This is a note to let you know that I've just added the patch titled
futex: Allow architectures to skip futex_atomic_cmpxchg_inatomic() test
to the 3.13-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
futex-allow-architectures-to-skip-futex_atomic_cmpxchg_inatomic-test.patch
and it can be found in the queue-3.13 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
>From 03b8c7b623c80af264c4c8d6111e5c6289933666 Mon Sep 17 00:00:00 2001
From: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
Date: Sun, 2 Mar 2014 13:09:47 +0100
Subject: futex: Allow architectures to skip futex_atomic_cmpxchg_inatomic() test
From: Heiko Carstens <heiko.carstens@xxxxxxxxxx>
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@xxxxxxxxxx>
Cc: Finn Thain <fthain@xxxxxxxxxxxxxxxxxxx>
Cc: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
Link: http://lkml.kernel.org/r/20140302120947.GA3641@osiris
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
[geert: Backported to v3.10..v3.13]
Signed-off-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
arch/s390/Kconfig | 1 +
include/linux/futex.h | 4 ++++
init/Kconfig | 7 +++++++
kernel/futex.c | 14 ++++++++++++--
4 files changed, 24 insertions(+), 2 deletions(-)
--- 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
--- 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)
{
--- a/init/Kconfig
+++ b/init/Kconfig
@@ -1399,6 +1399,13 @@ 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
--- a/kernel/futex.c
+++ b/kernel/futex.c
@@ -68,7 +68,9 @@
#include "locking/rtmutex_common.h"
+#ifndef CONFIG_HAVE_FUTEX_CMPXCHG
int __read_mostly futex_cmpxchg_enabled;
+#endif
#define FUTEX_HASHBITS (CONFIG_BASE_SMALL ? 4 : 8)
@@ -2731,10 +2733,10 @@ SYSCALL_DEFINE6(futex, u32 __user *, uad
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
@@ -2748,6 +2750,14 @@ 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);
Patches currently in stable-queue which might be from heiko.carstens@xxxxxxxxxx are
queue-3.13/futex-allow-architectures-to-skip-futex_atomic_cmpxchg_inatomic-test.patch
--
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