The patch titled
Subject: watchdog: don't run proc_watchdog_update if new value is same as old
has been added to the -mm tree. Its filename is
watchdog-dont-run-proc_watchdog_update-if-new-value-is-same-as-old.patch
This patch should soon appear at
http://ozlabs.org/~akpm/mmots/broken-out/watchdog-dont-run-proc_watchdog_update-if-new-value-is-same-as-old.patch
and later at
http://ozlabs.org/~akpm/mmotm/broken-out/watchdog-dont-run-proc_watchdog_update-if-new-value-is-same-as-old.patch
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------------------------------------------------------
From: Joshua Hunt <johunt@xxxxxxxxxx>
Subject: 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(). Not only that, but when I
wrote to these proc files in a loop I could easily trigger a soft lockup.
[ 955.756196] NMI watchdog: enabled on all CPUs, permanently consumes one hw-PMU counter.
[ 955.765994] NMI watchdog: enabled on all CPUs, permanently consumes one hw-PMU counter.
[ 955.774619] NMI watchdog: enabled on all CPUs, permanently consumes one hw-PMU counter.
[ 955.783182] NMI watchdog: enabled on all CPUs, permanently consumes one hw-PMU counter.
[ 959.788319] NMI watchdog: BUG: soft lockup - CPU#4 stuck for 30s! [swapper/4:0]
[ 959.788325] NMI watchdog: BUG: soft lockup - CPU#5 stuck for 30s! [swapper/5:0]
There doesn't appear to be a reason for doing this work other every time a
write occurs, so only do the work when the values change.
Signed-off-by: Josh Hunt <johunt@xxxxxxxxxx>
Cc: Ulrich Obergfell <uobergfe@xxxxxxxxxx>
Cc: Don Zickus <dzickus@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/watchdog.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff -puN kernel/watchdog.c~watchdog-dont-run-proc_watchdog_update-if-new-value-is-same-as-old kernel/watchdog.c
--- a/kernel/watchdog.c~watchdog-dont-run-proc_watchdog_update-if-new-value-is-same-as-old
+++ a/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) {
_
Patches currently in -mm which might be from johunt@xxxxxxxxxx are
block-restore-proc-partitions-to-not-display-non-partitionable-removable-devices.patch
watchdog-dont-run-proc_watchdog_update-if-new-value-is-same-as-old.patch
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