From: Mathieu Desnoyers Date: Wed, 9 Sep 2015 17:16:50 +0000 (-0400) Subject: Disable sys_membarrier X-Git-Tag: v0.8.8~1 X-Git-Url: https://git.lttng.org./?a=commitdiff_plain;h=eaaff0fea14165bb409a099705beb1a1dc63b4e4;p=userspace-rcu.git 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 --- diff --git a/urcu.c b/urcu.c index a26d38f..624d7fc 100644 --- a/urcu.c +++ b/urcu.c @@ -64,18 +64,10 @@ #define RCU_QS_ACTIVE_ATTEMPTS 100 /* - * RCU_MEMBARRIER is only possibly available on Linux. + * The ABI of sys_membarrier changed after its original implementation. + * Disable it for now. Use RCU_MB flavor instead. */ -#if defined(RCU_MEMBARRIER) && defined(__linux__) -#include -#endif - -/* If the headers do not support SYS_membarrier, fall back on RCU_MB */ -#ifdef SYS_membarrier -# define membarrier(...) syscall(SYS_membarrier, __VA_ARGS__) -#else -# define membarrier(...) -ENOSYS -#endif +#define membarrier(...) -ENOSYS #define MEMBARRIER_EXPEDITED (1 << 0) #define MEMBARRIER_DELAYED (1 << 1)