From 24d406a6bf736f7aebdc8fa0f0ec86e0890c6d24 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 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" Cc: stable Signed-off-by: Greg Kroah-Hartman --- drivers/tty/pty.c | 17 +++++++++++++++-- 1 file changed, 15 insertions(+), 2 deletions(-) (limited to 'drivers/tty/pty.c') diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c index 98b6e3bdb000..e809e9d4683c 100644 --- a/drivers/tty/pty.c +++ b/drivers/tty/pty.c @@ -446,8 +446,19 @@ static inline void legacy_pty_init(void) { } int pty_limit = NR_UNIX98_PTY_DEFAULT; static int pty_limit_min; static int pty_limit_max = NR_UNIX98_PTY_MAX; +static int tty_count; static int pty_count; +static inline void pty_inc_count(void) +{ + pty_count = (++tty_count) / 2; +} + +static inline void pty_dec_count(void) +{ + pty_count = (--tty_count) / 2; +} + static struct cdev ptmx_cdev; static struct ctl_table pty_table[] = { @@ -542,6 +553,7 @@ static struct tty_struct *pts_unix98_lookup(struct tty_driver *driver, static void pty_unix98_shutdown(struct tty_struct *tty) { + tty_driver_remove_tty(tty->driver, tty); /* We have our own method as we don't use the tty index */ kfree(tty->termios); } @@ -588,7 +600,8 @@ static int pty_unix98_install(struct tty_driver *driver, struct tty_struct *tty) */ tty_driver_kref_get(driver); tty->count++; - pty_count++; + pty_inc_count(); /* tty */ + pty_inc_count(); /* tty->link */ return 0; err_free_mem: deinitialize_tty_struct(o_tty); @@ -602,7 +615,7 @@ err_free_tty: static void pty_unix98_remove(struct tty_driver *driver, struct tty_struct *tty) { - pty_count--; + pty_dec_count(); } static const struct tty_operations ptm_unix98_ops = { -- cgit v1.2.3