tty: never hold BTM while getting tty_mutex

tty_mutex is never taken with the BTM held, except for
two corner cases that are worked around here.
We give up the BTM before calling tty_release() in the
error path of tty_open().
Similarly, we reorder the locking in ptmx_open()
to get tty_mutex before the BTM.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/char/pty.c b/drivers/char/pty.c
index 622e21c..de22ea9 100644 (file)
--- a/drivers/char/pty.c
+++ b/drivers/char/pty.c
@@ -647,7 +647,7 @@ static const struct tty_operations pty_unix98_ops = {
  *             allocated_ptys_lock handles the list of free pty numbers
  */
 
-static int __ptmx_open(struct inode *inode, struct file *filp)
+static int ptmx_open(struct inode *inode, struct file *filp)
 {
        struct tty_struct *tty;
        int retval;
@@ -656,11 +656,14 @@ static int __ptmx_open(struct inode *inode, struct file *filp)
        nonseekable_open(inode, filp);
 
        /* find a device that is not in use. */
+       tty_lock();
        index = devpts_new_index(inode);
+       tty_unlock();
        if (index < 0)
                return index;
 
        mutex_lock(&tty_mutex);
+       tty_lock();
        tty = tty_init_dev(ptm_driver, index, 1);
        mutex_unlock(&tty_mutex);
 
@@ -678,24 +681,19 @@ static int __ptmx_open(struct inode *inode, struct file *filp)
                goto out1;
 
        retval = ptm_driver->ops->open(tty, filp);
-       if (!retval)
-               return 0;
+       if (retval)
+               goto out2;
 out1:
+       tty_unlock();
+       return retval;
+out2:
+       tty_unlock();
        tty_release(inode, filp);
        return retval;
 out:
        devpts_kill_index(inode, index);
-       return retval;
-}
-
-static int ptmx_open(struct inode *inode, struct file *filp)
-{
-       int ret;
-
-       tty_lock();
-       ret = __ptmx_open(inode, filp);
        tty_unlock();
-       return ret;
+       return retval;
 }
 
 static struct file_operations ptmx_fops;

diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index 5ee9081..bb22cf4 100644 (file)
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -1866,19 +1866,19 @@ got_driver:
                printk(KERN_DEBUG "error %d in opening %s...", retval,
                       tty->name);
 #endif
+               tty_unlock(); /* need to call tty_release without BTM */
                tty_release(inode, filp);
-               if (retval != -ERESTARTSYS) {
-                       tty_unlock();
+               if (retval != -ERESTARTSYS)
                        return retval;
-               }
-               if (signal_pending(current)) {
-                       tty_unlock();
+
+               if (signal_pending(current))
                        return retval;
-               }
+
                schedule();
                /*
                 * Need to reset f_op in case a hangup happened.
                 */
+               tty_lock();
                if (filp->f_op == &hung_up_tty_fops)
                        filp->f_op = &tty_fops;
                tty_unlock();