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authorHeiko Carstens <heiko.carstens@de.ibm.com>2014-03-02 13:09:47 +0100
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-04-14 06:42:19 -0700
commitf26c70a452dc0507bf7d3d2c3158ee7808e14f1c (patch)
tree7626bda5305bd7c9013d48ef50d030ade70b4b70
parent47c4534a109e45700d1d1c8467c2b5a618212d81 (diff)
downloadlinux-linaro-stable-f26c70a452dc0507bf7d3d2c3158ee7808e14f1c.tar.gz
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/Kconfig1
-rw-r--r--include/linux/futex.h4
-rw-r--r--init/Kconfig7
-rw-r--r--kernel/futex.c14
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);