Revert "drivers:tty:pty: Fix a race causing data loss on close"

This reverts commit 33d4ae9.

Pierre-Louis writes:

	Our SOF/audio CI shows an across-the-board regression when we try v5.12-rc1,
	specifically on pause/resume tests with an interactive terminal running 'aplay
	-i' commands managed by expect to simulate the user pressing the space bar to
	pause/unpause. It turns out the processes are not longer killed and the audio
	devices remain busy (see publicly available test results listed below).

	git bisect points to commit 33d4ae9 ("drivers:tty:pty: Fix a race
	causing data loss on close"). Reverting the patch fixes the issue on all test
	devices.

	Further analysis with Corey Minyard points to a problem where a slave tty will
	not get a SIGHUP when the master is closed.

So revert this for now:

Reported-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Link: https://lore.kernel.org/r/00154592-c5ee-aaba-956e-b265473b53bc@linux.intel.com
Cc: Corey Minyard <cminyard@mvista.com>
Cc: Jiri Slaby <jirislaby@kernel.org>
Cc: Mark Brown <broonie@kernel.org>,
Fixes: 33d4ae9 ("drivers:tty:pty: Fix a race causing data loss on close")
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: gregkh

drivers/tty/pty.c

@@ -66,8 +66,7 @@ static void pty_close(struct tty_struct *tty, struct file *filp)
 	wake_up_interruptible(&tty->link->read_wait);
 	wake_up_interruptible(&tty->link->write_wait);
 	if (tty->driver->subtype == PTY_TYPE_MASTER) {
-		struct file *f;
-
+		set_bit(TTY_OTHER_CLOSED, &tty->flags);
 #ifdef CONFIG_UNIX98_PTYS
 		if (tty->driver == ptm_driver) {
 			mutex_lock(&devpts_mutex);
@@ -76,17 +75,7 @@ static void pty_close(struct tty_struct *tty, struct file *filp)
 			mutex_unlock(&devpts_mutex);
 		}
 #endif
-
-		/*
-		 * This hack is required because a program can open a
-		 * pty and redirect a console to it, but if the pty is
-		 * closed and the console is not released, then the
-		 * slave side will never close.  So release the
-		 * redirect when the master closes.
-		 */
-		f = tty_release_redirect(tty->link);
-		if (f)
-			fput(f);
+		tty_vhangup(tty->link);
 	}
 }
 

drivers/tty/tty_io.c

@@ -544,9 +544,7 @@ EXPORT_SYMBOL_GPL(tty_wakeup);
  *	@tty: tty device
  *
  *	This is available to the pty code so if the master closes, if the
- *	slave is a redirect it can release the redirect.  It returns the
- *	filp for the redirect, which must be fput when the operations on
- *	the tty are completed.
+ *	slave is a redirect it can release the redirect.
  */
 struct file *tty_release_redirect(struct tty_struct *tty)
 {
@@ -561,6 +559,7 @@ struct file *tty_release_redirect(struct tty_struct *tty)
 
 	return f;
 }
+EXPORT_SYMBOL_GPL(tty_release_redirect);
 
 /**
  *	__tty_hangup		-	actual handler for hangup events