From 4dcb7afe15ca3403eabccc73b0a353b253900441 Mon Sep 17 00:00:00 2001 From: Mathieu Desnoyers Date: Fri, 11 Sep 2015 10:33:43 -0400 Subject: [PATCH] Fix: dynamic fallback to compat futex on sys_futex ENOSYS Some MIPS processors (e.g. Cavium Octeon II) dynamically check if the CPU supports ll/sc within sys_futex, and return a ENOSYS errno if they don't, even though the architecture implements sys_futex. Handle this situation by always building the sys_futex compatibility layer, and fall-back on it if sys_futex return a ENOSYS errno. This is a tiny compat layer which adds very little space overhead. This adds an unlikely branch on return from sys_futex, which should not be an issue performance-wise (we've already taken a system call). Since this is a fall-back mode, don't try to be clever, and don't cache the result, so that the common cases (architectures with a properly working sys_futex) don't get two conditional branches, just one. Signed-off-by: Mathieu Desnoyers Acked-by: Paul E. McKenney CC: Michael Jeanson CC: Jon Bernard --- Makefile.am | 2 -- tests/Makefile.am | 2 -- urcu/futex.h | 72 ++++++++++++++++++++++++++++++++++++++--------- 3 files changed, 58 insertions(+), 18 deletions(-) diff --git a/Makefile.am b/Makefile.am index 2396fcf..44cb09b 100644 --- a/Makefile.am +++ b/Makefile.am @@ -37,9 +37,7 @@ else COMPAT= endif -if COMPAT_FUTEX COMPAT+=compat_futex.c -endif RCULFHASH = rculfhash.c rculfhash-mm-order.c rculfhash-mm-chunk.c \ rculfhash-mm-mmap.c diff --git a/tests/Makefile.am b/tests/Makefile.am index 04f6a0c..4daee1b 100644 --- a/tests/Makefile.am +++ b/tests/Makefile.am @@ -25,9 +25,7 @@ else COMPAT= endif -if COMPAT_FUTEX COMPAT+=$(top_srcdir)/compat_futex.c -endif URCU=$(top_srcdir)/urcu.c $(top_srcdir)/urcu-pointer.c $(top_srcdir)/wfqueue.c $(COMPAT) URCU_QSBR=$(top_srcdir)/urcu-qsbr.c $(top_srcdir)/urcu-pointer.c $(top_srcdir)/wfqueue.c $(COMPAT) diff --git a/urcu/futex.h b/urcu/futex.h index b71563b..13d2b1a 100644 --- a/urcu/futex.h +++ b/urcu/futex.h @@ -47,22 +47,66 @@ extern "C" { * (returns EINTR). */ -#ifdef CONFIG_RCU_HAVE_FUTEX -#include -#define futex(...) syscall(__NR_futex, __VA_ARGS__) -#define futex_noasync(uaddr, op, val, timeout, uaddr2, val3) \ - futex(uaddr, op, val, timeout, uaddr2, val3) -#define futex_async(uaddr, op, val, timeout, uaddr2, val3) \ - futex(uaddr, op, val, timeout, uaddr2, val3) -#else extern int compat_futex_noasync(int32_t *uaddr, int op, int32_t val, - const struct timespec *timeout, int32_t *uaddr2, int32_t val3); -#define futex_noasync(uaddr, op, val, timeout, uaddr2, val3) \ - compat_futex_noasync(uaddr, op, val, timeout, uaddr2, val3) + const struct timespec *timeout, int32_t *uaddr2, int32_t val3); extern int compat_futex_async(int32_t *uaddr, int op, int32_t val, - const struct timespec *timeout, int32_t *uaddr2, int32_t val3); -#define futex_async(uaddr, op, val, timeout, uaddr2, val3) \ - compat_futex_async(uaddr, op, val, timeout, uaddr2, val3) + const struct timespec *timeout, int32_t *uaddr2, int32_t val3); + +#ifdef CONFIG_RCU_HAVE_FUTEX + +#include +#include +#include +#include + +static inline int futex(int32_t *uaddr, int op, int32_t val, + const struct timespec *timeout, int32_t *uaddr2, int32_t val3) +{ + return syscall(__NR_futex, uaddr, op, val, timeout, + uaddr2, val3); +} + +static inline int futex_noasync(int32_t *uaddr, int op, int32_t val, + const struct timespec *timeout, int32_t *uaddr2, int32_t val3) +{ + int ret; + + ret = futex(uaddr, op, val, timeout, uaddr2, val3); + if (caa_unlikely(ret < 0 && errno == ENOSYS)) { + return compat_futex_noasync(uaddr, op, val, timeout, + uaddr2, val3); + } + return ret; + +} + +static inline int futex_async(int32_t *uaddr, int op, int32_t val, + const struct timespec *timeout, int32_t *uaddr2, int32_t val3) +{ + int ret; + + ret = futex(uaddr, op, val, timeout, uaddr2, val3); + if (caa_unlikely(ret < 0 && errno == ENOSYS)) { + return compat_futex_async(uaddr, op, val, timeout, + uaddr2, val3); + } + return ret; +} + +#else + +static inline int futex_noasync(int32_t *uaddr, int op, int32_t val, + const struct timespec *timeout, int32_t *uaddr2, int32_t val3) +{ + return compat_futex_noasync(uaddr, op, val, timeout, uaddr2, val3); +} + +static inline int futex_async(int32_t *uaddr, int op, int32_t val, + const struct timespec *timeout, int32_t *uaddr2, int32_t val3) +{ + return compat_futex_async(uaddr, op, val, timeout, uaddr2, val3); +} + #endif #ifdef __cplusplus -- 2.34.1