watchdog: new definitions and variables, initialization

The hardlockup and softockup had always been tied together.  Due to the
request of KVM folks, they had a need to have one enabled but not the
other.  Internally rework the code to split things apart more cleanly.

There is a bunch of churn here, but the end result should be code that
should be easier to maintain and fix without knowing the internals of what
is going on.

This patch (of 9):

Introduce new definitions and variables to separate the user interface in
/proc/sys/kernel from the internal run state of the lockup detectors.  The
internal run state is represented by two bits in a new variable that is
named 'watchdog_enabled'.  This helps simplify the code, for example:

- In order to check if any of the two lockup detectors is enabled,
  it is sufficient to check if 'watchdog_enabled' is not zero.

- In order to enable/disable one or both lockup detectors,
  it is sufficient to set/clear one or both bits in 'watchdog_enabled'.

- Concurrent updates of 'watchdog_enabled' need not be synchronized via
  a spinlock or a mutex. Updates can either be atomic or concurrency can
  be detected by using 'cmpxchg'.

Signed-off-by: Ulrich Obergfell <uobergfe@redhat.com>
Signed-off-by: Don Zickus <dzickus@redhat.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 2 insertions, 0 deletions

diff --git a/include/linux/nmi.h b/include/linux/nmi.h
index 9b2022ab4d85..3885a7d12bd2 100644
--- a/include/linux/nmi.h
+++ b/include/linux/nmi.h
@@ -68,6 +68,8 @@ static inline bool trigger_allbutself_cpu_backtrace(void)
 #ifdef CONFIG_LOCKUP_DETECTOR
 int hw_nmi_is_cpu_stuck(struct pt_regs *);
 u64 hw_nmi_get_sample_period(int watchdog_thresh);
+extern int nmi_watchdog_enabled;
+extern int soft_watchdog_enabled;
 extern int watchdog_user_enabled;
 extern int watchdog_thresh;
 extern int sysctl_softlockup_all_cpu_backtrace;