From: Jiri Slaby Date: Wed, 10 Aug 2011 12:59:28 +0000 (+0200) Subject: TTY: pty, fix pty counting X-Git-Url: http://git.lede-project.org./?a=commitdiff_plain;h=24d406a6bf736f7aebdc8fa0f0ec86e0890c6d24;p=openwrt%2Fstaging%2Fblogic.git 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 --- 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 = { diff --git a/drivers/tty/tty_io.c b/drivers/tty/tty_io.c index 150e4f747c7d..4f1fc81112e6 100644 --- a/drivers/tty/tty_io.c +++ b/drivers/tty/tty_io.c @@ -1295,8 +1295,7 @@ static int tty_driver_install_tty(struct tty_driver *driver, * * Locking: tty_mutex for now */ -static void tty_driver_remove_tty(struct tty_driver *driver, - struct tty_struct *tty) +void tty_driver_remove_tty(struct tty_driver *driver, struct tty_struct *tty) { if (driver->ops->remove) driver->ops->remove(driver, tty); diff --git a/include/linux/tty.h b/include/linux/tty.h index 44bc0c5617e1..5f2ede82b3d6 100644 --- a/include/linux/tty.h +++ b/include/linux/tty.h @@ -421,6 +421,8 @@ 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);