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Commit 64ba3dc3 authored by Arnd Bergmann's avatar Arnd Bergmann Committed by Greg Kroah-Hartman
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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: default avatarArnd Bergmann <arnd@arndb.de>
Cc: Alan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent ec79d605

drivers/char/pty.c

+11 −13
Original line number Diff line number Diff line
@@ -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;

drivers/char/tty_io.c

+6 −6
Original line number Diff line number Diff line
@@ -1866,19 +1866,19 @@ static int tty_open(struct inode *inode, struct file *filp) 
		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();