From a38df1a01320298198c7cb2e3e8a61fc54459d6a Mon Sep 17 00:00:00 2001 From: Jiri Slaby Date: Wed, 10 Aug 2011 14:59:28 +0200 Subject: TTY: pty, fix pty counting commit 24d406a6bf736f7aebdc8fa0f0ec86e0890c6d24 upstream. tty_operations->remove is normally called like: queue_release_one_tty ->tty_shutdown ->tty_driver_remove_tty ->tty_operations->remove However tty_shutdown() is called from queue_release_one_tty() only if tty_operations->shutdown is NULL. But for pty, it is not. pty_unix98_shutdown() is used there as ->shutdown. So tty_operations->remove of pty (i.e. pty_unix98_remove()) is never called. This results in invalid pty_count. I.e. what can be seen in /proc/sys/kernel/pty/nr. I see this was already reported at: https://lkml.org/lkml/2009/11/5/370 But it was not fixed since then. This patch is kind of a hackish way. The problem lies in ->install. We allocate there another tty (so-called tty->link). So ->install is called once, but ->remove twice, for both tty and tty->link. The fix here is to count both tty and tty->link and divide the count by 2 for user. And to have ->remove called, let's make tty_driver_remove_tty() global and call that from pty_unix98_shutdown() (tty_operations->shutdown). While at it, let's document that when ->shutdown is defined, tty_shutdown() is not called. Signed-off-by: Jiri Slaby Cc: Alan Cox Cc: "H. Peter Anvin" Signed-off-by: Greg Kroah-Hartman --- include/linux/tty.h | 2 ++ include/linux/tty_driver.h | 3 +++ 2 files changed, 5 insertions(+) (limited to 'include') diff --git a/include/linux/tty.h b/include/linux/tty.h index d6f05292e456..6660c41949ba 100644 --- a/include/linux/tty.h +++ b/include/linux/tty.h @@ -420,6 +420,8 @@ extern void tty_driver_flush_buffer(struct tty_struct *tty); extern void tty_throttle(struct tty_struct *tty); extern void tty_unthrottle(struct tty_struct *tty); extern int tty_do_resize(struct tty_struct *tty, struct winsize *ws); +extern void tty_driver_remove_tty(struct tty_driver *driver, + struct tty_struct *tty); extern void tty_shutdown(struct tty_struct *tty); extern void tty_free_termios(struct tty_struct *tty); extern int is_current_pgrp_orphaned(void); diff --git a/include/linux/tty_driver.h b/include/linux/tty_driver.h index 9deeac855240..ecdaeb98b293 100644 --- a/include/linux/tty_driver.h +++ b/include/linux/tty_driver.h @@ -47,6 +47,9 @@ * * This routine is called synchronously when a particular tty device * is closed for the last time freeing up the resources. + * Note that tty_shutdown() is not called if ops->shutdown is defined. + * This means one is responsible to take care of calling ops->remove (e.g. + * via tty_driver_remove_tty) and releasing tty->termios. * * * void (*cleanup)(struct tty_struct * tty); -- cgit v1.2.3