Introduce smp_acquire__after_ctrl_dep(), this construct is not
uncommen, but the lack of this barrier is.
Signed-off-by: Peter Zijlstra (Intel) <pet...@infradead.org>
---
include/linux/compiler.h | 14 ++++++++++----
ipc/sem.c | 14 ++------------
2 files changed, 12 insertions(+), 16 deletions(-)
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -305,20 +305,26 @@ static __always_inline void __write_once
})
/**
+ * smp_acquire__after_ctrl_dep() - Provide ACQUIRE ordering after a control
dependency
+ *
+ * A control dependency provides a LOAD->STORE order, the additional RMB
+ * provides LOAD->LOAD order, together they provide LOAD->{LOAD,STORE} order,
+ * aka. ACQUIRE.
+ */
+#define smp_acquire__after_ctrl_dep() smp_rmb()
+
+/**
* smp_cond_acquire() - Spin wait for cond with ACQUIRE ordering
* @cond: boolean expression to wait for
*
* Equivalent to using smp_load_acquire() on the condition variable but employs
* the control dependency of the wait to reduce the barrier on many platforms.
*
- * The control dependency provides a LOAD->STORE order, the additional RMB
- * provides LOAD->LOAD order, together they provide LOAD->{LOAD,STORE} order,
- * aka. ACQUIRE.
*/
#define smp_cond_acquire(cond) do { \
while (!(cond)) \
cpu_relax(); \
- smp_rmb(); /* ctrl + rmb := acquire */ \
+ smp_acquire__after_ctrl_dep(); \
} while (0)
#endif /* __KERNEL__ */
--- a/ipc/sem.c
+++ b/ipc/sem.c
@@ -260,16 +260,6 @@ static void sem_rcu_free(struct rcu_head
}
/*
- * spin_unlock_wait() and !spin_is_locked() are not memory barriers, they
- * are only control barriers.
- * The code must pair with spin_unlock(&sem->lock) or
- * spin_unlock(&sem_perm.lock), thus just the control barrier is insufficient.
- *
- * smp_rmb() is sufficient, as writes cannot pass the control barrier.
- */
-#define ipc_smp_acquire__after_spin_is_unlocked() smp_rmb()
-
-/*
* Wait until all currently ongoing simple ops have completed.
* Caller must own sem_perm.lock.
* New simple ops cannot start, because simple ops first check
@@ -292,7 +282,7 @@ static void sem_wait_array(struct sem_ar
sem = sma->sem_base + i;
spin_unlock_wait(&sem->lock);
}
- ipc_smp_acquire__after_spin_is_unlocked();
+ smp_acquire__after_ctrl_dep();
}
/*
@@ -350,7 +340,7 @@ static inline int sem_lock(struct sem_ar
* complex_count++;
* spin_unlock(sem_perm.lock);
*/
- ipc_smp_acquire__after_spin_is_unlocked();
+ smp_acquire__after_ctrl_dep();
/*
* Now repeat the test of complex_count:
