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 <stable@xxxxxxxxxxxxxxx> know about it. >From a1ee1932aa6bea0bb074f5e3ced112664e4637ed Mon Sep 17 00:00:00 2001 From: Joshua Hunt <johunt@xxxxxxxxxx> 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 <johunt@xxxxxxxxxx> 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@xxxxxxxxxx> Acked-by: Don Zickus <dzickus@xxxxxxxxxx> Reviewed-by: Aaron Tomlin <atomlin@xxxxxxxxxx> Cc: Ulrich Obergfell <uobergfe@xxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx> --- kernel/watchdog.c | 9 ++++++++- 1 file changed, 8 insertions(+), 1 deletion(-) --- a/kernel/watchdog.c +++ b/kernel/watchdog.c @@ -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 johunt@xxxxxxxxxx are queue-4.4/watchdog-don-t-run-proc_watchdog_update-if-new-value-is-same-as-old.patch -- To unsubscribe from this list: send the line "unsubscribe stable" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html