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authorJiri Slaby <jslaby@suse.cz>2011-08-10 14:59:28 +0200
committerGreg Kroah-Hartman <gregkh@suse.de>2011-08-23 10:10:38 -0700
commit24d406a6bf736f7aebdc8fa0f0ec86e0890c6d24 (patch)
tree3dfb2053f7785508304fd29d6c1bb6e6a42a7d5c /drivers/tty/pty.c
parentdbb3b1ca5609d1f3848cd387d06cc60aaacf7f98 (diff)
downloadlinux-24d406a6bf736f7aebdc8fa0f0ec86e0890c6d24.tar.bz2
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.c17
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 = {