu() with interrupts disabled
2. it is potential deadlock source vs. call_lock in smp_call_function()

The only possible side effect of the removal might be, that an absolute
CLOCK_REALTIME timer fires 1 second too late, in the rare case of leap
second deletion and an absolute CLOCK_REALTIME timer which expires in
the affected time frame. It will never fire too early.

This was probably observed by the reporter of a June 30th -> July 1st
hang: http://lkml.org/lkml/2007/7/3/103

A similar problem was observed by Dave Jones, who provided a screen shot
with a lockdep back trace, which allowed to analyse the problem.

Sob: Thomas Gleixner <tglx@...utronix.de>
Ab: Ingo Molnar <mingo@...e.hu>
Sob: Linus Torvalds <torvalds@...ux-foundation.org>
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/