Revert "TTY: call tty_driver_lookup_tty unconditionally"

This reverts commit 631180aca723cb92e128fdac5fd144e913ca84e5.

It caused problems when /dev/tty is a pty:
	https://lkml.org/lkml/2011/10/12/401

Cc: Jiri Slaby <jslaby@suse.cz>
Cc: stable <stable@vger.kernel.org>
Cc: Sukadev Bhattiprolu <sukadev@us.ibm.com>
Cc: Alan Cox <alan@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

1 files changed, 12 insertions, 9 deletions

diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c
index 0425170d9ed6..767ecbb4761a 100644
--- a/drivers/tty/tty_io.c
+++ b/drivers/tty/tty_io.c
@@ -1821,7 +1821,7 @@ int tty_release(struct inode *inode, struct file *filp)
 
 static int tty_open(struct inode *inode, struct file *filp)
 {
-        struct tty_struct *tty;
+        struct tty_struct *tty = NULL;
         int noctty, retval;
         struct tty_driver *driver;
         int index;
@@ -1892,14 +1892,17 @@ retry_open:
                 return -ENODEV;
         }
 got_driver:
-        /* check whether we're reopening an existing tty */
-        tty = tty_driver_lookup_tty(driver, inode, index);
-        if (IS_ERR(tty)) {
-                tty_unlock();
-                mutex_unlock(&tty_mutex);
-                tty_driver_kref_put(driver);
-                tty_free_file(filp);
-                return PTR_ERR(tty);
+        if (!tty) {
+                /* check whether we're reopening an existing tty */
+                tty = tty_driver_lookup_tty(driver, inode, index);
+
+                if (IS_ERR(tty)) {
+                        tty_unlock();
+                        mutex_unlock(&tty_mutex);
+                        tty_driver_kref_put(driver);
+                        tty_free_file(filp);
+                        return PTR_ERR(tty);
+                }
         }
 
         if (tty) {