Re: [2.6.33-rc5] starting emacs makes lockdep warning

From: Al Viro
Date: Tue Jan 26 2010 - 01:54:47 EST

On Tue, Jan 26, 2010 at 02:24:30PM +0800, Am??rico Wang wrote:
> On Tue, Jan 26, 2010 at 2:07 PM, Al Viro <viro@xxxxxxxxxxxxxxxxxx> wrote:
> > On Tue, Jan 26, 2010 at 02:01:12PM +0800, Am??rico Wang wrote:
> >
> >> I agree, it seems that patch is useless, since we already
> >> do lock_kernel() before calling __f_setown()...
> >
> > What's to prevent pid from being freed under us? ??BKL won't...
> >
> Hmm, I don't fully understand the race here. If it is used to protect
> 'pid' which we get from 'tty->pgrp' or 'current', in the former case,
> it is protected by 'tty->ctrl_lock', in the later case, it doesn't need
Without that patch it isn't.

> the lock. So it's not necessary to protect 'pid' by 'tty->crtl_lock'.
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