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Commit e74d098c authored by Amit Shah's avatar Amit Shah Committed by Greg Kroah-Hartman
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hvc_console: Fix race between hvc_close and hvc_remove 



Alan pointed out a race in the code where hvc_remove is invoked. The
recent virtio_console work is the first user of hvc_remove().

Alan describes it thus:

The hvc_console assumes that a close and remove call can't occur at the
same time.

In addition tty_hangup(tty) is problematic as tty_hangup is asynchronous
itself....

So this can happen

        hvc_close                               hvc_remove
        hung up ? - no
                                                lock
                                                tty = hp->tty
                                                unlock
        lock
        hp->tty = NULL
        unlock
        notify del
        kref_put the hvc struct
        close completes
        tty is destroyed
                                                tty_hangup dead tty
                                                tty->ops will be NULL
                                                NULL->...

This patch adds some tty krefs and also converts to using tty_vhangup().

Reported-by: default avatarAlan Cox <alan@lxorguk.ukuu.org.uk>
Signed-off-by: default avatarAmit Shah <amit.shah@redhat.com>
CC: Alan Cox <alan@lxorguk.ukuu.org.uk>
CC: linuxppc-dev@ozlabs.org
CC: Rusty Russell <rusty@rustcorp.com.au>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@suse.de>
parent f157b585

drivers/char/hvc_console.c

+21 −10
Original line number Diff line number Diff line
@@ -312,6 +312,7 @@ static int hvc_open(struct tty_struct *tty, struct file * filp) 
	spin_lock_irqsave(&hp->lock, flags);

	/* Check and then increment for fast path open. */

	if (hp->count++ > 0) {

		tty_kref_get(tty);

		spin_unlock_irqrestore(&hp->lock, flags);

		hvc_kick();

		return 0;
@@ -319,7 +320,7 @@ static int hvc_open(struct tty_struct *tty, struct file * filp) 


	tty->driver_data = hp;



	hp->tty = tty;

	hp->tty = tty_kref_get(tty);



	spin_unlock_irqrestore(&hp->lock, flags);
@@ -336,6 +337,7 @@ static int hvc_open(struct tty_struct *tty, struct file * filp) 
		spin_lock_irqsave(&hp->lock, flags);

		hp->tty = NULL;

		spin_unlock_irqrestore(&hp->lock, flags);

		tty_kref_put(tty);

		tty->driver_data = NULL;

		kref_put(&hp->kref, destroy_hvc_struct);

		printk(KERN_ERR "hvc_open: request_irq failed with rc %d.\n", rc);
@@ -363,13 +365,18 @@ static void hvc_close(struct tty_struct *tty, struct file * filp) 
		return;



	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);
@@ -389,6 +396,7 @@ static void hvc_close(struct tty_struct *tty, struct file * filp) 
		spin_unlock_irqrestore(&hp->lock, flags);

	}



	tty_kref_put(tty);

	kref_put(&hp->kref, destroy_hvc_struct);

}
@@ -428,6 +436,7 @@ static void hvc_hangup(struct tty_struct *tty) 


	while(temp_open_count) {

		--temp_open_count;

		tty_kref_put(tty);

		kref_put(&hp->kref, destroy_hvc_struct);

	}

}
@@ -592,7 +601,7 @@ int hvc_poll(struct hvc_struct *hp) 
	}



	/* No tty attached, just skip */

	tty = hp->tty;

	tty = tty_kref_get(hp->tty);

	if (tty == NULL)

		goto bail;
@@ -672,6 +681,8 @@ int hvc_poll(struct hvc_struct *hp) 


		tty_flip_buffer_push(tty);

	}

	if (tty)

		tty_kref_put(tty);



	return poll_mask;

}
@@ -807,7 +818,7 @@ int hvc_remove(struct hvc_struct *hp) 
	struct tty_struct *tty;



	spin_lock_irqsave(&hp->lock, flags);

	tty = hp->tty;

	tty = tty_kref_get(hp->tty);



	if (hp->index < MAX_NR_HVC_CONSOLES)

		vtermnos[hp->index] = -1;
@@ -819,18 +830,18 @@ int hvc_remove(struct hvc_struct *hp) 
	/*

	 * We 'put' the instance that was grabbed when the kref instance

	 * was initialized using kref_init().  Let the last holder of this

	 * kref cause it to be removed, which will probably be the tty_hangup

	 * kref cause it to be removed, which will probably be the tty_vhangup

	 * below.

	 */

	kref_put(&hp->kref, destroy_hvc_struct);



	/*

	 * This function call will auto chain call hvc_hangup.  The tty should

	 * always be valid at this time unless a simultaneous tty close already

	 * cleaned up the hvc_struct.

	 * This function call will auto chain call hvc_hangup.

	 */

	if (tty)

		tty_hangup(tty);

	if (tty) {

		tty_vhangup(tty);

		tty_kref_put(tty);

	}

	return 0;

}

EXPORT_SYMBOL_GPL(hvc_remove);