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authorHeiko Carstens <heiko.carstens@de.ibm.com>2014-03-02 13:09:47 +0100
committerThomas Gleixner <tglx@linutronix.de>2014-03-03 11:32:08 +0100
commit03b8c7b623c80af264c4c8d6111e5c6289933666 (patch)
tree7fa99fe8a333d567987e563dfa4ff1cf6ee03f04 /kernel/futex.c
parentMerge branch 'core/urgent' into core/locking (diff)
downloadlinux-03b8c7b623c80af264c4c8d6111e5c6289933666.tar.xz
linux-03b8c7b623c80af264c4c8d6111e5c6289933666.zip
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@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>
Diffstat (limited to 'kernel/futex.c')
-rw-r--r--kernel/futex.c37
1 files changed, 24 insertions, 13 deletions
diff --git a/kernel/futex.c b/kernel/futex.c
index 44a1261cb9ff..5d17e3a83f8c 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);