From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S938218AbXGSKXJ (ORCPT ); Thu, 19 Jul 2007 06:23:09 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1763075AbXGSJ4G (ORCPT ); Thu, 19 Jul 2007 05:56:06 -0400 Received: from mail.suse.de ([195.135.220.2]:35434 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753721AbXGSJzl (ORCPT ); Thu, 19 Jul 2007 05:55:41 -0400 From: Andi Kleen References: <200707191154.642492000@suse.de> In-Reply-To: <200707191154.642492000@suse.de> To: thockin@google.com, ak@suse.de, patches@x86-64.org, linux-kernel@vger.kernel.org Subject: [PATCH] [48/58] x86_64: O_EXCL on /dev/mcelog Message-Id: <20070719095534.F0B8214E05@wotan.suse.de> Date: Thu, 19 Jul 2007 11:55:34 +0200 (CEST) Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org From: Tim Hockin Background: /dev/mcelog is a clear-on-read interface. It is currently possible for multiple users to open and read() the device. Users are protected from each other during any one read, but not across reads. Description: This patch adds support for O_EXCL to /dev/mcelog. If a user opens the device with O_EXCL, no other user may open the device (EBUSY). Likewise, any user that tries to open the device with O_EXCL while another user has the device will fail (EBUSY). Result: Applications can get exclusive access to /dev/mcelog. Applications that do not care will be unchanged. Alternatives: A simpler choice would be to only allow one open() at all, regardless of O_EXCL. Testing: I wrote an application that opens /dev/mcelog with O_EXCL and observed that any other app that tried to open /dev/mcelog would fail until the exclusive app had closed the device. Caveats: None. Signed-off-by: Tim Hockin Signed-off-by: Andi Kleen Cc: Andi Kleen Signed-off-by: Andrew Morton --- arch/x86_64/kernel/mce.c | 36 ++++++++++++++++++++++++++++++++++++ 1 file changed, 36 insertions(+) Index: linux/arch/x86_64/kernel/mce.c =================================================================== --- linux.orig/arch/x86_64/kernel/mce.c +++ linux/arch/x86_64/kernel/mce.c @@ -465,6 +465,40 @@ void __cpuinit mcheck_init(struct cpuinf * Character device to read and clear the MCE log. */ +static DEFINE_SPINLOCK(mce_state_lock); +static int open_count; /* #times opened */ +static int open_exclu; /* already open exclusive? */ + +static int mce_open(struct inode *inode, struct file *file) +{ + spin_lock(&mce_state_lock); + + if (open_exclu || (open_count && (file->f_flags & O_EXCL))) { + spin_unlock(&mce_state_lock); + return -EBUSY; + } + + if (file->f_flags & O_EXCL) + open_exclu = 1; + open_count++; + + spin_unlock(&mce_state_lock); + + return 0; +} + +static int mce_release(struct inode *inode, struct file *file) +{ + spin_lock(&mce_state_lock); + + open_count--; + open_exclu = 0; + + spin_unlock(&mce_state_lock); + + return 0; +} + static void collect_tscs(void *data) { unsigned long *cpu_tsc = (unsigned long *)data; @@ -555,6 +589,8 @@ static int mce_ioctl(struct inode *i, st } static const struct file_operations mce_chrdev_ops = { + .open = mce_open, + .release = mce_release, .read = mce_read, .ioctl = mce_ioctl, };