Commit 03b8c7b6 authored by Heiko Carstens's avatar Heiko Carstens Committed by Thomas Gleixner
Browse files

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: default avatarHeiko 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: default avatarThomas Gleixner <tglx@linutronix.de>
parent d2ae2e52

arch/s390/Kconfig

+1 −0
Original line number Diff line number Diff line
@@ -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

include/linux/futex.h

+4 −0
Original line number Diff line number Diff line
@@ -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)

{

init/Kconfig

+7 −0
Original line number Diff line number Diff line
@@ -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

kernel/futex.c

+24 −13
Original line number Diff line number Diff line
@@ -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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