linux-kernel - Re: [PATCH] TTY: Fix loss of echoed characters (2nd follow-on PATCH attached)

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Date:	Tue, 9 Sep 2008 10:43:25 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Joe Peterson <joe@...rush.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] TTY: Fix loss of echoed characters (2nd follow-on PATCH
 attached)

On Tue, 9 Sep 2008 11:55:36 +0100 Alan Cox <alan@...rguk.ukuu.org.uk> wrote:

> On Mon, 8 Sep 2008 17:32:50 -0700
> Andrew Morton <akpm@...ux-foundation.org> wrote:
> 
> > On Mon, 08 Sep 2008 10:11:46 -0600
> > Joe Peterson <joe@...rush.com> wrote:
> > 
> > > +	spin_lock_irqsave(&tty->echo_lock, flags);
> > >  	lock_kernel();
> > 
> > Taking a spinlock outside lock_kernel() isn't good, and is quite unusual.
> > 
> > - It might be ab/ba deadlockable (I didn't check) (I trust you always
> >   test with lockdep enabled?)
> 
> lock_kernel can sleep.

That used to be the case, but the mutex_lock() version of the bkl got
removed.  It may of course come back.

> Its not allowed...
> 

yup.
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