[PATCH 4/5] atomic: dec_and_lock use cmpxchg

[Nick Piggin <nickpiggin@yahoo.com.au>]

[-- Attachment #1: Type: text/plain, Size: 368 bytes --]

I noticed David posted a patch to do something similar the
other day. With a generic atomic_cmpxchg available, such a
patch is no longer objectionable to those architectures
that don't #define __HAVE_ARCH_CMPXCHG

Do we want this David? Any other architecture have a super
optimised atomic_dec_and_lock that surpasses this
implementation?

-- 
SUSE Labs, Novell Inc.


[-- Attachment #2: atomic-dec_and_lock-use-cmpxchg.patch --]
[-- Type: text/plain, Size: 22888 bytes --]

Index: linux-2.6/lib/dec_and_lock.c
===================================================================
--- linux-2.6.orig/lib/dec_and_lock.c
+++ linux-2.6/lib/dec_and_lock.c
@@ -3,10 +3,21 @@
 #include <asm/atomic.h>
 
 /*
- * This is an architecture-neutral, but slow,
- * implementation of the notion of "decrement
- * a reference count, and return locked if it
- * decremented to zero".
+ * Decrement v if it is not equal to one, and return non zero.
+ * Otherwise return zero.
+ */
+static int atomic_dec_not_one(atomic_t *v)
+{
+	int c, old;
+	c = atomic_read(v);
+	while (c > 1 && (old = atomic_cmpxchg((v), c, c - 1)) != c)
+		c = old;
+	return c > 1;
+}
+
+/*
+ * Implement an atomic "decrement a reference count, and
+ * return locked if it decremented to zero" operation.
  *
  * NOTE NOTE NOTE! This is _not_ equivalent to
  *
@@ -19,14 +30,16 @@
  * because the spin-lock and the decrement must be
  * "atomic".
  *
- * This slow version gets the spinlock unconditionally,
- * and releases it if it isn't needed. Architectures
- * are encouraged to come up with better approaches,
- * this is trivially done efficiently using a load-locked
- * store-conditional approach, for example.
+ * This version shortcuts the unconditional spin lock on
+ * CONFIG_SMP builds to avoid the expensive lock operation.
  */
 int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
 {
+#ifdef CONFIG_SMP
+	if (atomic_dec_not_one(atomic))
+		return 0;
+#endif
+
 	spin_lock(lock);
 	if (atomic_dec_and_test(atomic))
 		return 1;
Index: linux-2.6/arch/alpha/lib/dec_and_lock.c
===================================================================
--- linux-2.6.orig/arch/alpha/lib/dec_and_lock.c
+++ /dev/null
@@ -1,42 +0,0 @@
-/*
- * arch/alpha/lib/dec_and_lock.c
- *
- * ll/sc version of atomic_dec_and_lock()
- * 
- */
-
-#include <linux/spinlock.h>
-#include <asm/atomic.h>
-
-  asm (".text					\n\
-	.global _atomic_dec_and_lock		\n\
-	.ent _atomic_dec_and_lock		\n\
-	.align	4				\n\
-_atomic_dec_and_lock:				\n\
-	.prologue 0				\n\
-1:	ldl_l	$1, 0($16)			\n\
-	subl	$1, 1, $1			\n\
-	beq	$1, 2f				\n\
-	stl_c	$1, 0($16)			\n\
-	beq	$1, 4f				\n\
-	mb					\n\
-	clr	$0				\n\
-	ret					\n\
-2:	br	$29, 3f				\n\
-3:	ldgp	$29, 0($29)			\n\
-	br	$atomic_dec_and_lock_1..ng	\n\
-	.subsection 2				\n\
-4:	br	1b				\n\
-	.previous				\n\
-	.end _atomic_dec_and_lock");
-
-static int __attribute_used__
-atomic_dec_and_lock_1(atomic_t *atomic, spinlock_t *lock)
-{
-	/* Slow path */
-	spin_lock(lock);
-	if (atomic_dec_and_test(atomic))
-		return 1;
-	spin_unlock(lock);
-	return 0;
-}
Index: linux-2.6/arch/i386/lib/dec_and_lock.c
===================================================================
--- linux-2.6.orig/arch/i386/lib/dec_and_lock.c
+++ /dev/null
@@ -1,42 +0,0 @@
-/*
- * x86 version of "atomic_dec_and_lock()" using
- * the atomic "cmpxchg" instruction.
- *
- * (For CPU's lacking cmpxchg, we use the slow
- * generic version, and this one never even gets
- * compiled).
- */
-
-#include <linux/spinlock.h>
-#include <linux/module.h>
-#include <asm/atomic.h>
-
-int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
-{
-	int counter;
-	int newcount;
-
-repeat:
-	counter = atomic_read(atomic);
-	newcount = counter-1;
-
-	if (!newcount)
-		goto slow_path;
-
-	asm volatile("lock; cmpxchgl %1,%2"
-		:"=a" (newcount)
-		:"r" (newcount), "m" (atomic->counter), "0" (counter));
-
-	/* If the above failed, "eax" will have changed */
-	if (newcount != counter)
-		goto repeat;
-	return 0;
-
-slow_path:
-	spin_lock(lock);
-	if (atomic_dec_and_test(atomic))
-		return 1;
-	spin_unlock(lock);
-	return 0;
-}
-EXPORT_SYMBOL(_atomic_dec_and_lock);
Index: linux-2.6/arch/ia64/lib/dec_and_lock.c
===================================================================
--- linux-2.6.orig/arch/ia64/lib/dec_and_lock.c
+++ /dev/null
@@ -1,42 +0,0 @@
-/*
- * Copyright (C) 2003 Jerome Marchand, Bull S.A.
- *	Cleaned up by David Mosberger-Tang <davidm@hpl.hp.com>
- *
- * This file is released under the GPLv2, or at your option any later version.
- *
- * ia64 version of "atomic_dec_and_lock()" using the atomic "cmpxchg" instruction.  This
- * code is an adaptation of the x86 version of "atomic_dec_and_lock()".
- */
-
-#include <linux/compiler.h>
-#include <linux/module.h>
-#include <linux/spinlock.h>
-#include <asm/atomic.h>
-
-/*
- * Decrement REFCOUNT and if the count reaches zero, acquire the spinlock.  Both of these
- * operations have to be done atomically, so that the count doesn't drop to zero without
- * acquiring the spinlock first.
- */
-int
-_atomic_dec_and_lock (atomic_t *refcount, spinlock_t *lock)
-{
-	int old, new;
-
-	do {
-		old = atomic_read(refcount);
-		new = old - 1;
-
-		if (unlikely (old == 1)) {
-			/* oops, we may be decrementing to zero, do it the slow way... */
-			spin_lock(lock);
-			if (atomic_dec_and_test(refcount))
-				return 1;
-			spin_unlock(lock);
-			return 0;
-		}
-	} while (cmpxchg(&refcount->counter, old, new) != old);
-	return 0;
-}
-
-EXPORT_SYMBOL(_atomic_dec_and_lock);
Index: linux-2.6/arch/mips/lib/dec_and_lock.c
===================================================================
--- linux-2.6.orig/arch/mips/lib/dec_and_lock.c
+++ /dev/null
@@ -1,47 +0,0 @@
-/*
- * MIPS version of atomic_dec_and_lock() using cmpxchg
- *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public License
- * as published by the Free Software Foundation; either version
- * 2 of the License, or (at your option) any later version.
- */
-
-#include <linux/module.h>
-#include <linux/spinlock.h>
-#include <asm/atomic.h>
-#include <asm/system.h>
-
-/*
- * This is an implementation of the notion of "decrement a
- * reference count, and return locked if it decremented to zero".
- *
- * This implementation can be used on any architecture that
- * has a cmpxchg, and where atomic->value is an int holding
- * the value of the atomic (i.e. the high bits aren't used
- * for a lock or anything like that).
- */
-int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
-{
-	int counter;
-	int newcount;
-
-	for (;;) {
-		counter = atomic_read(atomic);
-		newcount = counter - 1;
-		if (!newcount)
-			break;		/* do it the slow way */
-
-		newcount = cmpxchg(&atomic->counter, counter, newcount);
-		if (newcount == counter)
-			return 0;
-	}
-
-	spin_lock(lock);
-	if (atomic_dec_and_test(atomic))
-		return 1;
-	spin_unlock(lock);
-	return 0;
-}
-
-EXPORT_SYMBOL(_atomic_dec_and_lock);
Index: linux-2.6/arch/ppc/lib/dec_and_lock.c
===================================================================
--- linux-2.6.orig/arch/ppc/lib/dec_and_lock.c
+++ /dev/null
@@ -1,38 +0,0 @@
-#include <linux/module.h>
-#include <linux/spinlock.h>
-#include <asm/atomic.h>
-#include <asm/system.h>
-
-/*
- * This is an implementation of the notion of "decrement a
- * reference count, and return locked if it decremented to zero".
- *
- * This implementation can be used on any architecture that
- * has a cmpxchg, and where atomic->value is an int holding
- * the value of the atomic (i.e. the high bits aren't used
- * for a lock or anything like that).
- */
-int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
-{
-	int counter;
-	int newcount;
-
-	for (;;) {
-		counter = atomic_read(atomic);
-		newcount = counter - 1;
-		if (!newcount)
-			break;		/* do it the slow way */
-
-		newcount = cmpxchg(&atomic->counter, counter, newcount);
-		if (newcount == counter)
-			return 0;
-	}
-
-	spin_lock(lock);
-	if (atomic_dec_and_test(atomic))
-		return 1;
-	spin_unlock(lock);
-	return 0;
-}
-
-EXPORT_SYMBOL(_atomic_dec_and_lock);
Index: linux-2.6/arch/ppc64/lib/dec_and_lock.c
===================================================================
--- linux-2.6.orig/arch/ppc64/lib/dec_and_lock.c
+++ /dev/null
@@ -1,47 +0,0 @@
-/*
- * ppc64 version of atomic_dec_and_lock() using cmpxchg
- *
- * This program is free software; you can redistribute it and/or
- * modify it under the terms of the GNU General Public License
- * as published by the Free Software Foundation; either version
- * 2 of the License, or (at your option) any later version.
- */
-
-#include <linux/module.h>
-#include <linux/spinlock.h>
-#include <asm/atomic.h>
-#include <asm/system.h>
-
-/*
- * This is an implementation of the notion of "decrement a
- * reference count, and return locked if it decremented to zero".
- *
- * This implementation can be used on any architecture that
- * has a cmpxchg, and where atomic->value is an int holding
- * the value of the atomic (i.e. the high bits aren't used
- * for a lock or anything like that).
- */
-int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
-{
-	int counter;
-	int newcount;
-
-	for (;;) {
-		counter = atomic_read(atomic);
-		newcount = counter - 1;
-		if (!newcount)
-			break;		/* do it the slow way */
-
-		newcount = cmpxchg(&atomic->counter, counter, newcount);
-		if (newcount == counter)
-			return 0;
-	}
-
-	spin_lock(lock);
-	if (atomic_dec_and_test(atomic))
-		return 1;
-	spin_unlock(lock);
-	return 0;
-}
-
-EXPORT_SYMBOL(_atomic_dec_and_lock);
Index: linux-2.6/arch/x86_64/lib/dec_and_lock.c
===================================================================
--- linux-2.6.orig/arch/x86_64/lib/dec_and_lock.c
+++ /dev/null
@@ -1,40 +0,0 @@
-/*
- * x86 version of "atomic_dec_and_lock()" using
- * the atomic "cmpxchg" instruction.
- *
- * (For CPU's lacking cmpxchg, we use the slow
- * generic version, and this one never even gets
- * compiled).
- */
-
-#include <linux/spinlock.h>
-#include <asm/atomic.h>
-
-int _atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
-{
-	int counter;
-	int newcount;
-
-repeat:
-	counter = atomic_read(atomic);
-	newcount = counter-1;
-
-	if (!newcount)
-		goto slow_path;
-
-	asm volatile("lock; cmpxchgl %1,%2"
-		:"=a" (newcount)
-		:"r" (newcount), "m" (atomic->counter), "0" (counter));
-
-	/* If the above failed, "eax" will have changed */
-	if (newcount != counter)
-		goto repeat;
-	return 0;
-
-slow_path:
-	spin_lock(lock);
-	if (atomic_dec_and_test(atomic))
-		return 1;
-	spin_unlock(lock);
-	return 0;
-}
Index: linux-2.6/lib/Makefile
===================================================================
--- linux-2.6.orig/lib/Makefile
+++ linux-2.6/lib/Makefile
@@ -5,7 +5,7 @@
 lib-y := errno.o ctype.o string.o vsprintf.o cmdline.o \
 	 bust_spinlocks.o rbtree.o radix-tree.o dump_stack.o \
 	 idr.o div64.o int_sqrt.o bitmap.o extable.o prio_tree.o \
-	 sha1.o
+	 sha1.o dec_and_lock.o
 
 lib-y	+= kobject.o kref.o kobject_uevent.o klist.o
 
@@ -24,10 +24,6 @@ lib-$(CONFIG_GENERIC_FIND_NEXT_BIT) += f
 obj-$(CONFIG_LOCK_KERNEL) += kernel_lock.o
 obj-$(CONFIG_DEBUG_PREEMPT) += smp_processor_id.o
 
-ifneq ($(CONFIG_HAVE_DEC_LOCK),y)
-  lib-y += dec_and_lock.o
-endif
-
 obj-$(CONFIG_CRC_CCITT)	+= crc-ccitt.o
 obj-$(CONFIG_CRC16)	+= crc16.o
 obj-$(CONFIG_CRC32)	+= crc32.o
Index: linux-2.6/arch/alpha/Kconfig
===================================================================
--- linux-2.6.orig/arch/alpha/Kconfig
+++ linux-2.6/arch/alpha/Kconfig
@@ -501,11 +501,6 @@ config SMP
 
 	  If you don't know what to do here, say N.
 
-config HAVE_DEC_LOCK
-	bool
-	depends on SMP
-	default y
-
 config NR_CPUS
 	int "Maximum number of CPUs (2-64)"
 	range 2 64
Index: linux-2.6/arch/i386/Kconfig
===================================================================
--- linux-2.6.orig/arch/i386/Kconfig
+++ linux-2.6/arch/i386/Kconfig
@@ -908,11 +908,6 @@ config IRQBALANCE
  	  The default yes will allow the kernel to do irq load balancing.
 	  Saying no will keep the kernel from doing irq load balancing.
 
-config HAVE_DEC_LOCK
-	bool
-	depends on (SMP || PREEMPT) && X86_CMPXCHG
-	default y
-
 # turning this on wastes a bunch of space.
 # Summit needs it only when NUMA is on
 config BOOT_IOREMAP
Index: linux-2.6/arch/i386/lib/Makefile
===================================================================
--- linux-2.6.orig/arch/i386/lib/Makefile
+++ linux-2.6/arch/i386/lib/Makefile
@@ -7,4 +7,3 @@ lib-y = checksum.o delay.o usercopy.o ge
 	bitops.o
 
 lib-$(CONFIG_X86_USE_3DNOW) += mmx.o
-lib-$(CONFIG_HAVE_DEC_LOCK) += dec_and_lock.o
Index: linux-2.6/arch/ia64/Kconfig
===================================================================
--- linux-2.6.orig/arch/ia64/Kconfig
+++ linux-2.6/arch/ia64/Kconfig
@@ -298,11 +298,6 @@ config PREEMPT
 
 source "mm/Kconfig"
 
-config HAVE_DEC_LOCK
-	bool
-	depends on (SMP || PREEMPT)
-	default y
-
 config IA32_SUPPORT
 	bool "Support for Linux/x86 binaries"
 	help
Index: linux-2.6/arch/ia64/lib/Makefile
===================================================================
--- linux-2.6.orig/arch/ia64/lib/Makefile
+++ linux-2.6/arch/ia64/lib/Makefile
@@ -15,7 +15,6 @@ lib-$(CONFIG_ITANIUM)	+= copy_page.o cop
 lib-$(CONFIG_MCKINLEY)	+= copy_page_mck.o memcpy_mck.o
 lib-$(CONFIG_PERFMON)	+= carta_random.o
 lib-$(CONFIG_MD_RAID5)	+= xor.o
-lib-$(CONFIG_HAVE_DEC_LOCK) += dec_and_lock.o
 
 AFLAGS___divdi3.o	=
 AFLAGS___udivdi3.o	= -DUNSIGNED
Index: linux-2.6/arch/m32r/Kconfig
===================================================================
--- linux-2.6.orig/arch/m32r/Kconfig
+++ linux-2.6/arch/m32r/Kconfig
@@ -220,11 +220,6 @@ config PREEMPT
 	  Say Y here if you are building a kernel for a desktop, embedded
 	  or real-time system.  Say N if you are unsure.
 
-config HAVE_DEC_LOCK
-	bool
-	depends on (SMP || PREEMPT)
-	default n
-
 config SMP
 	bool "Symmetric multi-processing support"
 	---help---
Index: linux-2.6/arch/mips/Kconfig
===================================================================
--- linux-2.6.orig/arch/mips/Kconfig
+++ linux-2.6/arch/mips/Kconfig
@@ -1009,10 +1009,6 @@ config GENERIC_CALIBRATE_DELAY
 	bool
 	default y
 
-config HAVE_DEC_LOCK
-	bool
-	default y
-
 #
 # Select some configuration options automatically based on user selections.
 #
Index: linux-2.6/arch/ppc/Kconfig
===================================================================
--- linux-2.6.orig/arch/ppc/Kconfig
+++ linux-2.6/arch/ppc/Kconfig
@@ -26,10 +26,6 @@ config GENERIC_CALIBRATE_DELAY
 	bool
 	default y
 
-config HAVE_DEC_LOCK
-	bool
-	default y
-
 config PPC
 	bool
 	default y
Index: linux-2.6/arch/ppc64/Kconfig
===================================================================
--- linux-2.6.orig/arch/ppc64/Kconfig
+++ linux-2.6/arch/ppc64/Kconfig
@@ -28,10 +28,6 @@ config GENERIC_ISA_DMA
 	bool
 	default y
 
-config HAVE_DEC_LOCK
-	bool
-	default y
-
 config EARLY_PRINTK
 	bool
 	default y
Index: linux-2.6/arch/sparc64/lib/Makefile
===================================================================
--- linux-2.6.orig/arch/sparc64/lib/Makefile
+++ linux-2.6/arch/sparc64/lib/Makefile
@@ -14,6 +14,4 @@ lib-y := PeeCeeI.o copy_page.o clear_pag
 	 copy_in_user.o user_fixup.o memmove.o \
 	 mcount.o ipcsum.o rwsem.o xor.o find_bit.o delay.o
 
-lib-$(CONFIG_HAVE_DEC_LOCK) += dec_and_lock.o
-
 obj-y += iomap.o
Index: linux-2.6/arch/x86_64/Kconfig
===================================================================
--- linux-2.6.orig/arch/x86_64/Kconfig
+++ linux-2.6/arch/x86_64/Kconfig
@@ -277,11 +277,6 @@ source "mm/Kconfig"
 config HAVE_ARCH_EARLY_PFN_TO_NID
 	def_bool y
 
-config HAVE_DEC_LOCK
-	bool
-	depends on SMP
-	default y
-
 config NR_CPUS
 	int "Maximum number of CPUs (2-256)"
 	range 2 256
Index: linux-2.6/arch/x86_64/lib/Makefile
===================================================================
--- linux-2.6.orig/arch/x86_64/lib/Makefile
+++ linux-2.6/arch/x86_64/lib/Makefile
@@ -10,5 +10,3 @@ lib-y := csum-partial.o csum-copy.o csum
 	usercopy.o getuser.o putuser.o  \
 	thunk.o clear_page.o copy_page.o bitstr.o bitops.o
 lib-y += memcpy.o memmove.o memset.o copy_user.o
-
-lib-$(CONFIG_HAVE_DEC_LOCK) += dec_and_lock.o
Index: linux-2.6/arch/xtensa/Kconfig
===================================================================
--- linux-2.6.orig/arch/xtensa/Kconfig
+++ linux-2.6/arch/xtensa/Kconfig
@@ -26,10 +26,6 @@ config RWSEM_XCHGADD_ALGORITHM
 	bool
 	default y
 
-config HAVE_DEC_LOCK
-	bool
-	default y
-
 config GENERIC_HARDIRQS
 	bool
 	default y
Index: linux-2.6/arch/sparc64/lib/dec_and_lock.S
===================================================================
--- linux-2.6.orig/arch/sparc64/lib/dec_and_lock.S
+++ /dev/null
@@ -1,80 +0,0 @@
-/* $Id: dec_and_lock.S,v 1.5 2001/11/18 00:12:56 davem Exp $
- * dec_and_lock.S: Sparc64 version of "atomic_dec_and_lock()"
- *                 using cas and ldstub instructions.
- *
- * Copyright (C) 2000 David S. Miller (davem@redhat.com)
- */
-#include <linux/config.h>
-#include <asm/thread_info.h>
-
-	.text
-	.align	64
-
-	/* CAS basically works like this:
-	 *
-	 * void CAS(MEM, REG1, REG2)
-	 * {
-	 *   START_ATOMIC();
-	 *   if (*(MEM) == REG1) {
-	 *     TMP = *(MEM);
-	 *     *(MEM) = REG2;
-	 *     REG2 = TMP;
-	 *   } else
-	 *     REG2 = *(MEM);
-	 *   END_ATOMIC();
-	 * }
-	 */
-
-	.globl	_atomic_dec_and_lock
-_atomic_dec_and_lock:	/* %o0 = counter, %o1 = lock */
-loop1:	lduw	[%o0], %g2
-	subcc	%g2, 1, %g7
-	be,pn	%icc, start_to_zero
-	 nop
-nzero:	cas	[%o0], %g2, %g7
-	cmp	%g2, %g7
-	bne,pn	%icc, loop1
-	 mov	0, %g1
-
-out:
-	membar	#StoreLoad | #StoreStore
-	retl
-	 mov	%g1, %o0
-start_to_zero:
-#ifdef CONFIG_PREEMPT
-	ldsw	[%g6 + TI_PRE_COUNT], %g3
-	add	%g3, 1, %g3
-	stw	%g3, [%g6 + TI_PRE_COUNT]
-#endif
-to_zero:
-	ldstub	[%o1], %g3
-	membar	#StoreLoad | #StoreStore
-	brnz,pn	%g3, spin_on_lock
-	 nop
-loop2:	cas	[%o0], %g2, %g7		/* ASSERT(g7 == 0) */
-	cmp	%g2, %g7
-
-	be,pt	%icc, out
-	 mov	1, %g1
-	lduw	[%o0], %g2
-	subcc	%g2, 1, %g7
-	be,pn	%icc, loop2
-	 nop
-	membar	#StoreStore | #LoadStore
-	stb	%g0, [%o1]
-#ifdef CONFIG_PREEMPT
-	ldsw	[%g6 + TI_PRE_COUNT], %g3
-	sub	%g3, 1, %g3
-	stw	%g3, [%g6 + TI_PRE_COUNT]
-#endif
-
-	b,pt	%xcc, nzero
-	 nop
-spin_on_lock:
-	ldub	[%o1], %g3
-	membar	#LoadLoad
-	brnz,pt	%g3, spin_on_lock
-	 nop
-	ba,pt	%xcc, to_zero
-	 nop
-	nop
Index: linux-2.6/arch/alpha/kernel/alpha_ksyms.c
===================================================================
--- linux-2.6.orig/arch/alpha/kernel/alpha_ksyms.c
+++ linux-2.6/arch/alpha/kernel/alpha_ksyms.c
@@ -184,7 +184,6 @@ EXPORT_SYMBOL(cpu_data);
 EXPORT_SYMBOL(smp_num_cpus);
 EXPORT_SYMBOL(smp_call_function);
 EXPORT_SYMBOL(smp_call_function_on_cpu);
-EXPORT_SYMBOL(_atomic_dec_and_lock);
 EXPORT_SYMBOL(cpu_present_mask);
 #endif /* CONFIG_SMP */
 
Index: linux-2.6/arch/sparc64/kernel/sparc64_ksyms.c
===================================================================
--- linux-2.6.orig/arch/sparc64/kernel/sparc64_ksyms.c
+++ linux-2.6/arch/sparc64/kernel/sparc64_ksyms.c
@@ -163,9 +163,6 @@ EXPORT_SYMBOL(atomic64_add);
 EXPORT_SYMBOL(atomic64_add_ret);
 EXPORT_SYMBOL(atomic64_sub);
 EXPORT_SYMBOL(atomic64_sub_ret);
-#ifdef CONFIG_SMP
-EXPORT_SYMBOL(_atomic_dec_and_lock);
-#endif
 
 /* Atomic bit operations. */
 EXPORT_SYMBOL(test_and_set_bit);
Index: linux-2.6/arch/x86_64/kernel/x8664_ksyms.c
===================================================================
--- linux-2.6.orig/arch/x86_64/kernel/x8664_ksyms.c
+++ linux-2.6/arch/x86_64/kernel/x8664_ksyms.c
@@ -178,10 +178,6 @@ EXPORT_SYMBOL(rwsem_down_write_failed_th
 
 EXPORT_SYMBOL(empty_zero_page);
 
-#ifdef CONFIG_HAVE_DEC_LOCK
-EXPORT_SYMBOL(_atomic_dec_and_lock);
-#endif
-
 EXPORT_SYMBOL(die_chain);
 EXPORT_SYMBOL(register_die_notifier);
 
Index: linux-2.6/arch/alpha/lib/Makefile
===================================================================
--- linux-2.6.orig/arch/alpha/lib/Makefile
+++ linux-2.6/arch/alpha/lib/Makefile
@@ -40,8 +40,6 @@ lib-y =	__divqu.o __remqu.o __divlu.o __
 	fpreg.o \
 	callback_srm.o srm_puts.o srm_printk.o
 
-lib-$(CONFIG_SMP) += dec_and_lock.o
-
 # The division routines are built from single source, with different defines.
 AFLAGS___divqu.o = -DDIV
 AFLAGS___remqu.o =       -DREM
Index: linux-2.6/arch/mips/lib/Makefile
===================================================================
--- linux-2.6.orig/arch/mips/lib/Makefile
+++ linux-2.6/arch/mips/lib/Makefile
@@ -2,8 +2,7 @@
 # Makefile for MIPS-specific library files..
 #
 
-lib-y	+= csum_partial_copy.o dec_and_lock.o memcpy.o promlib.o \
-	   strlen_user.o strncpy_user.o strnlen_user.o
+lib-y	+= csum_partial_copy.o memcpy.o promlib.o strlen_user.o strncpy_user.o strnlen_user.o
 
 obj-y	+= iomap.o
 
Index: linux-2.6/arch/ppc/lib/Makefile
===================================================================
--- linux-2.6.orig/arch/ppc/lib/Makefile
+++ linux-2.6/arch/ppc/lib/Makefile
@@ -2,7 +2,7 @@
 # Makefile for ppc-specific library files..
 #
 
-obj-y			:= checksum.o string.o strcase.o dec_and_lock.o div64.o
+obj-y			:= checksum.o string.o strcase.o div64.o
 
 obj-$(CONFIG_8xx)	+= rheap.o
 obj-$(CONFIG_CPM2)	+= rheap.o
Index: linux-2.6/arch/ppc64/lib/Makefile
===================================================================
--- linux-2.6.orig/arch/ppc64/lib/Makefile
+++ linux-2.6/arch/ppc64/lib/Makefile
@@ -2,7 +2,7 @@
 # Makefile for ppc64-specific library files..
 #
 
-lib-y := checksum.o dec_and_lock.o string.o strcase.o
+lib-y := checksum.o string.o strcase.o
 lib-y += copypage.o memcpy.o copyuser.o usercopy.o
 
 # Lock primitives are defined as no-ops in include/linux/spinlock.h
Index: linux-2.6/arch/sparc64/Kconfig.debug
===================================================================
--- linux-2.6.orig/arch/sparc64/Kconfig.debug
+++ linux-2.6/arch/sparc64/Kconfig.debug
@@ -33,14 +33,6 @@ config DEBUG_BOOTMEM
 	depends on DEBUG_KERNEL
 	bool "Debug BOOTMEM initialization"
 
-# We have a custom atomic_dec_and_lock() implementation but it's not
-# compatible with spinlock debugging so we need to fall back on
-# the generic version in that case.
-config HAVE_DEC_LOCK
-	bool
-	depends on SMP && !DEBUG_SPINLOCK
-	default y
-
 config MCOUNT
 	bool
 	depends on STACK_DEBUG
Index: linux-2.6/kernel/rcupdate.c
===================================================================
--- linux-2.6.orig/kernel/rcupdate.c
+++ linux-2.6/kernel/rcupdate.c
@@ -45,7 +45,6 @@
 #include <linux/percpu.h>
 #include <linux/notifier.h>
 #include <linux/rcupdate.h>
-#include <linux/rcuref.h>
 #include <linux/cpu.h>
 
 /* Definition for rcupdate control block. */
@@ -73,19 +72,6 @@ DEFINE_PER_CPU(struct rcu_data, rcu_bh_d
 static DEFINE_PER_CPU(struct tasklet_struct, rcu_tasklet) = {NULL};
 static int maxbatch = 10;
 
-#ifndef __HAVE_ARCH_CMPXCHG
-/*
- * We use an array of spinlocks for the rcurefs -- similar to ones in sparc
- * 32 bit atomic_t implementations, and a hash function similar to that
- * for our refcounting needs.
- * Can't help multiprocessors which donot have cmpxchg :(
- */
-
-spinlock_t __rcuref_hash[RCUREF_HASH_SIZE] = {
-	[0 ... (RCUREF_HASH_SIZE-1)] = SPIN_LOCK_UNLOCKED
-};
-#endif
-
 /**
  * call_rcu - Queue an RCU callback for invocation after a grace period.
  * @head: structure to be used for queueing the RCU updates.