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hvc_console: Fix race between hvc_close and hvc_remove

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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 <anton@samba.org>
Acked-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>
This commit is contained in:
Anton Blanchard 2010-04-06 21:42:38 +10:00 committed by Rusty Russell
parent b7a413015d
commit 320718ee07
1 changed files with 0 additions and 4 deletions
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4
drivers/char/hvc_console.c
View file

@ -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);