linux-kernel - Re: [debug patch] printk: Add a printk killswitch to robustify NMI watchdog messages

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]

Date:	Mon, 06 Jun 2011 17:09:49 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Ingo Molnar <mingo@...e.hu>
Cc:	Arne Jansen <lists@...-jansens.de>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	mingo@...hat.com, hpa@...or.com, linux-kernel@...r.kernel.org,
	efault@....de, npiggin@...nel.dk, akpm@...ux-foundation.org,
	frank.rowand@...sony.com, tglx@...utronix.de,
	linux-tip-commits@...r.kernel.org
Subject: Re: [debug patch] printk: Add a printk killswitch to robustify NMI
 watchdog messages

On Mon, 2011-06-06 at 16:58 +0200, Ingo Molnar wrote:
> * Peter Zijlstra <peterz@...radead.org> wrote:
> 
> > On Sun, 2011-06-05 at 17:13 +0200, Ingo Molnar wrote:
> > 
> > > Now, this patch alone just removes a debugging check - but i'm not 
> > > sure the debugging check is correct - we take the pi_lock in a raw 
> > > way - which means it's not lockdep covered.
> > 
> > Ever since tglx did s/raw_/arch_/g raw_ is covered by lockdep.
> 
> It's not lockdep covered due to the lockdep_off(), or am i missing 
> something?

Your initial stmt was about the raw_ part, raw_ locks are tracked by
lockdep ever since tglx renamed them to arch_ and introduced new raw_
primitives.

But yeah, the lockdep_off() stuff also disables all tracking, on top of
that it also makes lock_is_held() return an unconditional false (even if
the lock was acquired before lockdep_off and thus registered).

My patch that fixes lock_is_held() should avoid false
lockdep_assert_held() explosions and this this printk() while rq->lock
problem.

Removing lockdep_off() usage from printk() would also be nice, but Mike
triggered logbuf_lock <-> rq->lock inversion with that due to the
up(&console_sem) wakeup muck.

Ideally we'd pull the up() out from under logbuf_lock, am looking at
that.
--
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/