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From: Arnd Bergmann <arnd@arndb.de>
To: =?utf-8?q?Am=C3=A9rico_Wang?= <xiyou.wangcong@gmail.com>
Subject: Re: [RFC 7/9] ppp: use big tty mutex
Date: Wed, 31 Mar 2010 09:39:14 +0200
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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