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Date: Wed, 17 Aug 2011 10:26:00 +0200
From: Jiri Slaby <jirislaby@...il.com>
To: Jiri Slaby <jslaby@...e.cz>
CC: gregkh@...e.de, linux-kernel@...r.kernel.org,
Alan Cox <alan@...ux.intel.com>,
"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 1/1] TTY: pty, fix pty counting
Hi, any comments on this?
On 08/10/2011 02:59 PM, Jiri Slaby wrote:
> 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@...e.cz>
> Cc: Greg KH <gregkh@...e.de>
> Cc: Alan Cox <alan@...ux.intel.com>
> Cc: "H. Peter Anvin" <hpa@...or.com>
> ---
> drivers/tty/pty.c | 17 +++++++++++++++--
> drivers/tty/tty_io.c | 3 +--
> include/linux/tty.h | 2 ++
> include/linux/tty_driver.h | 3 +++
> 4 files changed, 21 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/tty/pty.c b/drivers/tty/pty.c
> index 98b6e3b..e809e9d 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 150e4f7..4f1fc81 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 6d5eceb..a7720a4 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 9deeac8..ecdaeb9 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);
--
js
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