[31/49] hvc_console: Fix race between hvc_close and hvc_remove, again

From: Greg KH
Date: Wed Jan 05 2011 - 18:06:47 EST

2.6.32-longterm review patch. If anyone has any objections, please let us know.


From: Anton Blanchard <anton@xxxxxxxxx>

commit 320718ee074acce5ffced6506cb51af1388942aa upstream.

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);
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:


if (--hp->count == 0) {
/* Put the ref obtained in hvc_open() */


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@xxxxxxxxx>
Acked-by: Amit Shah <amit.shah@xxxxxxxxxx>
Signed-off-by: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

drivers/char/hvc_console.c | 4 ----
1 file changed, 4 deletions(-)

--- a/drivers/char/hvc_console.c
+++ b/drivers/char/hvc_console.c
@@ -367,16 +367,12 @@ static void hvc_close(struct tty_struct
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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