tty: Wait interruptibly for tty lock on reopen

Allow a signal to interrupt the wait for a tty reopen; eg., if
the tty has starting final close and is waiting for the device to
drain.

Signed-off-by: Peter Hurley <peter@hurleysoftware.com>
Cc: stable <stable@vger.kernel.org> # 4.4
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

3 files changed, 16 insertions, 1 deletions

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 892c92354745..765935b144d6 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -2065,7 +2065,12 @@ retry_open:
 
                 if (tty) {
                         mutex_unlock(&tty_mutex);
-                        tty_lock(tty);
+                        retval = tty_lock_interruptible(tty);
+                        if (retval) {
+                                if (retval == -EINTR)
+                                        retval = -ERESTARTSYS;
+                                goto err_unref;
+                        }
                         /* safe to drop the kref from tty_driver_lookup_tty() */
                         tty_kref_put(tty);
                         retval = tty_reopen(tty);
@@ -2152,6 +2157,7 @@ retry_open:
         return 0;
 err_unlock:
         mutex_unlock(&tty_mutex);
+err_unref:
         /* after locks to avoid deadlock */
         if (!IS_ERR_OR_NULL(driver))
                 tty_driver_kref_put(driver);
diff --git a/drivers/tty/tty_mutex.c b/drivers/tty/tty_mutex.c
index 77703a391207..d2f3c4cd697f 100644
--- a/drivers/tty/tty_mutex.c
+++ b/drivers/tty/tty_mutex.c
@@ -19,6 +19,14 @@ void __lockfunc tty_lock(struct tty_struct *tty)
 }
 EXPORT_SYMBOL(tty_lock);
 
+int tty_lock_interruptible(struct tty_struct *tty)
+{
+        if (WARN(tty->magic != TTY_MAGIC, "L Bad %p\n", tty))
+                return -EIO;
+        tty_kref_get(tty);
+        return mutex_lock_interruptible(&tty->legacy_mutex);
+}
+
 void __lockfunc tty_unlock(struct tty_struct *tty)
 {
         if (WARN(tty->magic != TTY_MAGIC, "U Bad %p\n", tty))
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 2fd8708ea888..d9fb4b043f56 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -649,6 +649,7 @@ extern long vt_compat_ioctl(struct tty_struct *tty,
 /* tty_mutex.c */
 /* functions for preparation of BKL removal */
 extern void __lockfunc tty_lock(struct tty_struct *tty);
+extern int  tty_lock_interruptible(struct tty_struct *tty);
 extern void __lockfunc tty_unlock(struct tty_struct *tty);
 extern void __lockfunc tty_lock_slave(struct tty_struct *tty);
 extern void __lockfunc tty_unlock_slave(struct tty_struct *tty);