linux-kernel - Re: [PATCH 1/3] printk: Release console_sem after logbuf

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Message-Id: <20110609140714.fc9ea187.akpm@linux-foundation.org>
Date:	Thu, 9 Jun 2011 14:07:14 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	Ingo Molnar <mingo@...e.hu>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	linux-kernel@...r.kernel.org, efault@....de,
	Arne Jansen <lists@...-jansens.de>
Subject: Re: [PATCH 1/3] printk: Release console_sem after logbuf_lock

On Thu, 09 Jun 2011 22:54:43 +0200
Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:

> On Thu, 2011-06-09 at 22:27 +0200, Ingo Molnar wrote:
> 
> > > > @@ -1271,8 +1273,8 @@ void console_unlock(void)
> > > >  	if (unlikely(exclusive_console))
> > > >  		exclusive_console = NULL;
> > > >  
> > > > -	up(&console_sem);
> > > >  	spin_unlock_irqrestore(&logbuf_lock, flags);
> > > > +	up(&console_sem);
> > > >  	if (wake_klogd)
> > > >  		wake_up_klogd();
> > > >  }
> > > 
> > > I have a horrible feeling that I put the up() inside logbuf_lock for
> > > Special And Cunning Reasons.  But I'm struggling to work out what they
> > > might have been and my archives only go back to October 2000(!).
> > > 
> > > Hate it when that happens.
> > 
> > Heh, here's what i told Peter two days ago when i saw that chunk:
> > 
> >   => Subject: printk: Release console_sem after logbuf_lock
> >   => i have some vague memories about some sort of complication in that area ...
> >   => but don't remember the specifics
> >   => only a 'there be dragons' mental marker
> 
> Right, my reply was that I couldn't convince myself unlock order could
> make a difference, but clearly I can easily have missed something
> subtle.

I wish I could find the darned patch.  I have a file here
no-console-lock-2.patch which was last diffed on October 7, 1999 but it
has no changelog :(

But this:
http://lkml.indiana.edu/hypermail/linux/kernel/0109.2/0127.html is Sep
2001 and I have an earlier (unchangelogged) no-console-lock.patch diffed
against 2.4.2 in March 2001.

It's odd that the patch (and changelog) don't appear in my lkml
archives.  Sigh, http://www.youtube.com/watch?v=oO3YmT2d-8k


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