linux-kernel - Re: [PATCH] Fix race/oops in tty layer after BKL pushdown

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Message-ID: <20080811085920.59b278b9@lxorguk.ukuu.org.uk>
Date:	Mon, 11 Aug 2008 08:59:20 +0100
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Christian Borntraeger <borntraeger@...ibm.com>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Olaf Schnapper <os@...ibm.com>
Subject: Re: [PATCH] Fix race/oops in tty layer after BKL pushdown

> Please review and consider to apply:
> 
> Signed-off-by: Christian Borntraeger <borntraeger@...ibm.com>
> ---
>  drivers/char/tty_io.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> Index: kvm/drivers/char/tty_io.c
> ===================================================================
> --- kvm.orig/drivers/char/tty_io.c
> +++ kvm/drivers/char/tty_io.c
> @@ -1161,8 +1161,8 @@ void disassociate_ctty(int on_exit)
>  	tty = get_current_tty();
>  	if (tty) {
>  		tty_pgrp = get_pid(tty->pgrp);
> -		mutex_unlock(&tty_mutex);
>  		lock_kernel();
> +		mutex_unlock(&tty_mutex);
>  		/* XXX: here we race, there is nothing protecting tty */
>  		if (on_exit && tty->driver->type != TTY_DRIVER_TYPE_PTY)
>  			tty_vhangup(tty);

For upstream (see -next tree) I have pushed a refcounting solution (or at
least I hope its a solution) to the ttydev tree. For 2.6.26 your approach
partially fixes this and certainly doesn't make it worse so I'll now push
it onwards.

Alan
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