linux-kernel - Re: [PATCH 01/20 -v5] printk - dont wakeup klogd with interrupts disabled

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Message-ID: <20080124103550.GA3433@elf.ucw.cz>
Date:	Thu, 24 Jan 2008 11:35:50 +0100
From:	Pavel Machek <pavel@....cz>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	Daniel Walker <dwalker@...sta.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	LKML <linux-kernel@...r.kernel.org>, Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Christoph Hellwig <hch@...radead.org>,
	Gregory Haskins <ghaskins@...ell.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Tim Bird <tim.bird@...sony.com>,
	Sam Ravnborg <sam@...nborg.org>,
	"Frank Ch. Eigler" <fche@...hat.com>,
	Jan Kiszka <jan.kiszka@...mens.com>,
	John Stultz <johnstul@...ibm.com>,
	Arjan van de Ven <arjan@...radead.org>,
	Steven Rostedt <srostedt@...hat.com>
Subject: Re: [PATCH 01/20 -v5] printk - dont wakeup klogd with interrupts
	disabled

On Wed 2008-01-23 12:25:09, Mathieu Desnoyers wrote:
> * Daniel Walker (dwalker@...sta.com) wrote:
> > 
> > On Wed, 2008-01-23 at 11:02 -0500, Steven Rostedt wrote:
> > 
> > > +	if (!irqs_disabled() && wake_klogd)
> > >  		wake_up_klogd();
> > 
> > This causes a regression .. When printk is called during an OOPS in
> > kernels without this change then the OOPS will get logged, since the
> > logging process (klogd) is woken to handle the messages.. If you apply
> > this change klogd doesn't wakeup, and hence doesn't log the oops.. So if
> > you remove the wakeup here you have to add it someplace else to maintain
> > the logging ..
> > 
> > (I'm not theorizing here, I have defects logged against this specific
> > piece of code..)
> > 
> 
> Can we change this for :
> if (!(irqs_disabled() && !oops_in_progress) && wake_klogd)
>   wake_up_klogd();
> 
> ?

That's wrong, too.

Just make wake_up_klogd do trylock, if it finds that it can't get
neccessary locks, printk(KERN_ALERT) so at least console gets the
message, but proceed without the lock.
								Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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