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Date: Mon, 3 Mar 2014 02:34:19 -0800
From: tip-bot for Heiko Carstens <tipbot@...or.com>
To: linux-tip-commits@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, hpa@...or.com, mingo@...nel.org,
geert@...ux-m68k.org, fthain@...egraphics.com.au,
heiko.carstens@...ibm.com, tglx@...utronix.de
Subject: [tip:core/locking] futex:
Allow architectures to skip futex_atomic_cmpxchg_inatomic() test
Commit-ID: 03b8c7b623c80af264c4c8d6111e5c6289933666
Gitweb: http://git.kernel.org/tip/03b8c7b623c80af264c4c8d6111e5c6289933666
Author: Heiko Carstens <heiko.carstens@...ibm.com>
AuthorDate: Sun, 2 Mar 2014 13:09:47 +0100
Committer: Thomas Gleixner <tglx@...utronix.de>
CommitDate: Mon, 3 Mar 2014 11:32:08 +0100
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 <heiko.carstens@...ibm.com>
Cc: Finn Thain <fthain@...egraphics.com.au>
Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
Link: http://lkml.kernel.org/r/20140302120947.GA3641@osiris
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
---
arch/s390/Kconfig | 1 +
include/linux/futex.h | 4 ++++
init/Kconfig | 7 +++++++
kernel/futex.c | 37 ++++++++++++++++++++++++-------------
4 files changed, 36 insertions(+), 13 deletions(-)
diff --git a/arch/s390/Kconfig b/arch/s390/Kconfig
index 65a0775..bb74b21 100644
--- a/arch/s390/Kconfig
+++ b/arch/s390/Kconfig
@@ -117,6 +117,7 @@ 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_LZ4
diff --git a/include/linux/futex.h b/include/linux/futex.h
index b0d95ca..6435f46 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 009a797..d56cb03 100644
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1387,6 +1387,13 @@ 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 44a1261..5d17e3a 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);
--
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