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author | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2017-04-20 02:20:07 +0300 |
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committer | Paul E. McKenney <paulmck@linux.vnet.ibm.com> | 2017-06-08 18:25:29 +0300 |
commit | 6016ffc3874d3a1ddf41518481da54b4714717af (patch) | |
tree | 3746c96e1cfffb9d5f740082ddff6e9454230680 /include/linux/spinlock.h | |
parent | 79269ee3fa1da52f392f8a4ebf3082152c1c8c58 (diff) | |
download | linux-6016ffc3874d3a1ddf41518481da54b4714717af.tar.xz |
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 <paulmck@linux.vnet.ibm.com>
Acked-by: Peter Zijlstra <peterz@infradead.org>
Diffstat (limited to 'include/linux/spinlock.h')
-rw-r--r-- | include/linux/spinlock.h | 20 |
1 files changed, 20 insertions, 0 deletions
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); |