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    Subject[PATCH 4.5 142/238] watchdog: dont run proc_watchdog_update if new value is same as old
    Date
    4.5-stable review patch.  If anyone has any objections, please let me know.

    ------------------

    From: Joshua Hunt <johunt@akamai.com>

    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.

    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>
    Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
    Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
    Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

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

    --- a/kernel/watchdog.c
    +++ b/kernel/watchdog.c
    @@ -923,6 +923,9 @@ 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:
    @@ -967,7 +970,7 @@ 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);
    @@ -987,6 +990,10 @@ 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) {

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