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Subject[PATCH 22/23] hvc_console: Fix race between hvc_close and hvc_remove, again
2.6.27.58-stable review patch.  If anyone has any objections, please let us know.

------------------
From: Anton Blanchard <anton@samba.org>

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);
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
Signed-off-by: Willy Tarreau <w@1wt.eu>

---
drivers/char/hvc_console.c | 4 ----
1 file changed, 4 deletions(-)
Index: longterm-2.6.27/drivers/char/hvc_console.c
===================================================================
--- longterm-2.6.27.orig/drivers/char/hvc_console.c 2011-01-29 15:33:05.169065818 +0100
+++ longterm-2.6.27/drivers/char/hvc_console.c 2011-01-29 15:33:55.140065271 +0100
@@ -368,16 +368,12 @@
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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