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| author | Heiko Carstens <heiko.carstens@de.ibm.com> | 2014-03-02 13:09:47 +0100 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2014-04-14 06:42:19 -0700 |
| commit | f26c70a452dc0507bf7d3d2c3158ee7808e14f1c (patch) | |
| tree | 7626bda5305bd7c9013d48ef50d030ade70b4b70 | |
| parent | 47c4534a109e45700d1d1c8467c2b5a618212d81 (diff) | |
| download | lwn-f26c70a452dc0507bf7d3d2c3158ee7808e14f1c.tar.gz lwn-f26c70a452dc0507bf7d3d2c3158ee7808e14f1c.zip | |
futex: Allow architectures to skip futex_atomic_cmpxchg_inatomic() test
commit 03b8c7b623c80af264c4c8d6111e5c6289933666 upstream.
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 <heiko.carstens@de.ibm.com>
Cc: Finn Thain <fthain@telegraphics.com.au>
Cc: Geert Uytterhoeven <geert@linux-m68k.org>
Link: http://lkml.kernel.org/r/20140302120947.GA3641@osiris
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
[geert: Backported to v3.10..v3.13]
Signed-off-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
| -rw-r--r-- | arch/s390/Kconfig | 1 | ||||
| -rw-r--r-- | include/linux/futex.h | 4 | ||||
| -rw-r--r-- | init/Kconfig | 7 | ||||
| -rw-r--r-- | kernel/futex.c | 14 |
4 files changed, 24 insertions, 2 deletions
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig index 97dcbea97a1c..d8d6eeca56b0 100644 --- a/arch/s390/Kconfig +++ b/arch/s390/Kconfig @@ -116,6 +116,7 @@ config S390 select HAVE_FUNCTION_GRAPH_TRACER select HAVE_FUNCTION_TRACER select HAVE_FUNCTION_TRACE_MCOUNT_TEST + select HAVE_FUTEX_CMPXCHG if FUTEX select HAVE_KERNEL_BZIP2 select HAVE_KERNEL_GZIP select HAVE_KERNEL_LZMA diff --git a/include/linux/futex.h b/include/linux/futex.h index b0d95cac826e..6435f46d6e13 100644 --- a/include/linux/futex.h +++ b/include/linux/futex.h @@ -55,7 +55,11 @@ union futex_key { #ifdef CONFIG_FUTEX extern void exit_robust_list(struct task_struct *curr); extern void exit_pi_state_list(struct task_struct *curr); +#ifdef CONFIG_HAVE_FUTEX_CMPXCHG +#define futex_cmpxchg_enabled 1 +#else extern int futex_cmpxchg_enabled; +#endif #else static inline void exit_robust_list(struct task_struct *curr) { diff --git a/init/Kconfig b/init/Kconfig index 2d9b83104dcf..5d6febaea56d 100644 --- a/init/Kconfig +++ b/init/Kconfig @@ -1365,6 +1365,13 @@ config FUTEX support for "fast userspace mutexes". The resulting kernel may not run glibc-based applications correctly. +config HAVE_FUTEX_CMPXCHG + bool + help + Architectures should select this if futex_atomic_cmpxchg_inatomic() + is implemented and always working. This removes a couple of runtime + checks. + config EPOLL bool "Enable eventpoll support" if EXPERT default y diff --git a/kernel/futex.c b/kernel/futex.c index a283b3041072..3bc18bf48d0c 100644 --- a/kernel/futex.c +++ b/kernel/futex.c @@ -67,7 +67,9 @@ #include "rtmutex_common.h" +#ifndef CONFIG_HAVE_FUTEX_CMPXCHG int __read_mostly futex_cmpxchg_enabled; +#endif #define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8) @@ -2729,10 +2731,10 @@ 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; - int i; /* * This will fail and we want it. Some arch implementations do @@ -2746,6 +2748,14 @@ static int __init futex_init(void) */ if (cmpxchg_futex_value_locked(&curval, NULL, 0, 0) == -EFAULT) futex_cmpxchg_enabled = 1; +#endif +} + +static int __init futex_init(void) +{ + int i; + + futex_detect_cmpxchg(); for (i = 0; i < ARRAY_SIZE(futex_queues); i++) { plist_head_init(&futex_queues[i].chain); |