ovsrcu_set() and ovsrcu_init() look like functions, so users are
justified in expecting the arguments to be evalueated before any of
the body of ovsrcu_set or ovsrcu_init().
With ovs-atomic-pthreads, a fallback ovs-atomics implementation used
when no C11 atomics are available or with GCC older than 4.0, the
prior definitions led to nested mutex locking when the 'VALUE'
argument was an atomic_read(). This is resolved by ensuring function
argument semantics for the parameters. For non-GCC compilers this is
done with an inline function. GCC implementation of ovs-rcu does not
fix the RCU variable type, so a GCC macro needs to be used instead.
Reported-by: YAMAMOTO Takashi <yamam...@valinux.co.jp>
Signed-off-by: Jarno Rajahalme <jrajaha...@nicira.com>
---
lib/ovs-rcu.h | 25 +++++++++++++++++++++++--
1 file changed, 23 insertions(+), 2 deletions(-)
diff --git a/lib/ovs-rcu.h b/lib/ovs-rcu.h
index c3e06ad..e27dfad 100644
--- a/lib/ovs-rcu.h
+++ b/lib/ovs-rcu.h
@@ -131,6 +131,20 @@
CONST_CAST(TYPE, ovsrcu_get__(TYPE, VAR, memory_order_consume))
#define ovsrcu_get_protected(TYPE, VAR) \
CONST_CAST(TYPE, ovsrcu_get__(TYPE, VAR, memory_order_relaxed))
+
+/* 'VALUE' may be an atomic operation, which must be evaluated before
+ * any of the body of the atomic_store_explicit. Since the type of
+ * 'VAR' is not fixed, we cannot use an inline function to get
+ * function semantics for this. */
+#define ovsrcu_set__(VAR, VALUE, ORDER) \
+ ({ \
+ typeof(VAR) var__ = (VAR); \
+ typeof(VALUE) value__ = (VALUE); \
+ memory_order order__ = (ORDER); \
+ \
+ atomic_store_explicit(&var__->p, value__, order__); \
+ (void *) 0; \
+ })
#else /* not GNU C */
struct ovsrcu_pointer { ATOMIC(void *) p; };
#define OVSRCU_TYPE(TYPE) struct ovsrcu_pointer
@@ -147,6 +161,13 @@ ovsrcu_get__(const struct ovsrcu_pointer *pointer,
memory_order order)
CONST_CAST(TYPE, ovsrcu_get__(VAR, memory_order_consume))
#define ovsrcu_get_protected(TYPE, VAR) \
CONST_CAST(TYPE, ovsrcu_get__(VAR, memory_order_relaxed))
+
+static inline void ovsrcu_set__(struct ovsrcu_pointer *pointer,
+ const void *value,
+ memory_order order)
+{
+ atomic_store_explicit(&pointer->p, CONST_CAST(void *, value), order);
+}
#endif
/* Writes VALUE to the RCU-protected pointer whose address is VAR.
@@ -154,13 +175,13 @@ ovsrcu_get__(const struct ovsrcu_pointer *pointer,
memory_order order)
* Users require external synchronization (e.g. a mutex). See "Usage" above
* for an example. */
#define ovsrcu_set(VAR, VALUE) \
- atomic_store_explicit(&(VAR)->p, VALUE, memory_order_release)
+ ovsrcu_set__(VAR, VALUE, memory_order_release)
/* This can be used for initializing RCU pointers before any readers can
* see them. A later ovsrcu_set() needs to make the bigger structure this
* is part of visible to the readers. */
#define ovsrcu_init(VAR, VALUE) \
- atomic_store_explicit(&(VAR)->p, VALUE, memory_order_relaxed)
+ ovsrcu_set__(VAR, VALUE, memory_order_relaxed)
/* Calls FUNCTION passing ARG as its pointer-type argument following the next
* grace period. See "Usage" above for example. */
--
1.7.10.4
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