watchdog: Fix disable/enable regression

commit 3935e89505a1c3ab3f3b0c7ef0eae54124f48905 upstream.

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

Signed-off-by: Bjørn Mork <bjorn@mork.no>
Cc: Norbert Warmuth <nwarmuth@t-online.de>
Cc: Joseph Salisbury <joseph.salisbury@canonical.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/kernel/watchdog.c b/kernel/watchdog.c
index c8c21be11ab48e25569b43a31aee148d7d89c6d1..762081c1dcb73fb34eff2f213a6d3c9c65dfe13c 100644 (file)
--- a/kernel/watchdog.c
+++ b/kernel/watchdog.c
@@ -343,6 +343,10 @@ 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;
@@ -351,10 +355,6 @@ 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(get_sample_period()),
                      HRTIMER_MODE_REL_PINNED);
@@ -368,9 +368,6 @@ 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 */