From: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date: Wed, 9 Sep 2015 17:16:50 +0000 (-0400)
Subject: Disable sys_membarrier
X-Git-Tag: v0.7.15~1
X-Git-Url: http://git.liburcu.org/?p=userspace-rcu.git;a=commitdiff_plain;h=de07ab9691f011d2458be8c1239d62aaa6cb6100

Disable sys_membarrier

sys_membarrier underwent changes between its original implementation and
its upcoming inclusion into the Linux kernel. Disable it to ensure we
do not use the ABI incorrectly.

Should the prior user-space code be built against a kernel header that
defines SYS_membarrier, and executed against that kernel, the following
scenarios may happen:

- -1 will be returned with EINVAL errno if the 2nd argument (flags) is
  non-zero (the previous ABI expected a single argument),
- (MEMBARRIER_EXPEDITED | MEMBARRIER_QUERY) defined as
  (1 << 0) | (1 << 16) will return -1 with EINVAL errno, because valid
  commands are now one-hot.

Therefore, should an incompatible user-space code try to use
sys_membarrier, it will simply think that the system does not have
membarrier support due to the negative return value upon query.

Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
---

diff --git a/urcu/map/urcu.h b/urcu/map/urcu.h
index dd7a691..3fae95f 100644
--- a/urcu/map/urcu.h
+++ b/urcu/map/urcu.h
@@ -48,19 +48,13 @@
 #define RCU_MB
 #endif
 
+/*
+ * The ABI of sys_membarrier changed after its original implementation.
+ * Disable it for now. Use RCU_MB flavor instead.
+ */
 #ifdef RCU_MEMBARRIER
-#include <syscall.h>
-
-/* If the headers do not support SYS_membarrier, statically use RCU_MB */
-#ifdef SYS_membarrier
-# define MEMBARRIER_EXPEDITED		(1 << 0)
-# define MEMBARRIER_DELAYED		(1 << 1)
-# define MEMBARRIER_QUERY		(1 << 16)
-# define membarrier(...)		syscall(SYS_membarrier, __VA_ARGS__)
-#else
-# undef RCU_MEMBARRIER
-# define RCU_MB
-#endif
+#undef RCU_MEMBARRIER
+#define RCU_MB
 #endif
 
 #ifdef RCU_MEMBARRIER
diff --git a/urcu/static/urcu.h b/urcu/static/urcu.h
index 5b9ceec..fc70717 100644
--- a/urcu/static/urcu.h
+++ b/urcu/static/urcu.h
@@ -60,19 +60,13 @@ extern "C" {
 #define RCU_MB
 #endif
 
+/*
+ * The ABI of sys_membarrier changed after its original implementation.
+ * Disable it for now. Use RCU_MB flavor instead.
+ */
 #ifdef RCU_MEMBARRIER
-#include <syscall.h>
-
-/* If the headers do not support SYS_membarrier, statically use RCU_MB */
-#ifdef SYS_membarrier
-# define MEMBARRIER_EXPEDITED		(1 << 0)
-# define MEMBARRIER_DELAYED		(1 << 1)
-# define MEMBARRIER_QUERY		(1 << 16)
-# define membarrier(...)		syscall(SYS_membarrier, __VA_ARGS__)
-#else
-# undef RCU_MEMBARRIER
-# define RCU_MB
-#endif
+#undef RCU_MEMBARRIER
+#define RCU_MB
 #endif
 
 /*