]> git.openfabrics.org - ~shefty/rdma-dev.git/commitdiff
staging: quatech_usb2: Potential lost wakeup scenario in TIOCMIWAIT
authorKautuk Consul <consul.kautuk@gmail.com>
Wed, 14 Sep 2011 03:26:21 +0000 (08:56 +0530)
committerGreg Kroah-Hartman <gregkh@suse.de>
Mon, 19 Sep 2011 17:46:18 +0000 (10:46 -0700)
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 <consul.kautuk@gmail.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
drivers/staging/quatech_usb2/quatech_usb2.c

index ca098cabc2bc8141b68aee51f3f210fbfb8a7c7a..02fafecd47738a23dc9bf40de76e59b374653e4b 100644 (file)
@@ -916,9 +916,10 @@ static int qt2_ioctl(struct tty_struct *tty,
                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 *tty,
                        /* 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 *tty,
                                (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 */