Patch "watchdog: don't run proc_watchdog_update if new value is same as old" has been added to the 4.4-stable tree

This is a note to let you know that I've just added the patch titled

watchdog: don't run proc_watchdog_update if new value is same as old

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
watchdog-don-t-run-proc_watchdog_update-if-new-value-is-same-as-old.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Joshua Hunt <[email protected]>
Date: Thu, 17 Mar 2016 14:17:23 -0700
Subject: watchdog: don't run proc_watchdog_update if new value is same as old

From: Joshua Hunt <[email protected]>

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.

---
 kernel/watchdog.c |    9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

@@ -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) {

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/watchdog-don-t-run-proc_watchdog_update-if-new-value-is-same-as-old.patch