tty: shutdown method

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>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/drivers/char/pty.c b/drivers/char/pty.c
index 76b27932d229df31d3ff24f7d09e83afecdb278a..ec09c1cd4fe9b6196d732715ba8b345f98fac7ae 100644 (file)
--- a/drivers/char/pty.c
+++ b/drivers/char/pty.c
@@ -388,7 +388,14 @@ 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,
@@ -397,10 +404,10 @@ 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_unix98_ioctl,
+       .shutdown = pty_shutdown
 };
 
-
 static void __init unix98_pty_init(void)
 {
        ptm_driver = alloc_tty_driver(NR_UNIX98_PTY_MAX);
@@ -427,7 +434,7 @@ 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";

diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
index 2e96ce0fddc56aacd7027342fc771b7d3d16e82f..f91704d57a4e3c288d70826c0bd717e523db86f3 100644 (file)
--- a/drivers/char/tty_io.c
+++ b/drivers/char/tty_io.c
@@ -1482,6 +1482,31 @@ 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
@@ -1499,27 +1524,11 @@ 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 ec94521c31189698e0ac83f5d23d78a2f75a4c6f..37a45db5bae080a376c37902643b9d44fcc3fbd9 100644 (file)
--- 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 e00393a3d1c9376ca2ee9f607408fcf1700c7e99..6e39c705b9b67e9b111d36cd661a8325b2166d3a 100644 (file)
--- a/include/linux/tty.h
+++ b/include/linux/tty.h
@@ -354,7 +354,8 @@ 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 ac6e58e26b73f4f9d55ab5e32a188c783dd9d3c5..2322313a8589d614c84275d020f0ad1a33d9ad41 100644 (file)
--- 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);
  *
@@ -200,6 +205,7 @@ 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);