Commit a1ee1932 authored Mar 17, 2016 by Joshua Hunt Committed by Linus Torvalds Mar 17, 2016

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



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 <johunt@akamai.com>
Acked-by: Don Zickus <dzickus@redhat.com>
Reviewed-by: Aaron Tomlin <atomlin@redhat.com>
Cc: Ulrich Obergfell <uobergfe@redhat.com>
Cc: <stable@vger.kernel.org>	[4.1.x+]
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

parent 4c11e554

kernel/watchdog.c

+8 −1

Original line number	Diff line number	Diff line
		@@ -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) {