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

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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>
This commit is contained in:
Joshua Hunt 2016-03-17 14:17:23 -07:00 committed by Linus Torvalds
parent 4c11e554fb
commit a1ee1932aa
1 changed files with 8 additions and 1 deletions
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9
kernel/watchdog.c
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@ -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) {