From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754662Ab1BFXqu (ORCPT ); Sun, 6 Feb 2011 18:46:50 -0500 Received: from 1wt.eu ([62.212.114.60]:60321 "EHLO 1wt.eu" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754470Ab1BFXq2 (ORCPT ); Sun, 6 Feb 2011 18:46:28 -0500 Message-Id: <20110206232253.463757617@pcw.home.local> User-Agent: quilt/0.48-1 Date: Mon, 07 Feb 2011 00:23:14 +0100 From: Willy Tarreau To: linux-kernel@vger.kernel.org, stable@kernel.org, stable-review@kernel.org Cc: Anton Blanchard , Amit Shah , Rusty Russell , Greg Kroah-Hartman , Willy Tarreau Subject: [PATCH 22/23] hvc_console: Fix race between hvc_close and hvc_remove, again In-Reply-To: <4beed4da27f06efb2c13d6ed48850634@local> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 2.6.27.58-stable review patch. If anyone has any objections, please let us know. ------------------ From: Anton Blanchard 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 Acked-by: Amit Shah Signed-off-by: Rusty Russell Signed-off-by: Greg Kroah-Hartman Signed-off-by: Willy Tarreau --- 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);