From 03b8c7b623c80af264c4c8d6111e5c6289933666 Mon Sep 17 00:00:00 2001 From: Heiko Carstens Date: Sun, 2 Mar 2014 13:09:47 +0100 Subject: futex: Allow architectures to skip futex_atomic_cmpxchg_inatomic() test If an architecture has futex_atomic_cmpxchg_inatomic() implemented and there is no runtime check necessary, allow to skip the test within futex_init(). This allows to get rid of some code which would always give the same result, and also allows the compiler to optimize a couple of if statements away. Signed-off-by: Heiko Carstens Cc: Finn Thain Cc: Geert Uytterhoeven Link: http://lkml.kernel.org/r/20140302120947.GA3641@osiris Signed-off-by: Thomas Gleixner --- kernel/futex.c | 37 ++++++++++++++++++++++++------------- 1 file changed, 24 insertions(+), 13 deletions(-) (limited to 'kernel/futex.c') diff --git a/kernel/futex.c b/kernel/futex.c index 44a1261cb9f..5d17e3a83f8 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -157,7 +157,9 @@ * enqueue. */ +#ifndef CONFIG_HAVE_FUTEX_CMPXCHG int __read_mostly futex_cmpxchg_enabled; +#endif /* * Futex flags used to encode options to functions and preserve them across @@ -2843,9 +2845,28 @@ SYSCALL_DEFINE6(futex, u32 __user *, uaddr, int, op, u32, val, return do_futex(uaddr, op, val, tp, uaddr2, val2, val3); } -static int __init futex_init(void) +static void __init futex_detect_cmpxchg(void) { +#ifndef CONFIG_HAVE_FUTEX_CMPXCHG u32 curval; + + /* + * This will fail and we want it. Some arch implementations do + * runtime detection of the futex_atomic_cmpxchg_inatomic() + * functionality. We want to know that before we call in any + * of the complex code paths. Also we want to prevent + * registration of robust lists in that case. NULL is + * guaranteed to fault and we get -EFAULT on functional + * implementation, the non-functional ones will return + * -ENOSYS. + */ + if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT) + futex_cmpxchg_enabled = 1; +#endif +} + +static int __init futex_init(void) +{ unsigned int futex_shift; unsigned long i; @@ -2861,18 +2882,8 @@ static int __init futex_init(void) &futex_shift, NULL, futex_hashsize, futex_hashsize); futex_hashsize = 1UL << futex_shift; - /* - * This will fail and we want it. Some arch implementations do - * runtime detection of the futex_atomic_cmpxchg_inatomic() - * functionality. We want to know that before we call in any - * of the complex code paths. Also we want to prevent - * registration of robust lists in that case. NULL is - * guaranteed to fault and we get -EFAULT on functional - * implementation, the non-functional ones will return - * -ENOSYS. - */ - if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT) - futex_cmpxchg_enabled = 1; + + futex_detect_cmpxchg(); for (i = 0; i < futex_hashsize; i++) { plist_head_init(&futex_queues[i].chain); -- cgit v1.2.3-70-g09d2