hvc_console: Fix race between hvc_close and hvc_remove

I don't claim to understand the tty layer, but it seems like hvc_open and
hvc_close should be balanced in their kref reference counting.

Right now we get a kref every call to hvc_open:

        if (hp->count++ > 0) {
                tty_kref_get(tty); <----- here
                spin_unlock_irqrestore(&hp->lock, flags);
                hvc_kick();
                return 0;
        } /* else count == 0 */

        tty->driver_data = hp;

        hp->tty = tty_kref_get(tty); <------ or here if hp->count was 0

But hvc_close has:

        tty_kref_get(tty);

        if (--hp->count == 0) {
...
                /* Put the ref obtained in hvc_open() */
                tty_kref_put(tty);
...
        }

        tty_kref_put(tty);

Since the outside kref get/put balance we only do a single kref_put when
count reaches 0.

The patch below changes things to call tty_kref_put once for every
hvc_close call, and with that my machine boots fine.

Signed-off-by: Anton Blanchard <[email protected]>
Acked-by: Amit Shah <[email protected]>
Signed-off-by: Rusty Russell <[email protected]>

diff --git a/drivers/char/hvc_console.c b/drivers/char/hvc_console.c
index d3890e8d30e11ef8ba090481b6b1175553b7dd1a..35cca4c7fb186684aa41ef27228d85a932d97774 100644 (file)
--- a/drivers/char/hvc_console.c
+++ b/drivers/char/hvc_console.c
@@ -368,16 +368,12 @@ static void hvc_close(struct tty_struct *tty, struct file * filp)
        hp = tty->driver_data;
 
        spin_lock_irqsave(&hp->lock, flags);
-       tty_kref_get(tty);
 
        if (--hp->count == 0) {
                /* We are done with the tty pointer now. */
                hp->tty = NULL;
                spin_unlock_irqrestore(&hp->lock, flags);
 
-               /* Put the ref obtained in hvc_open() */
-               tty_kref_put(tty);
-
                if (hp->ops->notifier_del)
                        hp->ops->notifier_del(hp, hp->data);