From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751819AbaANVEU (ORCPT ); Tue, 14 Jan 2014 16:04:20 -0500 Received: from mail.windriver.com ([147.11.1.11]:56683 "EHLO mail.windriver.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751367AbaANVER (ORCPT ); Tue, 14 Jan 2014 16:04:17 -0500 From: Paul Gortmaker To: Greg Kroah-Hartman , Jiri Slaby CC: , Paul Gortmaker , , Rusty Russell Subject: [PATCH] hvc: ensure hvc_init is only ever called once in hvc_console.c Date: Tue, 14 Jan 2014 16:03:37 -0500 Message-ID: <1389733436-4661-1-git-send-email-paul.gortmaker@windriver.com> X-Mailer: git-send-email 1.8.5.2 MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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: stable@vger.kernel.org # v2.6.24+ 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 --- [Greg: I realize tty-next is closed; given that this is an ancient bug, I don't see any real urgency here, so feel free to queue it whenever/whereever is most convenient - assuming it is an OK fix.] drivers/tty/hvc/hvc_console.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/drivers/tty/hvc/hvc_console.c b/drivers/tty/hvc/hvc_console.c index 9eba119bcdd3..620da5f88e91 100644 --- 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 @@ -851,7 +855,7 @@ struct hvc_struct *hvc_alloc(uint32_t vtermno, int data, 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); -- 1.8.5.2