From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753810AbcCLXug (ORCPT ); Sat, 12 Mar 2016 18:50:36 -0500 Received: from prod-mail-xrelay07.akamai.com ([23.79.238.175]:44281 "EHLO prod-mail-xrelay07.akamai.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753748AbcCLXub (ORCPT ); Sat, 12 Mar 2016 18:50:31 -0500 From: Joshua Hunt To: akpm@linux-foundation.org, uobergfe@redhat.com, dzickus@redhat.com Cc: linux-kernel@vger.kernel.org, Joshua Hunt Subject: [PATCH] watchdog: don't run proc_watchdog_update if new value is same as old Date: Sat, 12 Mar 2016 18:50:26 -0500 Message-Id: <1457826627-21727-1-git-send-email-johunt@akamai.com> X-Mailer: git-send-email 1.7.9.5 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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(). Not only that, but when I wrote to these proc files in a loop I could easily trigger a soft lockup. [ 955.756196] NMI watchdog: enabled on all CPUs, permanently consumes one hw-PMU counter. [ 955.765994] NMI watchdog: enabled on all CPUs, permanently consumes one hw-PMU counter. [ 955.774619] NMI watchdog: enabled on all CPUs, permanently consumes one hw-PMU counter. [ 955.783182] NMI watchdog: enabled on all CPUs, permanently consumes one hw-PMU counter. [ 959.788319] NMI watchdog: BUG: soft lockup - CPU#4 stuck for 30s! [swapper/4:0] [ 959.788325] NMI watchdog: BUG: soft lockup - CPU#5 stuck for 30s! [swapper/5:0] There doesn't appear to be a reason for doing this work other every time a write occurs, so only do the work when the values change. Signed-off-by: Josh Hunt --- kernel/watchdog.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) diff --git a/kernel/watchdog.c b/kernel/watchdog.c index b3ace6e..9acb29f 100644 --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -923,6 +923,9 @@ static int proc_watchdog_common(int which, struct ctl_table *table, int write, * both lockup detectors are disabled if proc_watchdog_update() * returns an error. */ + if (old == new) + goto out; + err = proc_watchdog_update(); } out: @@ -967,7 +970,7 @@ int proc_soft_watchdog(struct ctl_table *table, int write, 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); @@ -987,6 +990,10 @@ int proc_watchdog_thresh(struct ctl_table *table, int write, /* * 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) { -- 1.7.9.5