Commit 6016ffc3 authored by Paul E. McKenney's avatar Paul E. McKenney

atomics: Add header comment so spin_unlock_wait()

There is material describing the ordering guarantees provided by
spin_unlock_wait(), but it is not necessarily easy to find.  This commit
therefore adds a docbook header comment to this function informally
describing its semantics.
Signed-off-by: default avatarPaul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: default avatarPeter Zijlstra <peterz@infradead.org>
parent 79269ee3
...@@ -369,6 +369,26 @@ static __always_inline int spin_trylock_irq(spinlock_t *lock) ...@@ -369,6 +369,26 @@ static __always_inline int spin_trylock_irq(spinlock_t *lock)
raw_spin_trylock_irqsave(spinlock_check(lock), flags); \ raw_spin_trylock_irqsave(spinlock_check(lock), flags); \
}) })
/**
* spin_unlock_wait - Interpose between successive critical sections
* @lock: the spinlock whose critical sections are to be interposed.
*
* Semantically this is equivalent to a spin_lock() immediately
* followed by a spin_unlock(). However, most architectures have
* more efficient implementations in which the spin_unlock_wait()
* cannot block concurrent lock acquisition, and in some cases
* where spin_unlock_wait() does not write to the lock variable.
* Nevertheless, spin_unlock_wait() can have high overhead, so if
* you feel the need to use it, please check to see if there is
* a better way to get your job done.
*
* The ordering guarantees provided by spin_unlock_wait() are:
*
* 1. All accesses preceding the spin_unlock_wait() happen before
* any accesses in later critical sections for this same lock.
* 2. All accesses following the spin_unlock_wait() happen after
* any accesses in earlier critical sections for this same lock.
*/
static __always_inline void spin_unlock_wait(spinlock_t *lock) static __always_inline void spin_unlock_wait(spinlock_t *lock)
{ {
raw_spin_unlock_wait(&lock->rlock); raw_spin_unlock_wait(&lock->rlock);
......
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