From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933867Ab1KJDVS (ORCPT ); Wed, 9 Nov 2011 22:21:18 -0500 Received: from cantor2.suse.de ([195.135.220.15]:41692 "EHLO mx2.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S933816Ab1KJDVN (ORCPT ); Wed, 9 Nov 2011 22:21:13 -0500 X-Mailbox-Line: From gregkh@clark.kroah.org Wed Nov 9 13:27:01 2011 Message-Id: <20111109212701.205218062@clark.kroah.org> User-Agent: quilt/0.48-16.4 Date: Wed, 09 Nov 2011 13:25:31 -0800 From: Greg KH To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: torvalds@linux-foundation.org, akpm@linux-foundation.org, alan@lxorguk.ukuu.org.uk, Kautuk Consul Subject: [009/262] staging: quatech_usb2: Potential lost wakeup scenario in TIOCMIWAIT In-Reply-To: <20111109212847.GA20838@kroah.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.0-stable review patch. If anyone has any objections, please let me know. ------------------ From: Kautuk Consul commit e8df1674d383d2ecc6efa8d7dba74c03aafdfdd7 upstream. If the usermode app does an ioctl over this serial device by using TIOCMIWAIT, then the code will wait by setting the current task state to TASK_INTERRUPTIBLE and then calling schedule(). This will be woken up by the qt2_process_modem_status on URB completion when the port_extra->shadowMSR is set to the new modem status. However, this could result in a lost wakeup scenario due to a race in the logic in the qt2_ioctl(TIOCMIWAIT) loop and the URB completion for new modem status in qt2_process_modem_status. Due to this, the usermode app's task will continue to sleep despite a change in the modem status. Signed-off-by: Kautuk Consul Signed-off-by: Greg Kroah-Hartman --- drivers/staging/quatech_usb2/quatech_usb2.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) --- a/drivers/staging/quatech_usb2/quatech_usb2.c +++ b/drivers/staging/quatech_usb2/quatech_usb2.c @@ -916,9 +916,10 @@ static int qt2_ioctl(struct tty_struct * dbg("%s() port %d, cmd == TIOCMIWAIT enter", __func__, port->number); prev_msr_value = port_extra->shadowMSR & QT2_SERIAL_MSR_MASK; + barrier(); + __set_current_state(TASK_INTERRUPTIBLE); while (1) { add_wait_queue(&port_extra->wait, &wait); - set_current_state(TASK_INTERRUPTIBLE); schedule(); dbg("%s(): port %d, cmd == TIOCMIWAIT here\n", __func__, port->number); @@ -926,9 +927,12 @@ static int qt2_ioctl(struct tty_struct * /* see if a signal woke us up */ if (signal_pending(current)) return -ERESTARTSYS; + set_current_state(TASK_INTERRUPTIBLE); msr_value = port_extra->shadowMSR & QT2_SERIAL_MSR_MASK; - if (msr_value == prev_msr_value) + if (msr_value == prev_msr_value) { + __set_current_state(TASK_RUNNING); return -EIO; /* no change - error */ + } if ((arg & TIOCM_RNG && ((prev_msr_value & QT2_SERIAL_MSR_RI) == (msr_value & QT2_SERIAL_MSR_RI))) || @@ -941,6 +945,7 @@ static int qt2_ioctl(struct tty_struct * (arg & TIOCM_CTS && ((prev_msr_value & QT2_SERIAL_MSR_CTS) == (msr_value & QT2_SERIAL_MSR_CTS)))) { + __set_current_state(TASK_RUNNING); return 0; } } /* end inifinite while */