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

[ Upstream commit a1ee1932aa6bea0bb074f5e3ced112664e4637ed ]

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>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 581a68a04c64089b847d3b76d1abc138a83bb209..f89ea713213ff60d61f1625e889c5746c03fc20e 100644 (file)
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -812,6 +812,9 @@ static int proc_watchdog_common(int which, struct ctl_table *table, int write,
                 * Update the run state of the lockup detectors.
                 * Restore 'watchdog_enabled' on failure.
                 */
+               if (old == new)
+                       goto out;
+
                err = proc_watchdog_update();
                if (err)
                        watchdog_enabled = old;
@@ -857,7 +860,7 @@ 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;
 
        mutex_lock(&watchdog_proc_mutex);
 
@@ -871,6 +874,10 @@ int proc_watchdog_thresh(struct ctl_table *table, int write,
         * Update the sample period.
         * Restore 'watchdog_thresh' on failure.
         */
+       new = ACCESS_ONCE(watchdog_thresh);
+       if (old == new)
+               goto out;
+
        set_sample_period();
        err = proc_watchdog_update();
        if (err)