Commit 320718ee authored by Anton Blanchard's avatar Anton Blanchard Committed by Rusty Russell

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: default avatarAnton Blanchard <anton@samba.org>
Acked-by: default avatarAmit Shah <amit.shah@redhat.com>
Signed-off-by: default avatarRusty Russell <rusty@rustcorp.com.au>
parent b7a41301
......@@ -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);
......
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