watchdog: Fix disable/enable regression

Commit 8d4516904b39 ("watchdog: Fix CPU hotplug regression") causes an
oops or hard lockup when doing

 echo 0 > /proc/sys/kernel/nmi_watchdog
 echo 1 > /proc/sys/kernel/nmi_watchdog

and the kernel is booted with nmi_watchdog=1 (default)

Running laptop-mode-tools and disconnecting/connecting AC power will
cause this to trigger, making it a common failure scenario on laptops.

Instead of bailing out of watchdog_disable() when !watchdog_enabled we
can initialize the hrtimer regardless of watchdog_enabled status.  This
makes it safe to call watchdog_disable() in the nmi_watchdog=0 case,
without the negative effect on the enabled => disabled => enabled case.

All these tests pass with this patch:
- nmi_watchdog=1
  echo 0 > /proc/sys/kernel/nmi_watchdog
  echo 1 > /proc/sys/kernel/nmi_watchdog

- nmi_watchdog=0
  echo 0 > /sys/devices/system/cpu/cpu1/online

- nmi_watchdog=0
  echo mem > /sys/power/state

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=51661

Cc: <stable@vger.kernel.org> # v3.7
Cc: Norbert Warmuth <nwarmuth@t-online.de>
Cc: Joseph Salisbury <joseph.salisbury@canonical.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Bjørn Mork <bjorn@mork.no>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index 997c6a16ec2278969a10f251f63f237e7559d42e..75a2ab3d0b0208dfa51e40339ffd00206622732e 100644 (file)
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -344,6 +344,10 @@ static void watchdog_enable(unsigned int cpu)
 {
        struct hrtimer *hrtimer = &__raw_get_cpu_var(watchdog_hrtimer);
 
+       /* kick off the timer for the hardlockup detector */
+       hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
+       hrtimer->function = watchdog_timer_fn;
+
        if (!watchdog_enabled) {
                kthread_park(current);
                return;
@@ -352,10 +356,6 @@ static void watchdog_enable(unsigned int cpu)
        /* Enable the perf event */
        watchdog_nmi_enable(cpu);
 
-       /* kick off the timer for the hardlockup detector */
-       hrtimer_init(hrtimer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
-       hrtimer->function = watchdog_timer_fn;
-
        /* done here because hrtimer_start can only pin to smp_processor_id() */
        hrtimer_start(hrtimer, ns_to_ktime(sample_period),
                      HRTIMER_MODE_REL_PINNED);
@@ -369,9 +369,6 @@ static void watchdog_disable(unsigned int cpu)
 {
        struct hrtimer *hrtimer = &__raw_get_cpu_var(watchdog_hrtimer);
 
-       if (!watchdog_enabled)
-               return;
-
        watchdog_set_prio(SCHED_NORMAL, 0);
        hrtimer_cancel(hrtimer);
        /* disable the perf event */