docs: static initialization of spinlocks is OK

UPDATE March 21 2005 Amit Gud <gud@eth.net>

SPIN_LOCK_UNLOCKED and RW_LOCK_UNLOCKED defeat lockdep state tracking and

are hence deprecated.

Macros SPIN_LOCK_UNLOCKED and RW_LOCK_UNLOCKED are deprecated and will be

removed soon. So for any new code dynamic initialization should be used:

Please use DEFINE_SPINLOCK()/DEFINE_RWLOCK() or

__SPIN_LOCK_UNLOCKED()/__RW_LOCK_UNLOCKED() as appropriate for static

initialization.

Dynamic initialization, when necessary, may be performed as

demonstrated below.

   spinlock_t xxx_lock;

   rwlock_t xxx_rw_lock;

   module_init(xxx_init);

Reasons for deprecation

  - it hurts automatic lock validators

  - it becomes intrusive for the realtime preemption patches

Following discussion is still valid, however, with the dynamic initialization

of spinlocks instead of static.

The following discussion is still valid, however, with the dynamic

initialization of spinlocks or with DEFINE_SPINLOCK, etc., used

instead of SPIN_LOCK_UNLOCKED.

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