From d6bf984a19fba5bf1d8efc86f2b1dc7c3e71b614 Mon Sep 17 00:00:00 2001 From: Kautuk Consul Date: Wed, 14 Sep 2011 08:56:21 +0530 Subject: [PATCH] staging: quatech_usb2: Potential lost wakeup scenario in TIOCMIWAIT 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 Signed-off-by: Paul Gortmaker --- drivers/staging/quatech_usb2/quatech_usb2.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/drivers/staging/quatech_usb2/quatech_usb2.c b/drivers/staging/quatech_usb2/quatech_usb2.c index 1561f74a413b..3ca3c2adcc1a 100644 --- a/drivers/staging/quatech_usb2/quatech_usb2.c +++ b/drivers/staging/quatech_usb2/quatech_usb2.c @@ -921,9 +921,10 @@ static int qt2_ioctl(struct tty_struct *tty, struct file *file, 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); @@ -931,9 +932,12 @@ static int qt2_ioctl(struct tty_struct *tty, struct file *file, /* 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))) || @@ -946,6 +950,7 @@ static int qt2_ioctl(struct tty_struct *tty, struct file *file, (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 */ -- 2.39.5