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TTY: pty, fix pty counting

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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 <jslaby@suse.cz>
Cc: Alan Cox <alan@linux.intel.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
This commit is contained in:
Jiri Slaby 2011-08-10 14:59:28 +02:00 committed by Greg Kroah-Hartman
parent dbb3b1ca56
commit 24d406a6bf
4 changed files with 21 additions and 4 deletions
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17
drivers/tty/pty.c
View file

@ -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 @@ static int pty_unix98_install(struct tty_driver *driver, struct tty_struct *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 = {

3
drivers/tty/tty_io.c
View file

@ -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);

2
include/linux/tty.h
View file

@ -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);

3
include/linux/tty_driver.h
View file

@ -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);