From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932971AbcDJTLA (ORCPT ); Sun, 10 Apr 2016 15:11:00 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:54099 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932830AbcDJTJP (ORCPT ); Sun, 10 Apr 2016 15:09:15 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Josh Hunt , Don Zickus , Aaron Tomlin , Ulrich Obergfell , Andrew Morton , Linus Torvalds Subject: [PATCH 4.4 128/210] watchdog: dont run proc_watchdog_update if new value is same as old Date: Sun, 10 Apr 2016 11:35:49 -0700 Message-Id: <20160410183531.184634357@linuxfoundation.org> X-Mailer: git-send-email 2.8.0 In-Reply-To: <20160410183526.651820045@linuxfoundation.org> References: <20160410183526.651820045@linuxfoundation.org> User-Agent: quilt/0.64 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.4-stable review patch. If anyone has any objections, please let me know. ------------------ From: Joshua Hunt commit a1ee1932aa6bea0bb074f5e3ced112664e4637ed upstream. While working on a script to restore all sysctl params before a series of tests I found that writing any value into the /proc/sys/kernel/{nmi_watchdog,soft_watchdog,watchdog,watchdog_thresh} causes them to call proc_watchdog_update(). NMI watchdog: enabled on all CPUs, permanently consumes one hw-PMU counter. NMI watchdog: enabled on all CPUs, permanently consumes one hw-PMU counter. NMI watchdog: enabled on all CPUs, permanently consumes one hw-PMU counter. NMI watchdog: enabled on all CPUs, permanently consumes one hw-PMU counter. There doesn't appear to be a reason for doing this work every time a write occurs, so only do it when the values change. Signed-off-by: Josh Hunt Acked-by: Don Zickus Reviewed-by: Aaron Tomlin Cc: Ulrich Obergfell Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Greg Kroah-Hartman --- kernel/watchdog.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -907,6 +907,9 @@ static int proc_watchdog_common(int whic * both lockup detectors are disabled if proc_watchdog_update() * returns an error. */ + if (old == new) + goto out; + err = proc_watchdog_update(); } out: @@ -951,7 +954,7 @@ int proc_soft_watchdog(struct ctl_table int proc_watchdog_thresh(struct ctl_table *table, int write, void __user *buffer, size_t *lenp, loff_t *ppos) { - int err, old; + int err, old, new; get_online_cpus(); mutex_lock(&watchdog_proc_mutex); @@ -971,6 +974,10 @@ int proc_watchdog_thresh(struct ctl_tabl /* * Update the sample period. Restore on failure. */ + new = ACCESS_ONCE(watchdog_thresh); + if (old == new) + goto out; + set_sample_period(); err = proc_watchdog_update(); if (err) {