PREEMPT_DISABLE_OFFSET
#define PREEMPT_LOCK_OFFSET PREEMPT_DISABLE_OFFSET
#define in_atomic_preempt_off() (preempt_count() != PREEMPT_DISABLE_OFFSET)
#define PREEMPT_DISABLED (PREEMPT_DISABLE_OFFSET + PREEMPT_ENABLED)
#define FORK_PREEMPT_COUNT (2*PREEMPT_DISABLE_OFFSET + PREEMPT_ENABLED)
if (WARN_ONCE(preempt_count() != 2*PREEMPT_DISABLE_OFFSET,