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futex: Allow architectures to skip futex_atomic_cmpxchg_inatomic() test

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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>
This commit is contained in:
Heiko Carstens 2014-03-02 13:09:47 +01:00 • committed by Thomas Gleixner
parent d2ae2e525e
commit 03b8c7b623
4 changed files with 36 additions and 13 deletions
Download patch file Download diff file Expand all files Collapse all files

37
kernel/futex.c
View file

@ -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 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)
{
u32 curval;
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);