From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1761182Ab0FRM6v (ORCPT ); Fri, 18 Jun 2010 08:58:51 -0400 Received: from moutng.kundenserver.de ([212.227.17.10]:63729 "EHLO moutng.kundenserver.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758549Ab0FRM6u (ORCPT ); Fri, 18 Jun 2010 08:58:50 -0400 From: Arnd Bergmann To: Frederic Weisbecker Subject: [PATCH] tty: avoid recursive BTM in pty_close Date: Fri, 18 Jun 2010 14:58:07 +0200 User-Agent: KMail/1.12.2 (Linux/2.6.31-19-generic; KDE/4.3.2; x86_64; ; ) Cc: Tony Luck , Alan Cox , linux-kernel@vger.kernel.org, Greg KH , Thomas Gleixner , Andrew Morton , John Kacur , Al Viro , Ingo Molnar References: <1273957196-13768-1-git-send-email-arnd@arndb.de> <201006172348.08180.arnd@arndb.de> <20100617220926.GC5345@nowhere> In-Reply-To: <20100617220926.GC5345@nowhere> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201006181458.07687.arnd@arndb.de> X-Provags-ID: V01U2FsdGVkX18WqYs2qirS5Y2L9gTpO90TZV6BIGIALdcs7DG CixBI3LJuvy1bDSYPA7jkRZ4WTSOK/RXdZqhXJs3IaZwavh2p6 J3qp/C1QD1jqrf+Z782cw== Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When the console has been redirected, a hangup of the tty will cause tty_release to be called under the big tty_mutex, which leads to a deadlock because hangup is also called under the BTM. This moves the BTM deeper into the tty_hangup function so we can close the redirected tty without holding the BTM. In case of pty, we now need to drop the BTM before calling tty_vhangup. Signed-off-by: Arnd Bergmann --- drivers/char/pty.c | 4 +++- drivers/char/tty_io.c | 24 ++++++++++++------------ 2 files changed, 15 insertions(+), 13 deletions(-) --- On Friday 18 June 2010, Frederic Weisbecker wrote: > > - tty_vhangup_locked(tty->link); > > + unlock_kernel(); > > + tty_vhangup(tty->link); > > + lock_kernel(); > > > > Don't you mean tty_unlock / tty_lock there? Yes, thanks for catching this. I did test this patch yesterday night (it was late) with CONFIG_TTY_MUTEX disabled, as in Tony's configuration, but I did not realize that I broke the other configuration in turn. I'd like to get Alan's opinion on whether he considers the change in pty.c safe. diff --git a/drivers/char/pty.c b/drivers/char/pty.c index c9af9ff..acff19f 100644 --- a/drivers/char/pty.c +++ b/drivers/char/pty.c @@ -62,7 +62,9 @@ static void pty_close(struct tty_struct *tty, struct file *filp) if (tty->driver == ptm_driver) devpts_pty_kill(tty->link); #endif - tty_vhangup_locked(tty->link); + tty_unlock(); + tty_vhangup(tty->link); + tty_lock(); } } diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c index 5db354d..6bf6d36 100644 --- a/drivers/char/tty_io.c +++ b/drivers/char/tty_io.c @@ -471,7 +471,7 @@ void tty_wakeup(struct tty_struct *tty) EXPORT_SYMBOL_GPL(tty_wakeup); /** - * do_tty_hangup - actual handler for hangup events + * __tty_hangup - actual handler for hangup events * @work: tty device * * This can be called by the "eventd" kernel thread. That is process @@ -492,7 +492,7 @@ EXPORT_SYMBOL_GPL(tty_wakeup); * tasklist_lock to walk task list for hangup event * ->siglock to protect ->signal/->sighand */ -void tty_vhangup_locked(struct tty_struct *tty) +void __tty_hangup(struct tty_struct *tty) { struct file *cons_filp = NULL; struct file *filp, *f = NULL; @@ -512,10 +512,12 @@ void tty_vhangup_locked(struct tty_struct *tty) } spin_unlock(&redirect_lock); + tty_lock(); + /* inuse_filps is protected by the single tty lock, this really needs to change if we want to flush the workqueue with the lock held */ - check_tty_count(tty, "do_tty_hangup"); + check_tty_count(tty, "tty_hangup"); file_list_lock(); /* This breaks for file handles being sent over AF_UNIX sockets ? */ @@ -594,6 +596,9 @@ void tty_vhangup_locked(struct tty_struct *tty) */ set_bit(TTY_HUPPED, &tty->flags); tty_ldisc_enable(tty); + + tty_unlock(); + if (f) fput(f); } @@ -603,9 +608,7 @@ static void do_tty_hangup(struct work_struct *work) struct tty_struct *tty = container_of(work, struct tty_struct, hangup_work); - tty_lock(); - tty_vhangup_locked(tty); - tty_unlock(); + __tty_hangup(tty); } /** @@ -643,13 +646,12 @@ void tty_vhangup(struct tty_struct *tty) printk(KERN_DEBUG "%s vhangup...\n", tty_name(tty, buf)); #endif - tty_lock(); - tty_vhangup_locked(tty); - tty_unlock(); + __tty_hangup(tty); } EXPORT_SYMBOL(tty_vhangup); + /** * tty_vhangup_self - process vhangup for own ctty * @@ -727,10 +729,8 @@ void disassociate_ctty(int on_exit) if (tty) { tty_pgrp = get_pid(tty->pgrp); if (on_exit) { - tty_lock(); if (tty->driver->type != TTY_DRIVER_TYPE_PTY) - tty_vhangup_locked(tty); - tty_unlock(); + tty_vhangup(tty); } tty_kref_put(tty); } else if (on_exit) { -- 1.7.0.4