linux-kernel - Re: [RFC 7/9] ppp: use big tty mutex

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Message-Id: <201003310939.15324.arnd@arndb.de>
Date:	Wed, 31 Mar 2010 09:39:14 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Américo Wang <xiyou.wangcong@...il.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>, Greg KH <gregkh@...e.de>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andrew Morton <akpm@...ux-foundation.org>,
	John Kacur <jkacur@...hat.com>,
	Al Viro <viro@...iv.linux.org.uk>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [RFC 7/9] ppp: use big tty mutex

On Wednesday 31 March 2010 06:37:12 Américo Wang wrote:
> > @@ -362,7 +362,8 @@ static const int npindex_to_ethertype[NUM_NP] = {
> >  */
> >  static int ppp_open(struct inode *inode, struct file *file)
> >  {
> > -       cycle_kernel_lock();
> > +       tty_lock();
> > +       tty_unlock();
> 
> I don't really get your point here. :) Why do you do this?

This is a blind conversion of the API from the common BKL functions to
the TTY lock functions. There is no cycle_tty_lock(), so I'm manually
doing the cycle.

The reason why cycle_kernel_lock() was introduced in the first place
is that some drivers may depend on the open() function not returning
while another CPU holds the BKL. I did not feel qualified (or motivated)
to determine if the ppp code has the behavior, so I left it at this.

	Arnd
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