[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <1307652883.2497.1028.camel@laptop>
Date: Thu, 09 Jun 2011 22:54:43 +0200
From: Peter Zijlstra <a.p.zijlstra@...llo.nl>
To: Ingo Molnar <mingo@...e.hu>
Cc: Andrew Morton <akpm@...ux-foundation.org>,
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, 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.
> and i have to say that when i found a boot lockup during testing i
> was not surprised very much :)
But you found a lockup on the second patch, not this one.
Also, this patch is important for #3, where we want to take logbuf_lock
under the semaphore internal lock, that too would preclude us doing that
up() in the old location.
--
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/
Powered by blists - more mailing lists