linux-kernel - Re: [PATCH 1/1] TTY: don't allow reopen when ldisc is changing

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Date:	Sat, 27 Nov 2010 09:50:38 +0100
From:	Jiri Slaby <jslaby@...e.cz>
To:	Kyle McMartin <kyle@...artin.ca>
CC:	gregkh@...e.de, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, Alan Cox <alan@...rguk.ukuu.org.uk>
Subject: Re: [PATCH 1/1] TTY: don't allow reopen when ldisc is changing

On 11/27/2010 03:59 AM, Kyle McMartin wrote:
> I'm poking around to see, I think maybe something might be dropping
> locks in the callchain that gives us a window where this might be
> possible...

Of course, that's the case:
        clear_bit(TTY_LDISC, &tty->flags);
        tty_unlock();
        cancel_delayed_work_sync(&tty->buf.work);
        mutex_unlock(&tty->ldisc_mutex);

        tty_lock();
        mutex_lock(&tty->ldisc_mutex);

in tty_ldisc_hangup. Hence my point 1) from previous posts doesn't hold too:
1) __tty_hangup from tty_ldisc_hangup to tty_ldisc_enable. During this
section tty_lock is held.

I will check, how to fix this.

thanks,
-- 
js
suse labs
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