linux-kernel - Re: IRQ off latency of printk is very high

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:	Thu, 1 Nov 2007 22:11:53 +0100
From:	Pavel Machek <pavel@....cz>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	Tim Bird <tim.bird@...sony.com>, Matt Mackall <mpm@...enic.com>,
	linux kernel <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>, Jon Smirl <jonsmirl@...oo.com>
Subject: Re: IRQ off latency of printk is very high

Hi!

> > > It seems draconian to drain the entire buffer with ints disabled.
> > > Is it possible to break this up and send out smaller chunks
> > > at a time?  Maybe by putting a chunk loop in release_console_sem()?
> > 
> > Well, I believe someone got
> > 
> > DDetetccctted ed 113223 HHzz CPUCPU
> > 
> > in his dmesg, and now we have this 'draconian' locking. How can we
> > prevent mangled messages without it?
> 
> The main interest seems to be to protect from mixed printk output
> between different CPUs in process context. I don't think it would be
> that bad if interrupts come and output error messages in the middle of a
> printk, isn't it ?
> 
> therefore, could we do something like :
> 
> 
> if (!in_irq())
>   spin_lock(&logbuf_lock);
> ...
> if (!in_irq())
>   spin_unlock(&logbuf_lock);
> 
> ? (yes, this is a crazy idea)

Two messages in atomic sections on different cpus could still be mixed
:-). But yes, something like this may be the way to go.
									Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
-
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/