Re: [PATCH] vt: kill tty->count usage (v2)

[Alan Cox <alan@lxorguk.ukuu.org.uk>]

On Mon, 18 Aug 2008 17:04:14 -0400
Aristeu Rozanski <aris@redhat.com> wrote:

> Hi Alan,
> > > The commit e0426e6a09954d205da2d674a3d368d2715e3afd fixes a real race but
> > > still isn't enough to prevent these:
> > > 
> > > kobject_add_internal failed for vcs7 with -EEXIST, don't try to register
> > > things with the same name in the same direc.
> > 
> > Patch dropped due to testing failures.
> > 
> > Boot to run level 3, log in and type "reboot\n". Wait
> > 
> > Spews vt->driver_data == NULL warnings and oopses
> do you mind posting the logs somewhere? I wasn't able to reproduce it here so

I decided it might be better to tackle this one 'head on' and go to the
root of the problem. I've pushed the following into the stack of patches
for -next

tty: shutdown method

From: Alan Cox <alan@redhat.com>

Right now there are various drivers that try to use tty->count to know when
they get the final close. Aristeau Rozanski showed while debugging the vt
sysfs race that this isn't entirely safe.

Instead of driver side tricks to work around this introduce a shutdown which
is called when the tty is being destructed. This also means that the shutdown
method is tied into the refcounting.

Use this to rework the console close/sysfs logic.

Remove lots of special case code from the tty core code. The pty code can now
have a shutdown() method that replaces the special case hackery in the tree
free up paths.

Signed-off-by: Alan Cox <alan@redhat.com>
---

 drivers/char/pty.c         |   29 ++++++++++++++++++++++----
 drivers/char/tty_io.c      |   49 ++++++++++++++++++++++++++------------------
 drivers/char/vt.c          |   34 +++++++++++++++----------------
 include/linux/tty.h        |    3 ++-
 include/linux/tty_driver.h |    6 +++++
 5 files changed, 79 insertions(+), 42 deletions(-)


diff --git a/drivers/char/pty.c b/drivers/char/pty.c
index 76b2793..fbd215b 100644
--- a/drivers/char/pty.c
+++ b/drivers/char/pty.c
@@ -388,7 +388,27 @@ static int pty_unix98_ioctl(struct tty_struct *tty, struct file *file,
 	return -ENOIOCTLCMD;
 }
 
-static const struct tty_operations pty_unix98_ops = {
+static void pty_shutdown(struct tty_struct *tty)
+{
+	/* We have our own method as we don't use the tty index */
+	kfree(tty->termios);
+	kfree(tty->termios_locked);
+}
+
+static const struct tty_operations ptm_unix98_ops = {
+	.open = pty_open,
+	.close = pty_close,
+	.write = pty_write,
+	.write_room = pty_write_room,
+	.flush_buffer = pty_flush_buffer,
+	.chars_in_buffer = pty_chars_in_buffer,
+	.unthrottle = pty_unthrottle,
+	.set_termios = pty_set_termios,
+	.ioctl = pty_unix98_ioctl,
+	.shutdown = pty_shutdown
+};
+
+static const struct tty_operations pts_unix98_ops = {
 	.open = pty_open,
 	.close = pty_close,
 	.write = pty_write,
@@ -397,7 +417,8 @@ static const struct tty_operations pty_unix98_ops = {
 	.chars_in_buffer = pty_chars_in_buffer,
 	.unthrottle = pty_unthrottle,
 	.set_termios = pty_set_termios,
-	.ioctl = pty_unix98_ioctl
+	.ioctl = pty_bsd_ioctl,
+	.shutdown = pty_shutdown
 };
 
 
@@ -427,7 +448,7 @@ static void __init unix98_pty_init(void)
 	ptm_driver->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW |
 		TTY_DRIVER_DYNAMIC_DEV | TTY_DRIVER_DEVPTS_MEM;
 	ptm_driver->other = pts_driver;
-	tty_set_operations(ptm_driver, &pty_unix98_ops);
+	tty_set_operations(ptm_driver, &ptm_unix98_ops);
 
 	pts_driver->owner = THIS_MODULE;
 	pts_driver->driver_name = "pty_slave";
@@ -443,7 +464,7 @@ static void __init unix98_pty_init(void)
 	pts_driver->flags = TTY_DRIVER_RESET_TERMIOS | TTY_DRIVER_REAL_RAW |
 		TTY_DRIVER_DYNAMIC_DEV | TTY_DRIVER_DEVPTS_MEM;
 	pts_driver->other = ptm_driver;
-	tty_set_operations(pts_driver, &pty_ops);
+	tty_set_operations(pts_driver, &pts_unix98_ops);
 	
 	if (tty_register_driver(ptm_driver))
 		panic("Couldn't register Unix98 ptm driver");
diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index 3aabf2e..8a70cbe 100644
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -1472,6 +1472,31 @@ release_mem_out:
 	goto end_init;
 }
 
+void tty_free_termios(struct tty_struct *tty)
+{
+	struct ktermios *tp;
+	int idx = tty->index;
+	/* Kill this flag and push into drivers for locking etc */
+	if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS) {
+		/* FIXME: Locking on ->termios array */
+		tp = tty->termios;
+		tty->driver->termios[idx] = NULL;
+		kfree(tp);
+
+		tp = tty->termios_locked;
+		tty->driver->termios_locked[idx] = NULL;
+		kfree(tp);
+	}
+}
+EXPORT_SYMBOL(tty_free_termios);
+
+void tty_shutdown(struct tty_struct *tty)
+{
+	tty->driver->ttys[tty->index] = NULL;
+	tty_free_termios(tty);
+}
+EXPORT_SYMBOL(tty_shutdown);
+
 /**
  *	release_one_tty		-	release tty structure memory
  *	@kref: kref of tty we are obliterating
@@ -1489,27 +1514,11 @@ static void release_one_tty(struct kref *kref)
 {
 	struct tty_struct *tty = container_of(kref, struct tty_struct, kref);
 	struct tty_driver *driver = tty->driver;
-	int devpts = tty->driver->flags & TTY_DRIVER_DEVPTS_MEM;
-	struct ktermios *tp;
-	int idx = tty->index;
-
-	if (!devpts)
-		tty->driver->ttys[idx] = NULL;
-
-	if (tty->driver->flags & TTY_DRIVER_RESET_TERMIOS) {
-		/* FIXME: Locking on ->termios array */
-		tp = tty->termios;
-		if (!devpts)
-			tty->driver->termios[idx] = NULL;
-		kfree(tp);
-
-		tp = tty->termios_locked;
-		if (!devpts)
-			tty->driver->termios_locked[idx] = NULL;
-		kfree(tp);
-	}
-
 
+	if (tty->ops->shutdown)
+		tty->ops->shutdown(tty);
+	else
+		tty_shutdown(tty);
 	tty->magic = 0;
 	/* FIXME: locking on tty->driver->refcount */
 	tty->driver->refcount--;
diff --git a/drivers/char/vt.c b/drivers/char/vt.c
index ec94521..37a45db 100644
--- a/drivers/char/vt.c
+++ b/drivers/char/vt.c
@@ -2758,6 +2758,12 @@ static int con_open(struct tty_struct *tty, struct file *filp)
 		ret = vc_allocate(currcons);
 		if (ret == 0) {
 			struct vc_data *vc = vc_cons[currcons].d;
+
+			/* Still being freed */
+			if (vc->vc_tty) {
+				release_console_sem();
+				return -ERESTARTSYS;
+			}
 			tty->driver_data = vc;
 			vc->vc_tty = tty;
 
@@ -2787,25 +2793,18 @@ static int con_open(struct tty_struct *tty, struct file *filp)
  */
 static void con_close(struct tty_struct *tty, struct file *filp)
 {
-	mutex_lock(&tty_mutex);
-	acquire_console_sem();
-	if (tty && tty->count == 1) {
-		struct vc_data *vc = tty->driver_data;
+	/* Nothing to do - we defer to shutdown */
+}
 
-		if (vc)
-			vc->vc_tty = NULL;
-		tty->driver_data = NULL;
-		vcs_remove_sysfs(tty);
-		release_console_sem();
-		mutex_unlock(&tty_mutex);
-		/*
-		 * tty_mutex is released, but we still hold BKL, so there is
-		 * still exclusion against init_dev()
-		 */
-		return;
-	}
+static void con_shutdown(struct tty_struct *tty)
+{
+	struct vc_data *vc = tty->driver_data;
+	BUG_ON(vc == NULL);
+	acquire_console_sem();
+	vc->vc_tty = NULL;
+	vcs_remove_sysfs(tty);
 	release_console_sem();
-	mutex_unlock(&tty_mutex);
+	tty_shutdown(tty);
 }
 
 static int default_italic_color    = 2; // green (ASCII)
@@ -2930,6 +2929,7 @@ static const struct tty_operations con_ops = {
 	.throttle = con_throttle,
 	.unthrottle = con_unthrottle,
 	.resize = vt_resize,
+	.shutdown = con_shutdown
 };
 
 int __init vty_init(void)
diff --git a/include/linux/tty.h b/include/linux/tty.h
index 852484b..ee6d655 100644
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -352,7 +352,8 @@ 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 tty_struct *real_tty,
 						struct winsize *ws);
-
+extern void tty_shutdown(struct tty_struct *tty);
+extern void tty_free_termios(struct tty_struct *tty);
 extern int is_current_pgrp_orphaned(void);
 extern struct pid *tty_get_pgrp(struct tty_struct *tty);
 extern int is_ignored(int sig);
diff --git a/include/linux/tty_driver.h b/include/linux/tty_driver.h
index 16d2794..fe29dcd 100644
--- a/include/linux/tty_driver.h
+++ b/include/linux/tty_driver.h
@@ -21,6 +21,11 @@
  *
  *	Required method.
  *
+ * void (*shutdown)(struct tty_struct * tty);
+ *
+ * 	This routine is called when a particular tty device is closed for
+ *	the last time freeing up the resources.
+ *
  * int (*write)(struct tty_struct * tty,
  * 		 const unsigned char *buf, int count);
  *
@@ -192,6 +197,7 @@ struct tty_driver;
 struct tty_operations {
 	int  (*open)(struct tty_struct * tty, struct file * filp);
 	void (*close)(struct tty_struct * tty, struct file * filp);
+	void (*shutdown)(struct tty_struct *tty);
 	int  (*write)(struct tty_struct * tty,
 		      const unsigned char *buf, int count);
 	int  (*put_char)(struct tty_struct *tty, unsigned char ch);