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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>
This commit is contained in:
Heiko Carstens 2014-03-02 13:09:47 +01:00 committed by Greg Kroah-Hartman
parent 47c4534a10
commit f26c70a452
4 changed files with 24 additions and 2 deletions
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1
arch/s390/Kconfig
View File

@ -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

4
include/linux/futex.h
View File

@ -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)
{

7
init/Kconfig
View File

@ -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

14
kernel/futex.c
View File

@ -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);