diff -urN linux-2.4.10/CREDITS linux/CREDITS
--- linux-2.4.10/CREDITS	Sat Oct 20 03:20:24 2001
+++ linux/CREDITS	Sat Oct 20 03:21:15 2001
@@ -965,8 +965,8 @@
 
 N: Nigel Gamble
 E: nigel@nrg.org
-E: nigel@sgi.com
 D: Interrupt-driven printer driver
+D: Preemptible kernel
 S: 120 Alley Way
 S: Mountain View, California 94040
 S: USA
diff -urN linux-2.4.10/Documentation/Configure.help linux/Documentation/Configure.help
--- linux-2.4.10/Documentation/Configure.help	Sat Oct 20 03:20:53 2001
+++ linux/Documentation/Configure.help	Sat Oct 20 03:21:15 2001
@@ -132,6 +132,19 @@
   If you have system with several CPU's, you do not need to say Y
   here: APIC will be used automatically.
 
+Preemptible Kernel
+CONFIG_PREEMPT
+  This option reduces the latency of the kernel when reacting to
+  real-time or interactive events by allowing a low priority process to
+  be preempted even if it is in kernel mode executing a system call.
+  This allows applications to run more reliably even when the system is
+  under load due to other, lower priority, processes.
+
+  Say Y here if you are building a kernel for a desktop system, embedded
+  system or real-time system.  Say N if you are building a kernel for a
+  system where throughput is more important than interactive response,
+  such as a server system.  Say N if you are unsure.
+
 Kernel math emulation
 CONFIG_MATH_EMULATION
   Linux can emulate a math coprocessor (used for floating point
diff -urN linux-2.4.10/MAINTAINERS linux/MAINTAINERS
--- linux-2.4.10/MAINTAINERS	Sat Oct 20 03:20:25 2001
+++ linux/MAINTAINERS	Sat Oct 20 03:21:15 2001
@@ -1151,6 +1151,13 @@
 M:	mostrows@styx.uwaterloo.ca
 S:	Maintained
 
+PREEMPTIBLE KERNEL
+P:	Robert M. Love
+M:	rml@tech9.net
+L:	linux-kernel@vger.kernel.org
+W:	http://tech9.net/rml/linux
+S:	Maintained
+
 PROMISE DC4030 CACHING DISK CONTROLLER DRIVER
 P:	Peter Denison
 M:	promise@pnd-pc.demon.co.uk
diff -urN linux-2.4.10/arch/i386/config.in linux/arch/i386/config.in
--- linux-2.4.10/arch/i386/config.in	Sat Oct 20 03:20:43 2001
+++ linux/arch/i386/config.in	Sat Oct 20 03:21:15 2001
@@ -169,6 +169,7 @@
 bool 'Math emulation' CONFIG_MATH_EMULATION
 bool 'MTRR (Memory Type Range Register) support' CONFIG_MTRR
 bool 'Symmetric multi-processing support' CONFIG_SMP
+bool 'Preemptible Kernel' CONFIG_PREEMPT
 if [ "$CONFIG_SMP" != "y" ]; then
    bool 'APIC and IO-APIC support on uniprocessors' CONFIG_X86_UP_IOAPIC
    if [ "$CONFIG_X86_UP_IOAPIC" = "y" ]; then
@@ -177,8 +178,10 @@
    fi
 fi
 
-if [ "$CONFIG_SMP" = "y" -a "$CONFIG_X86_CMPXCHG" = "y" ]; then
-   define_bool CONFIG_HAVE_DEC_LOCK y
+if [ "$CONFIG_SMP" = "y" -o "$CONFIG_PREEMPT" = "y" ]; then
+   if [ "$CONFIG_X86_CMPXCHG" = "y" ]; then
+      define_bool CONFIG_HAVE_DEC_LOCK y
+   fi
 fi
 endmenu
 
diff -urN linux-2.4.10/arch/i386/kernel/entry.S linux/arch/i386/kernel/entry.S
--- linux-2.4.10/arch/i386/kernel/entry.S	Sat Oct 20 03:20:43 2001
+++ linux/arch/i386/kernel/entry.S	Sat Oct 20 03:21:15 2001
@@ -72,7 +72,7 @@
  * these are offsets into the task-struct.
  */
 state		=  0
-flags		=  4
+preempt_count	=  4
 sigpending	=  8
 addr_limit	= 12
 exec_domain	= 16
@@ -80,8 +80,28 @@
 tsk_ptrace	= 24
 processor	= 52
 
+        /* These are offsets into the irq_stat structure
+         * There is one per cpu and it is aligned to 32
+         * byte boundry (we put that here as a shift count)
+         */
+irq_array_shift                 = CONFIG_X86_L1_CACHE_SHIFT
+
+irq_stat_local_irq_count        = 4
+irq_stat_local_bh_count         = 8
+
 ENOSYS = 38
 
+#ifdef CONFIG_SMP
+#define GET_CPU_INDX	movl processor(%ebx),%eax;  \
+                        shll $irq_array_shift,%eax
+#define GET_CURRENT_CPU_INDX GET_CURRENT(%ebx); \
+                             GET_CPU_INDX
+#define CPU_INDX (,%eax)
+#else
+#define GET_CPU_INDX
+#define GET_CURRENT_CPU_INDX GET_CURRENT(%ebx)
+#define CPU_INDX
+#endif
 
 #define SAVE_ALL \
 	cld; \
@@ -248,12 +268,30 @@
 	ALIGN
 ENTRY(ret_from_intr)
 	GET_CURRENT(%ebx)
+#ifdef CONFIG_PREEMPT
+	cli
+	decl preempt_count(%ebx)
+#endif
 ret_from_exception:
 	movl EFLAGS(%esp),%eax		# mix EFLAGS and CS
 	movb CS(%esp),%al
 	testl $(VM_MASK | 3),%eax	# return to VM86 mode or non-supervisor?
 	jne ret_from_sys_call
+#ifdef CONFIG_PREEMPT
+	cmpl $0,preempt_count(%ebx)
+	jnz restore_all
+	cmpl $0,need_resched(%ebx)
+	jz restore_all
+	movl SYMBOL_NAME(irq_stat)+irq_stat_local_bh_count CPU_INDX,%ecx
+	addl SYMBOL_NAME(irq_stat)+irq_stat_local_irq_count CPU_INDX,%ecx
+	jnz restore_all
+	incl preempt_count(%ebx)
+	sti
+	call SYMBOL_NAME(preempt_schedule)
+	jmp ret_from_intr
+#else
 	jmp restore_all
+#endif
 
 	ALIGN
 reschedule:
@@ -290,6 +328,9 @@
 	GET_CURRENT(%ebx)
 	call *%edi
 	addl $8,%esp
+#ifdef CONFIG_PREEMPT
+	cli
+#endif
 	jmp ret_from_exception
 
 ENTRY(coprocessor_error)
@@ -309,12 +350,18 @@
 	movl %cr0,%eax
 	testl $0x4,%eax			# EM (math emulation bit)
 	jne device_not_available_emulate
+#ifdef CONFIG_PREEMPT
+	cli
+#endif
 	call SYMBOL_NAME(math_state_restore)
 	jmp ret_from_exception
 device_not_available_emulate:
 	pushl $0		# temporary storage for ORIG_EIP
 	call  SYMBOL_NAME(math_emulate)
 	addl $4,%esp
+#ifdef CONFIG_PREEMPT
+	cli
+#endif
 	jmp ret_from_exception
 
 ENTRY(debug)
diff -urN linux-2.4.10/arch/i386/kernel/i387.c linux/arch/i386/kernel/i387.c
--- linux-2.4.10/arch/i386/kernel/i387.c	Sat Oct 20 03:20:43 2001
+++ linux/arch/i386/kernel/i387.c	Sat Oct 20 03:21:15 2001
@@ -10,6 +10,7 @@
 
 #include <linux/config.h>
 #include <linux/sched.h>
+#include <linux/spinlock.h>
 #include <asm/processor.h>
 #include <asm/i387.h>
 #include <asm/math_emu.h>
@@ -65,6 +66,8 @@
 {
 	struct task_struct *tsk = current;
 
+	preempt_disable();
+	
 	if (tsk->flags & PF_USEDFPU) {
 		__save_init_fpu(tsk);
 		return;
diff -urN linux-2.4.10/arch/i386/kernel/traps.c linux/arch/i386/kernel/traps.c
--- linux-2.4.10/arch/i386/kernel/traps.c	Sat Oct 20 03:20:43 2001
+++ linux/arch/i386/kernel/traps.c	Sat Oct 20 03:21:15 2001
@@ -697,6 +697,11 @@
  */
 asmlinkage void math_state_restore(struct pt_regs regs)
 {
+	/*
+	 * CONFIG_PREEMPT
+	 * Must be called with preemption disabled
+	 */
+
 	__asm__ __volatile__("clts");		/* Allow maths ops (or we recurse) */
 
 	if (current->used_math) {
diff -urN linux-2.4.10/arch/i386/lib/dec_and_lock.c linux/arch/i386/lib/dec_and_lock.c
--- linux-2.4.10/arch/i386/lib/dec_and_lock.c	Sat Oct 20 03:20:43 2001
+++ linux/arch/i386/lib/dec_and_lock.c	Sat Oct 20 03:21:15 2001
@@ -8,6 +8,7 @@
  */
 
 #include <linux/spinlock.h>
+#include <linux/sched.h>
 #include <asm/atomic.h>
 
 int atomic_dec_and_lock(atomic_t *atomic, spinlock_t *lock)
diff -urN linux-2.4.10/drivers/ieee1394/csr.c linux/drivers/ieee1394/csr.c
--- linux-2.4.10/drivers/ieee1394/csr.c	Sat Oct 20 03:20:39 2001
+++ linux/drivers/ieee1394/csr.c	Sat Oct 20 03:21:15 2001
@@ -10,6 +10,7 @@
  */
 
 #include <linux/string.h>
+#include <linux/sched.h>
 
 #include "ieee1394_types.h"
 #include "hosts.h"
diff -urN linux-2.4.10/fs/adfs/map.c linux/fs/adfs/map.c
--- linux-2.4.10/fs/adfs/map.c	Sat Oct 20 03:20:24 2001
+++ linux/fs/adfs/map.c	Sat Oct 20 03:21:15 2001
@@ -12,6 +12,7 @@
 #include <linux/fs.h>
 #include <linux/adfs_fs.h>
 #include <linux/spinlock.h>
+#include <linux/sched.h>
 
 #include "adfs.h"
 
diff -urN linux-2.4.10/fs/exec.c linux/fs/exec.c
--- linux-2.4.10/fs/exec.c	Sat Oct 20 03:20:24 2001
+++ linux/fs/exec.c	Sat Oct 20 03:21:15 2001
@@ -419,8 +419,8 @@
 		active_mm = current->active_mm;
 		current->mm = mm;
 		current->active_mm = mm;
-		task_unlock(current);
 		activate_mm(active_mm, mm);
+		task_unlock(current);
 		mm_release();
 		if (old_mm) {
 			if (active_mm != old_mm) BUG();
diff -urN linux-2.4.10/fs/fat/cache.c linux/fs/fat/cache.c
--- linux-2.4.10/fs/fat/cache.c	Sat Oct 20 03:20:24 2001
+++ linux/fs/fat/cache.c	Sat Oct 20 03:21:15 2001
@@ -14,6 +14,7 @@
 #include <linux/string.h>
 #include <linux/stat.h>
 #include <linux/fat_cvf.h>
+#include <linux/sched.h>
 
 #include "msbuffer.h"
 
diff -urN linux-2.4.10/include/asm-i386/hardirq.h linux/include/asm-i386/hardirq.h
--- linux-2.4.10/include/asm-i386/hardirq.h	Sat Oct 20 03:20:24 2001
+++ linux/include/asm-i386/hardirq.h	Sat Oct 20 03:21:15 2001
@@ -36,6 +36,8 @@
 
 #define synchronize_irq()	barrier()
 
+#define release_irqlock(cpu)	do { } while (0)
+
 #else
 
 #include <asm/atomic.h>
diff -urN linux-2.4.10/include/asm-i386/highmem.h linux/include/asm-i386/highmem.h
--- linux-2.4.10/include/asm-i386/highmem.h	Sat Oct 20 03:20:24 2001
+++ linux/include/asm-i386/highmem.h	Sat Oct 20 03:21:15 2001
@@ -85,6 +85,7 @@
 	enum fixed_addresses idx;
 	unsigned long vaddr;
 
+	preempt_disable();
 	if (page < highmem_start_page)
 		return page_address(page);
 
@@ -106,8 +107,10 @@
 	unsigned long vaddr = (unsigned long) kvaddr;
 	enum fixed_addresses idx = type + KM_TYPE_NR*smp_processor_id();
 
-	if (vaddr < FIXADDR_START) // FIXME
+	if (vaddr < FIXADDR_START) { // FIXME
+		preempt_enable();
 		return;
+	}
 
 	if (vaddr != __fix_to_virt(FIX_KMAP_BEGIN+idx))
 		BUG();
@@ -119,6 +122,7 @@
 	pte_clear(kmap_pte-idx);
 	__flush_tlb_one(vaddr);
 #endif
+	preempt_enable();
 }
 
 #endif /* __KERNEL__ */
diff -urN linux-2.4.10/include/asm-i386/hw_irq.h linux/include/asm-i386/hw_irq.h
--- linux-2.4.10/include/asm-i386/hw_irq.h	Sat Oct 20 03:20:24 2001
+++ linux/include/asm-i386/hw_irq.h	Sat Oct 20 03:21:15 2001
@@ -95,6 +95,18 @@
 #define __STR(x) #x
 #define STR(x) __STR(x)
 
+#define GET_CURRENT \
+	"movl %esp, %ebx\n\t" \
+	"andl $-8192, %ebx\n\t"
+
+#ifdef CONFIG_PREEMPT
+#define BUMP_CONTEX_SWITCH_LOCK \
+	GET_CURRENT \
+	"incl 4(%ebx)\n\t"
+#else
+#define BUMP_CONTEX_SWITCH_LOCK
+#endif
+
 #define SAVE_ALL \
 	"cld\n\t" \
 	"pushl %es\n\t" \
@@ -108,15 +120,12 @@
 	"pushl %ebx\n\t" \
 	"movl $" STR(__KERNEL_DS) ",%edx\n\t" \
 	"movl %edx,%ds\n\t" \
-	"movl %edx,%es\n\t"
+	"movl %edx,%es\n\t" \
+	BUMP_CONTEX_SWITCH_LOCK
 
 #define IRQ_NAME2(nr) nr##_interrupt(void)
 #define IRQ_NAME(nr) IRQ_NAME2(IRQ##nr)
 
-#define GET_CURRENT \
-	"movl %esp, %ebx\n\t" \
-	"andl $-8192, %ebx\n\t"
-
 /*
  *	SMP has a few special interrupts for IPI messages
  */
diff -urN linux-2.4.10/include/asm-i386/i387.h linux/include/asm-i386/i387.h
--- linux-2.4.10/include/asm-i386/i387.h	Sat Oct 20 03:20:24 2001
+++ linux/include/asm-i386/i387.h	Sat Oct 20 03:21:15 2001
@@ -12,6 +12,7 @@
 #define __ASM_I386_I387_H
 
 #include <linux/sched.h>
+#include <linux/spinlock.h>
 #include <asm/processor.h>
 #include <asm/sigcontext.h>
 #include <asm/user.h>
@@ -24,7 +25,7 @@
 extern void restore_fpu( struct task_struct *tsk );
 
 extern void kernel_fpu_begin(void);
-#define kernel_fpu_end() stts()
+#define kernel_fpu_end() do { stts(); preempt_enable(); } while(0)
 
 
 #define unlazy_fpu( tsk ) do { \
diff -urN linux-2.4.10/include/asm-i386/mmu_context.h linux/include/asm-i386/mmu_context.h
--- linux-2.4.10/include/asm-i386/mmu_context.h	Sat Oct 20 03:20:24 2001
+++ linux/include/asm-i386/mmu_context.h	Sat Oct 20 03:21:15 2001
@@ -27,6 +27,10 @@
 
 static inline void switch_mm(struct mm_struct *prev, struct mm_struct *next, struct task_struct *tsk, unsigned cpu)
 {
+#ifdef CONFIG_PREEMPT
+	if (preempt_is_disable() == 0)
+		BUG();
+#endif
 	if (prev != next) {
 		/* stop flush ipis for the previous mm */
 		clear_bit(cpu, &prev->cpu_vm_mask);
diff -urN linux-2.4.10/include/asm-i386/pgalloc.h linux/include/asm-i386/pgalloc.h
--- linux-2.4.10/include/asm-i386/pgalloc.h	Sat Oct 20 03:20:24 2001
+++ linux/include/asm-i386/pgalloc.h	Sat Oct 20 03:21:15 2001
@@ -65,20 +65,26 @@
 {
 	unsigned long *ret;
 
+	preempt_disable();
 	if ((ret = pgd_quicklist) != NULL) {
 		pgd_quicklist = (unsigned long *)(*ret);
 		ret[0] = 0;
 		pgtable_cache_size--;
-	} else
+		preempt_enable();
+	} else {
+		preempt_enable();
 		ret = (unsigned long *)get_pgd_slow();
+	}
 	return (pgd_t *)ret;
 }
 
 static __inline__ void free_pgd_fast(pgd_t *pgd)
 {
+	preempt_disable();
 	*(unsigned long *)pgd = (unsigned long) pgd_quicklist;
 	pgd_quicklist = (unsigned long *) pgd;
 	pgtable_cache_size++;
+	preempt_enable();
 }
 
 static __inline__ void free_pgd_slow(pgd_t *pgd)
@@ -108,19 +114,23 @@
 {
 	unsigned long *ret;
 
+	preempt_disable();
 	if ((ret = (unsigned long *)pte_quicklist) != NULL) {
 		pte_quicklist = (unsigned long *)(*ret);
 		ret[0] = ret[1];
 		pgtable_cache_size--;
 	}
+	preempt_enable();
 	return (pte_t *)ret;
 }
 
 static __inline__ void pte_free_fast(pte_t *pte)
 {
+	preempt_disable();
 	*(unsigned long *)pte = (unsigned long) pte_quicklist;
 	pte_quicklist = (unsigned long *) pte;
 	pgtable_cache_size++;
+	preempt_enable();
 }
 
 static __inline__ void pte_free_slow(pte_t *pte)
diff -urN linux-2.4.10/include/asm-i386/processor.h linux/include/asm-i386/processor.h
--- linux-2.4.10/include/asm-i386/processor.h	Sat Oct 20 03:20:24 2001
+++ linux/include/asm-i386/processor.h	Sat Oct 20 03:21:15 2001
@@ -500,7 +500,10 @@
 {
 	 __asm__ __volatile__ ("prefetchw (%0)" : : "r"(x));
 }
-#define spin_lock_prefetch(x)	prefetchw(x)
+#define spin_lock_prefetch(x) do {				\
+	prefetchw(x);						\
+	preempt_prefetch(&current->preempt_count.counter);	\
+} while(0)
 
 #endif
 
diff -urN linux-2.4.10/include/asm-i386/smplock.h linux/include/asm-i386/smplock.h
--- linux-2.4.10/include/asm-i386/smplock.h	Sat Oct 20 03:20:24 2001
+++ linux/include/asm-i386/smplock.h	Sat Oct 20 03:21:15 2001
@@ -10,7 +10,15 @@
 
 extern spinlock_t kernel_flag;
 
+#ifdef CONFIG_SMP
 #define kernel_locked()		spin_is_locked(&kernel_flag)
+#else
+#ifdef CONFIG_PREEMPT
+#define kernel_locked()		preempt_is_disable()
+#else
+#define kernel_locked()		1
+#endif
+#endif
 
 /*
  * Release global kernel lock and global interrupt lock
@@ -42,6 +50,11 @@
  */
 static __inline__ void lock_kernel(void)
 {
+#ifdef CONFIG_PREEMPT
+	if (current->lock_depth == -1)
+		spin_lock(&kernel_flag);
+	++current->lock_depth;
+#else
 #if 1
 	if (!++current->lock_depth)
 		spin_lock(&kernel_flag);
@@ -54,6 +67,7 @@
 		:"=m" (__dummy_lock(&kernel_flag)),
 		 "=m" (current->lock_depth));
 #endif
+#endif
 }
 
 static __inline__ void unlock_kernel(void)
diff -urN linux-2.4.10/include/asm-i386/softirq.h linux/include/asm-i386/softirq.h
--- linux-2.4.10/include/asm-i386/softirq.h	Sat Oct 20 03:20:24 2001
+++ linux/include/asm-i386/softirq.h	Sat Oct 20 03:21:15 2001
@@ -5,9 +5,9 @@
 #include <asm/hardirq.h>
 
 #define __cpu_bh_enable(cpu) \
-		do { barrier(); local_bh_count(cpu)--; } while (0)
+		do { barrier(); local_bh_count(cpu)--; preempt_enable(); } while (0)
 #define cpu_bh_disable(cpu) \
-		do { local_bh_count(cpu)++; barrier(); } while (0)
+		do { preempt_disable(); local_bh_count(cpu)++; barrier(); } while (0)
 
 #define local_bh_disable()	cpu_bh_disable(smp_processor_id())
 #define __local_bh_enable()	__cpu_bh_enable(smp_processor_id())
@@ -22,7 +22,7 @@
  * If you change the offsets in irq_stat then you have to
  * update this code as well.
  */
-#define local_bh_enable()						\
+#define _local_bh_enable()						\
 do {									\
 	unsigned int *ptr = &local_bh_count(smp_processor_id());	\
 									\
@@ -45,4 +45,6 @@
 		/* no registers clobbered */ );				\
 } while (0)
 
+#define local_bh_enable() do { _local_bh_enable(); preempt_enable(); } while (0)
+
 #endif	/* __ASM_SOFTIRQ_H */
diff -urN linux-2.4.10/include/asm-i386/spinlock.h linux/include/asm-i386/spinlock.h
--- linux-2.4.10/include/asm-i386/spinlock.h	Sat Oct 20 03:20:24 2001
+++ linux/include/asm-i386/spinlock.h	Sat Oct 20 03:21:15 2001
@@ -70,7 +70,7 @@
 #define spin_unlock_string \
 	"movb $1,%0"
 
-static inline int spin_trylock(spinlock_t *lock)
+static inline int _raw_spin_trylock(spinlock_t *lock)
 {
 	char oldval;
 	__asm__ __volatile__(
@@ -80,7 +80,7 @@
 	return oldval > 0;
 }
 
-static inline void spin_lock(spinlock_t *lock)
+static inline void _raw_spin_lock(spinlock_t *lock)
 {
 #if SPINLOCK_DEBUG
 	__label__ here;
@@ -95,7 +95,7 @@
 		:"=m" (lock->lock) : : "memory");
 }
 
-static inline void spin_unlock(spinlock_t *lock)
+static inline void _raw_spin_unlock(spinlock_t *lock)
 {
 #if SPINLOCK_DEBUG
 	if (lock->magic != SPINLOCK_MAGIC)
@@ -148,7 +148,7 @@
  */
 /* the spinlock helpers are in arch/i386/kernel/semaphore.c */
 
-static inline void read_lock(rwlock_t *rw)
+static inline void _raw_read_lock(rwlock_t *rw)
 {
 #if SPINLOCK_DEBUG
 	if (rw->magic != RWLOCK_MAGIC)
@@ -157,7 +157,7 @@
 	__build_read_lock(rw, "__read_lock_failed");
 }
 
-static inline void write_lock(rwlock_t *rw)
+static inline void _raw_write_lock(rwlock_t *rw)
 {
 #if SPINLOCK_DEBUG
 	if (rw->magic != RWLOCK_MAGIC)
@@ -166,10 +166,10 @@
 	__build_write_lock(rw, "__write_lock_failed");
 }
 
-#define read_unlock(rw)		asm volatile("lock ; incl %0" :"=m" ((rw)->lock) : : "memory")
-#define write_unlock(rw)	asm volatile("lock ; addl $" RW_LOCK_BIAS_STR ",%0":"=m" ((rw)->lock) : : "memory")
+#define _raw_read_unlock(rw)		asm volatile("lock ; incl %0" :"=m" ((rw)->lock) : : "memory")
+#define _raw_write_unlock(rw)	asm volatile("lock ; addl $" RW_LOCK_BIAS_STR ",%0":"=m" ((rw)->lock) : : "memory")
 
-static inline int write_trylock(rwlock_t *lock)
+static inline int _raw_write_trylock(rwlock_t *lock)
 {
 	atomic_t *count = (atomic_t *)lock;
 	if (atomic_sub_and_test(RW_LOCK_BIAS, count))
diff -urN linux-2.4.10/include/linux/brlock.h linux/include/linux/brlock.h
--- linux-2.4.10/include/linux/brlock.h	Sat Oct 20 03:20:24 2001
+++ linux/include/linux/brlock.h	Sat Oct 20 03:21:15 2001
@@ -171,11 +171,11 @@
 }
 
 #else
-# define br_read_lock(idx)	((void)(idx))
-# define br_read_unlock(idx)	((void)(idx))
-# define br_write_lock(idx)	((void)(idx))
-# define br_write_unlock(idx)	((void)(idx))
-#endif
+# define br_read_lock(idx)	({ (void)(idx); preempt_disable(); })
+# define br_read_unlock(idx)	({ (void)(idx); preempt_enable(); })
+# define br_write_lock(idx)	({ (void)(idx); preempt_disable(); })
+# define br_write_unlock(idx)	({ (void)(idx); preempt_enable(); })
+#endif	/* CONFIG_SMP */
 
 /*
  * Now enumerate all of the possible sw/hw IRQ protected
diff -urN linux-2.4.10/include/linux/dcache.h linux/include/linux/dcache.h
--- linux-2.4.10/include/linux/dcache.h	Sat Oct 20 03:20:24 2001
+++ linux/include/linux/dcache.h	Sat Oct 20 03:21:15 2001
@@ -126,31 +126,6 @@
 
 extern spinlock_t dcache_lock;
 
-/**
- * d_drop - drop a dentry
- * @dentry: dentry to drop
- *
- * d_drop() unhashes the entry from the parent
- * dentry hashes, so that it won't be found through
- * a VFS lookup any more. Note that this is different
- * from deleting the dentry - d_delete will try to
- * mark the dentry negative if possible, giving a
- * successful _negative_ lookup, while d_drop will
- * just make the cache lookup fail.
- *
- * d_drop() is used mainly for stuff that wants
- * to invalidate a dentry for some reason (NFS
- * timeouts or autofs deletes).
- */
-
-static __inline__ void d_drop(struct dentry * dentry)
-{
-	spin_lock(&dcache_lock);
-	list_del(&dentry->d_hash);
-	INIT_LIST_HEAD(&dentry->d_hash);
-	spin_unlock(&dcache_lock);
-}
-
 static __inline__ int dname_external(struct dentry *d)
 {
 	return d->d_name.name != d->d_iname; 
@@ -272,3 +247,34 @@
 #endif /* __KERNEL__ */
 
 #endif	/* __LINUX_DCACHE_H */
+
+#if !defined(__LINUX_DCACHE_H_INLINES) && defined(_TASK_STRUCT_DEFINED)
+#define __LINUX_DCACHE_H_INLINES
+
+#ifdef __KERNEL__
+/**
+ * d_drop - drop a dentry
+ * @dentry: dentry to drop
+ *
+ * d_drop() unhashes the entry from the parent
+ * dentry hashes, so that it won't be found through
+ * a VFS lookup any more. Note that this is different
+ * from deleting the dentry - d_delete will try to
+ * mark the dentry negative if possible, giving a
+ * successful _negative_ lookup, while d_drop will
+ * just make the cache lookup fail.
+ *
+ * d_drop() is used mainly for stuff that wants
+ * to invalidate a dentry for some reason (NFS
+ * timeouts or autofs deletes).
+ */
+
+static __inline__ void d_drop(struct dentry * dentry)
+{
+	spin_lock(&dcache_lock);
+	list_del(&dentry->d_hash);
+	INIT_LIST_HEAD(&dentry->d_hash);
+	spin_unlock(&dcache_lock);
+}
+#endif
+#endif
diff -urN linux-2.4.10/include/linux/fs_struct.h linux/include/linux/fs_struct.h
--- linux-2.4.10/include/linux/fs_struct.h	Sat Oct 20 03:20:24 2001
+++ linux/include/linux/fs_struct.h	Sat Oct 20 03:21:15 2001
@@ -20,6 +20,15 @@
 extern void exit_fs(struct task_struct *);
 extern void set_fs_altroot(void);
 
+struct fs_struct *copy_fs_struct(struct fs_struct *old);
+void put_fs_struct(struct fs_struct *fs);
+
+#endif
+#endif
+
+#if !defined(_LINUX_FS_STRUCT_H_INLINES) && defined(_TASK_STRUCT_DEFINED)
+#define _LINUX_FS_STRUCT_H_INLINES
+#ifdef __KERNEL__
 /*
  * Replace the fs->{rootmnt,root} with {mnt,dentry}. Put the old values.
  * It can block. Requires the big lock held.
@@ -65,9 +74,5 @@
 		mntput(old_pwdmnt);
 	}
 }
-
-struct fs_struct *copy_fs_struct(struct fs_struct *old);
-void put_fs_struct(struct fs_struct *fs);
-
 #endif
 #endif
diff -urN linux-2.4.10/include/linux/sched.h linux/include/linux/sched.h
--- linux-2.4.10/include/linux/sched.h	Sat Oct 20 03:20:24 2001
+++ linux/include/linux/sched.h	Sat Oct 20 03:21:15 2001
@@ -88,6 +88,7 @@
 #define TASK_UNINTERRUPTIBLE	2
 #define TASK_ZOMBIE		4
 #define TASK_STOPPED		8
+#define PREEMPT_ACTIVE		0x40000000
 
 #define __set_task_state(tsk, state_value)		\
 	do { (tsk)->state = (state_value); } while (0)
@@ -154,6 +155,9 @@
 #define	MAX_SCHEDULE_TIMEOUT	LONG_MAX
 extern signed long FASTCALL(schedule_timeout(signed long timeout));
 asmlinkage void schedule(void);
+#ifdef CONFIG_PREEMPT
+asmlinkage void preempt_schedule(void);
+#endif
 
 extern int schedule_task(struct tq_struct *task);
 extern void flush_scheduled_tasks(void);
@@ -283,7 +287,17 @@
 	 * offsets of these are hardcoded elsewhere - touch with care
 	 */
 	volatile long state;	/* -1 unrunnable, 0 runnable, >0 stopped */
+#ifdef CONFIG_PREEMPT
+        /*
+         * We want the preempt_count in this cache line, but we
+         * a) don't want to mess up the offsets in asm code, and
+         * b) the alignment of the next line below,
+         * so we move "flags" down
+         */
+	atomic_t preempt_count;          /* 0=> preemptable, < 0 => BUG */
+#else
 	unsigned long flags;	/* per process flags, defined below */
+#endif
 	int sigpending;
 	mm_segment_t addr_limit;	/* thread address space:
 					 	0-0xBFFFFFFF for user-thead
@@ -317,6 +331,10 @@
 	struct mm_struct *active_mm;
 	struct list_head local_pages;
 	unsigned int allocation_order, nr_local_pages;
+#ifdef CONFIG_PREEMPT
+	unsigned long flags;	/* per process flags, defined below */
+#endif
+
 
 /* task state */
 	struct linux_binfmt *binfmt;
@@ -899,6 +917,11 @@
 	return res;
 }
 
+#define _TASK_STRUCT_DEFINED
+#include <linux/dcache.h>
+#include <linux/tqueue.h>
+#include <linux/fs_struct.h>
+
 #endif /* __KERNEL__ */
 
 #endif
diff -urN linux-2.4.10/include/linux/smp.h linux/include/linux/smp.h
--- linux-2.4.10/include/linux/smp.h	Sat Oct 20 03:20:24 2001
+++ linux/include/linux/smp.h	Sat Oct 20 03:21:15 2001
@@ -81,7 +81,9 @@
 #define smp_processor_id()			0
 #define hard_smp_processor_id()			0
 #define smp_threads_ready			1
+#ifndef CONFIG_PREEMPT
 #define kernel_lock()
+#endif
 #define cpu_logical_map(cpu)			0
 #define cpu_number_map(cpu)			0
 #define smp_call_function(func,info,retry,wait)	({ 0; })
diff -urN linux-2.4.10/include/linux/smp_lock.h linux/include/linux/smp_lock.h
--- linux-2.4.10/include/linux/smp_lock.h	Sat Oct 20 03:20:24 2001
+++ linux/include/linux/smp_lock.h	Sat Oct 20 03:21:15 2001
@@ -3,7 +3,7 @@
 
 #include <linux/config.h>
 
-#ifndef CONFIG_SMP
+#if !defined(CONFIG_SMP) && !defined(CONFIG_PREEMPT)
 
 #define lock_kernel()				do { } while(0)
 #define unlock_kernel()				do { } while(0)
diff -urN linux-2.4.10/include/linux/spinlock.h linux/include/linux/spinlock.h
--- linux-2.4.10/include/linux/spinlock.h	Sat Oct 20 03:20:24 2001
+++ linux/include/linux/spinlock.h	Sat Oct 20 03:21:15 2001
@@ -41,7 +41,9 @@
 
 #if (DEBUG_SPINLOCKS < 1)
 
+#ifndef CONFIG_PREEMPT
 #define atomic_dec_and_lock(atomic,lock) atomic_dec_and_test(atomic)
+#endif
 
 /*
  * Your basic spinlocks, allowing only a single CPU anywhere
@@ -57,11 +59,11 @@
 #endif
 
 #define spin_lock_init(lock)	do { } while(0)
-#define spin_lock(lock)		(void)(lock) /* Not "unused variable". */
+#define _raw_spin_lock(lock)	(void)(lock) /* Not "unused variable". */
 #define spin_is_locked(lock)	(0)
-#define spin_trylock(lock)	({1; })
+#define _raw_spin_trylock(lock)	({1; })
 #define spin_unlock_wait(lock)	do { } while(0)
-#define spin_unlock(lock)	do { } while(0)
+#define _raw_spin_unlock(lock)	do { } while(0)
 
 #elif (DEBUG_SPINLOCKS < 2)
 
@@ -120,12 +122,72 @@
 #endif
 
 #define rwlock_init(lock)	do { } while(0)
-#define read_lock(lock)		(void)(lock) /* Not "unused variable". */
-#define read_unlock(lock)	do { } while(0)
-#define write_lock(lock)	(void)(lock) /* Not "unused variable". */
-#define write_unlock(lock)	do { } while(0)
+#define _raw_read_lock(lock)	(void)(lock) /* Not "unused variable". */
+#define _raw_read_unlock(lock)	do { } while(0)
+#define _raw_write_lock(lock)	(void)(lock) /* Not "unused variable". */
+#define _raw_write_unlock(lock)	do { } while(0)
 
 #endif /* !SMP */
+  
+#ifdef CONFIG_PREEMPT
+
+#define switch_lock_count() current->preempt_count
+#define preempt_is_disable() (switch_lock_count().counter)
+#define atomic_ptr_preempt_count() (&switch_lock_count())
+#define preempt_prefetch(a) prefetchw(a)
+
+#define preempt_disable() do {			\
+	atomic_inc(atomic_ptr_preempt_count());	\
+} while (0)
+
+#define preempt_enable_no_resched() do {	\
+	atomic_dec(atomic_ptr_preempt_count());	\
+} while (0)
+
+#define preempt_enable() do {			\
+	if (atomic_dec_and_test(atomic_ptr_preempt_count()) && \
+			current->need_resched)	\
+		preempt_schedule();		\
+} while (0)
+
+#define spin_lock(lock) do {	\
+	preempt_disable();	\
+	_raw_spin_lock(lock);	\
+} while(0)
+
+#define spin_trylock(lock) ({preempt_disable(); _raw_spin_trylock(lock) ? \
+	1 : ({preempt_enable(); 0;});})
+
+#define spin_unlock(lock) do {	\
+	_raw_spin_unlock(lock);	\
+	preempt_enable();	\
+} while (0)
+
+#define read_lock(lock)		({preempt_disable(); _raw_read_lock(lock);})
+#define read_unlock(lock)	({_raw_read_unlock(lock); preempt_enable();})
+#define write_lock(lock)	({preempt_disable(); _raw_write_lock(lock);})
+#define write_unlock(lock)	({_raw_write_unlock(lock); preempt_enable();})
+#define write_trylock(lock)	({preempt_disable(); _raw_write_trylock(lock) ? \
+	1 : ({preempt_enable(); 0;});})
+
+#else /* CONFIG_PREEMPT */
+
+#define preempt_is_disable() do { } while (0)
+#define preempt_disable()    do { } while (0)
+#define preempt_enable_no_resched()
+#define preempt_enable()     do { } while (0)
+#define preempt_prefetch(a)
+
+#define spin_lock(lock)		_raw_spin_lock(lock)
+#define spin_trylock(lock)	_raw_spin_trylock(lock)
+#define spin_unlock(lock)	_raw_spin_unlock(lock)
+
+#define read_lock(lock)		_raw_read_lock(lock)
+#define read_unlock(lock)	_raw_read_unlock(lock)
+#define write_lock(lock)	_raw_write_lock(lock)
+#define write_unlock(lock)	_raw_write_unlock(lock)
+#define write_trylock(lock)	_raw_write_trylock(lock)
+#endif /* !CONFIG_PREEMPT */
 
 /* "lock on reference count zero" */
 #ifndef atomic_dec_and_lock
diff -urN linux-2.4.10/include/linux/tqueue.h linux/include/linux/tqueue.h
--- linux-2.4.10/include/linux/tqueue.h	Sat Oct 20 03:20:24 2001
+++ linux/include/linux/tqueue.h	Sat Oct 20 03:21:15 2001
@@ -94,6 +94,22 @@
 extern spinlock_t tqueue_lock;
 
 /*
+ * Call all "bottom halfs" on a given list.
+ */
+
+extern void __run_task_queue(task_queue *list);
+
+static inline void run_task_queue(task_queue *list)
+{
+	if (TQ_ACTIVE(*list))
+		__run_task_queue(list);
+}
+
+#endif /* _LINUX_TQUEUE_H */
+
+#if !defined(_LINUX_TQUEUE_H_INLINES) && defined(_TASK_STRUCT_DEFINED)
+#define _LINUX_TQUEUE_H_INLINES
+/*
  * Queue a task on a tq.  Return non-zero if it was successfully
  * added.
  */
@@ -109,17 +125,4 @@
 	}
 	return ret;
 }
-
-/*
- * Call all "bottom halfs" on a given list.
- */
-
-extern void __run_task_queue(task_queue *list);
-
-static inline void run_task_queue(task_queue *list)
-{
-	if (TQ_ACTIVE(*list))
-		__run_task_queue(list);
-}
-
-#endif /* _LINUX_TQUEUE_H */
+#endif
diff -urN linux-2.4.10/kernel/exit.c linux/kernel/exit.c
--- linux-2.4.10/kernel/exit.c	Sat Oct 20 03:20:24 2001
+++ linux/kernel/exit.c	Sat Oct 20 03:21:15 2001
@@ -279,6 +279,10 @@
 struct mm_struct * start_lazy_tlb(void)
 {
 	struct mm_struct *mm = current->mm;
+#ifdef CONFIG_PREEMPT
+	if (preempt_is_disable() == 0)
+		BUG();
+#endif
 	current->mm = NULL;
 	/* active_mm is still 'mm' */
 	atomic_inc(&mm->mm_count);
@@ -290,6 +294,10 @@
 {
 	struct mm_struct *active_mm = current->active_mm;
 
+#ifdef CONFIG_PREEMPT
+	if (preempt_is_disable() == 0)
+		BUG();
+#endif
 	current->mm = mm;
 	if (mm != active_mm) {
 		current->active_mm = mm;
@@ -313,8 +321,8 @@
 		/* more a memory barrier than a real lock */
 		task_lock(tsk);
 		tsk->mm = NULL;
-		task_unlock(tsk);
 		enter_lazy_tlb(mm, current, smp_processor_id());
+		task_unlock(tsk);
 		mmput(mm);
 	}
 }
diff -urN linux-2.4.10/kernel/fork.c linux/kernel/fork.c
--- linux-2.4.10/kernel/fork.c	Sat Oct 20 03:20:24 2001
+++ linux/kernel/fork.c	Sat Oct 20 03:21:15 2001
@@ -604,6 +604,12 @@
 	if (p->binfmt && p->binfmt->module)
 		__MOD_INC_USE_COUNT(p->binfmt->module);
 
+#ifdef CONFIG_PREEMPT
+        /* Since we are keeping the context switch off state as part
+         * of the context, make sure we start with it off.
+         */
+	p->preempt_count.counter = 1;
+#endif
 	p->did_exec = 0;
 	p->swappable = 0;
 	p->state = TASK_UNINTERRUPTIBLE;
diff -urN linux-2.4.10/kernel/ksyms.c linux/kernel/ksyms.c
--- linux-2.4.10/kernel/ksyms.c	Sat Oct 20 03:20:24 2001
+++ linux/kernel/ksyms.c	Sat Oct 20 03:21:15 2001
@@ -431,6 +431,9 @@
 EXPORT_SYMBOL(interruptible_sleep_on);
 EXPORT_SYMBOL(interruptible_sleep_on_timeout);
 EXPORT_SYMBOL(schedule);
+#ifdef CONFIG_PREEMPT
+EXPORT_SYMBOL(preempt_schedule);
+#endif
 EXPORT_SYMBOL(schedule_timeout);
 EXPORT_SYMBOL(jiffies);
 EXPORT_SYMBOL(xtime);
diff -urN linux-2.4.10/kernel/sched.c linux/kernel/sched.c
--- linux-2.4.10/kernel/sched.c	Sat Oct 20 03:20:24 2001
+++ linux/kernel/sched.c	Sat Oct 20 03:21:15 2001
@@ -475,7 +475,7 @@
 	task_lock(prev);
 	prev->has_cpu = 0;
 	mb();
-	if (prev->state == TASK_RUNNING)
+	if (task_on_runqueue(prev))
 		goto needs_resched;
 
 out_unlock:
@@ -505,7 +505,7 @@
 			goto out_unlock;
 
 		spin_lock_irqsave(&runqueue_lock, flags);
-		if ((prev->state == TASK_RUNNING) && !prev->has_cpu)
+		if (task_on_runqueue(prev) && !prev->has_cpu)
 			reschedule_idle(prev);
 		spin_unlock_irqrestore(&runqueue_lock, flags);
 		goto out_unlock;
@@ -518,6 +518,9 @@
 void schedule_tail(struct task_struct *prev)
 {
 	__schedule_tail(prev);
+#ifdef CONFIG_PREEMPT
+	preempt_enable();
+#endif
 }
 
 /*
@@ -540,6 +543,10 @@
 
 	spin_lock_prefetch(&runqueue_lock);
 
+#ifdef CONFIG_PREEMPT
+	preempt_disable(); 
+#endif
+
 	if (!current->active_mm) BUG();
 need_resched_back:
 	prev = current;
@@ -563,6 +570,9 @@
 		goto move_rr_last;
 move_rr_back:
 
+#ifdef CONFIG_PREEMPT
+	if (preempt_is_disable() & PREEMPT_ACTIVE) goto treat_like_run;
+#endif
 	switch (prev->state) {
 		case TASK_INTERRUPTIBLE:
 			if (signal_pending(prev)) {
@@ -573,6 +583,9 @@
 			del_from_runqueue(prev);
 		case TASK_RUNNING:;
 	}
+#ifdef CONFIG_PREEMPT
+	treat_like_run:
+#endif
 	prev->need_resched = 0;
 
 	/*
@@ -585,7 +598,7 @@
 	 */
 	next = idle_task(this_cpu);
 	c = -1000;
-	if (prev->state == TASK_RUNNING)
+	if (task_on_runqueue(prev))
 		goto still_running;
 
 still_running_back:
@@ -679,6 +692,9 @@
 	if (current->need_resched)
 		goto need_resched_back;
 
+#ifdef CONFIG_PREEMPT
+	preempt_enable_no_resched(); 
+#endif
 	return;
 
 recalculate:
@@ -1076,6 +1092,32 @@
 	return 0;
 }
 
+#ifdef CONFIG_PREEMPT
+
+#ifdef CONFIG_SMP
+#define lock_to_this_cpu()				\
+        int old_cpus_allowed = current->cpus_allowed;	\
+        current->cpus_allowed = 1 << smp_processor_id()
+#define restore_cpus_allowed() current->cpus_allowed = old_cpus_allowed;
+#else
+#define lock_to_this_cpu()
+#define restore_cpus_allowed()
+#endif /* !CONFIG_SMP */
+
+asmlinkage void preempt_schedule(void)
+{
+	while (current->need_resched) {
+		/* it would be ideal not to lock tasks to their cpu here,
+		 * but only around the data that needs such locking */
+		lock_to_this_cpu();
+		atomic_add(PREEMPT_ACTIVE + 1, &switch_lock_count());
+		schedule();
+		restore_cpus_allowed();
+		atomic_sub(PREEMPT_ACTIVE + 1, &switch_lock_count());
+	}
+}
+#endif /* CONFIG_PREEMPT */
+
 asmlinkage long sys_sched_get_priority_max(int policy)
 {
 	int ret = -EINVAL;
diff -urN linux-2.4.10/lib/dec_and_lock.c linux/lib/dec_and_lock.c
--- linux-2.4.10/lib/dec_and_lock.c	Sat Oct 20 03:20:24 2001
+++ linux/lib/dec_and_lock.c	Sat Oct 20 03:21:15 2001
@@ -1,5 +1,6 @@
 #include <linux/module.h>
 #include <linux/spinlock.h>
+#include <linux/sched.h>
 #include <asm/atomic.h>
 
 /*
diff -urN linux-2.4.10/net/socket.c linux/net/socket.c
--- linux-2.4.10/net/socket.c	Sat Oct 20 03:20:25 2001
+++ linux/net/socket.c	Sat Oct 20 03:21:15 2001
@@ -135,7 +135,7 @@
 
 static struct net_proto_family *net_families[NPROTO];
 
-#ifdef CONFIG_SMP
+#if defined(CONFIG_SMP) || defined(CONFIG_PREEMPT)
 static atomic_t net_family_lockct = ATOMIC_INIT(0);
 static spinlock_t net_family_lock = SPIN_LOCK_UNLOCKED;