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authorPaul E. McKenney <paulmck@linux.vnet.ibm.com>2017-04-20 02:20:07 +0300
committerPaul E. McKenney <paulmck@linux.vnet.ibm.com>2017-06-08 18:25:29 +0300
commit6016ffc3874d3a1ddf41518481da54b4714717af (patch)
tree3746c96e1cfffb9d5f740082ddff6e9454230680 /include/linux/spinlock.h
parent79269ee3fa1da52f392f8a4ebf3082152c1c8c58 (diff)
downloadlinux-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.h20
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);