From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754322AbaD1BbI (ORCPT ); Sun, 27 Apr 2014 21:31:08 -0400 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:42983 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752687AbaD1B3W (ORCPT ); Sun, 27 Apr 2014 21:29:22 -0400 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, "Jim Somerville" , "Greg Kroah-Hartman" , "Rusty Russell" , "Paul Gortmaker" Date: Mon, 28 Apr 2014 02:11:22 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.2 31/94] hvc: ensure hvc_init is only ever called once in hvc_console.c In-Reply-To: X-SA-Exim-Connect-IP: 192.168.4.249 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.2.58-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: Paul Gortmaker commit f76a1cbed18c86e2d192455f0daebb48458965f3 upstream. Commit 3e6c6f630a5282df8f3393a59f10eb9c56536d23 ("Delay creation of khcvd thread") moved the call of hvc_init from being a device_initcall into hvc_alloc, and used a non-null hvc_driver as indication of whether hvc_init had already been called. The problem with this is that hvc_driver is only assigned a value at the bottom of hvc_init, and so there is a window where multiple hvc_alloc calls can be in progress at the same time and hence try and call hvc_init multiple times. Previously the use of device_init guaranteed that hvc_init was only called once. This manifests itself as sporadic instances of two hvc_init calls racing each other, and with the loser of the race getting -EBUSY from tty_register_driver() and hence that virtual console fails: Couldn't register hvc console driver virtio-ports vport0p1: error -16 allocating hvc for port Here we add an atomic_t to guarantee we'll never run hvc_init twice. Cc: Rusty Russell Cc: Greg Kroah-Hartman Fixes: 3e6c6f630a52 ("Delay creation of khcvd thread") Reported-by: Jim Somerville Tested-by: Jim Somerville Signed-off-by: Paul Gortmaker Signed-off-by: Greg Kroah-Hartman Signed-off-by: Ben Hutchings --- drivers/tty/hvc/hvc_console.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) --- a/drivers/tty/hvc/hvc_console.c +++ b/drivers/tty/hvc/hvc_console.c @@ -31,6 +31,7 @@ #include #include #include +#include #include #include #include @@ -70,6 +71,9 @@ static struct task_struct *hvc_task; /* Picks up late kicks after list walk but before schedule() */ static int hvc_kicked; +/* hvc_init is triggered from hvc_alloc, i.e. only when actually used */ +static atomic_t hvc_needs_init __read_mostly = ATOMIC_INIT(-1); + static int hvc_init(void); #ifdef CONFIG_MAGIC_SYSRQ @@ -825,7 +829,7 @@ struct hvc_struct *hvc_alloc(uint32_t vt int i; /* We wait until a driver actually comes along */ - if (!hvc_driver) { + if (atomic_inc_not_zero(&hvc_needs_init)) { int err = hvc_init(); if (err) return ERR_PTR(err);