From: Paul E. McKenney Date: Wed, 19 Apr 2017 23:20:07 +0000 (-0700) Subject: atomics: Add header comment so spin_unlock_wait() X-Git-Url: https://git.stricted.de/?a=commitdiff_plain;h=6016ffc3874d3a1ddf41518481da54b4714717af;p=GitHub%2Fmoto-9609%2Fandroid_kernel_motorola_exynos9610.git 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: Paul E. McKenney Acked-by: Peter Zijlstra --- diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h index 59248dcc6ef3..d9510e8522d4 100644 --- a/include/linux/spinlock.h +++ b/include/linux/spinlock.h @@ -369,6 +369,26 @@ static __always_inline int spin_trylock_irq(spinlock_t *lock) 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) { raw_spin_unlock_wait(&lock->rlock);