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| author | Jiri Slaby <jslaby@suse.cz> | 2011-08-10 16:59:28 +0400 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@suse.de> | 2011-08-23 21:10:38 +0400 |
| commit | 24d406a6bf736f7aebdc8fa0f0ec86e0890c6d24 (patch) | |
| tree | 3dfb2053f7785508304fd29d6c1bb6e6a42a7d5c /drivers/tty/pty.c | |
| parent | dbb3b1ca5609d1f3848cd387d06cc60aaacf7f98 (diff) | |
| download | linux-24d406a6bf736f7aebdc8fa0f0ec86e0890c6d24.tar.xz | |
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 <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>
Diffstat (limited to 'drivers/tty/pty.c')
| -rw-r--r-- | drivers/tty/pty.c | 17 |
1 files changed, 15 insertions, 2 deletions
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 = { |