diff -urN linux-2.4.18/CREDITS linux/CREDITS
--- linux-2.4.18/CREDITS	Tue May  7 09:35:21 2002
+++ linux/CREDITS	Thu May 30 09:41:22 2002
@@ -981,8 +981,8 @@
 
 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-2.4.18/Documentation/Configure.help linux/Documentation/Configure.help
--- linux-2.4.18/Documentation/Configure.help	Tue May  7 09:36:19 2002
+++ linux/Documentation/Configure.help	Thu May 30 09:41:22 2002
@@ -266,6 +266,17 @@
   If you have a system with several CPUs, you do not need to say Y
   here: the local 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.
+
+  Say Y here if you are building a kernel for a desktop, embedded or
+  real-time 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-2.4.18/Documentation/preempt-locking.txt linux/Documentation/preempt-locking.txt
--- linux-2.4.18/Documentation/preempt-locking.txt	Wed Dec 31 16:00:00 1969
+++ linux/Documentation/preempt-locking.txt	Thu May 30 09:41:22 2002
@@ -0,0 +1,104 @@
+		  Proper Locking Under a Preemptible Kernel:
+		       Keeping Kernel Code Preempt-Safe
+			  Robert Love <rml@tech9.net>
+			   Last Updated: 22 Jan 2002
+
+
+INTRODUCTION
+
+
+A preemptible kernel creates new locking issues.  The issues are the same as
+those under SMP: concurrency and reentrancy.  Thankfully, the Linux preemptible
+kernel model leverages existing SMP locking mechanisms.  Thus, the kernel
+requires explicit additional locking for very few additional situations.
+
+This document is for all kernel hackers.  Developing code in the kernel
+requires protecting these situations.
+ 
+
+RULE #1: Per-CPU data structures need explicit protection
+
+
+Two similar problems arise. An example code snippet:
+
+	struct this_needs_locking tux[NR_CPUS];
+	tux[smp_processor_id()] = some_value;
+	/* task is preempted here... */
+	something = tux[smp_processor_id()];
+
+First, since the data is per-CPU, it may not have explicit SMP locking, but
+require it otherwise.  Second, when a preempted task is finally rescheduled,
+the previous value of smp_processor_id may not equal the current.  You must
+protect these situations by disabling preemption around them.
+
+
+RULE #2: CPU state must be protected.
+
+
+Under preemption, the state of the CPU must be protected.  This is arch-
+dependent, but includes CPU structures and state not preserved over a context
+switch.  For example, on x86, entering and exiting FPU mode is now a critical
+section that must occur while preemption is disabled.  Think what would happen
+if the kernel is executing a floating-point instruction and is then preempted.
+Remember, the kernel does not save FPU state except for user tasks.  Therefore,
+upon preemption, the FPU registers will be sold to the lowest bidder.  Thus,
+preemption must be disabled around such regions.
+
+Note, some FPU functions are already explicitly preempt safe.  For example,
+kernel_fpu_begin and kernel_fpu_end will disable and enable preemption.
+However, math_state_restore must be called with preemption disabled.
+
+
+RULE #3: Lock acquire and release must be performed by same task
+
+
+A lock acquired in one task must be released by the same task.  This
+means you can't do oddball things like acquire a lock and go off to
+play while another task releases it.  If you want to do something
+like this, acquire and release the task in the same code path and
+have the caller wait on an event by the other task.
+
+
+SOLUTION
+
+
+Data protection under preemption is achieved by disabling preemption for the
+duration of the critical region.
+
+preempt_enable()		decrement the preempt counter
+preempt_disable()		increment the preempt counter
+preempt_enable_no_resched()	decrement, but do not immediately preempt
+preempt_get_count()		return the preempt counter
+
+The functions are nestable.  In other words, you can call preempt_disable
+n-times in a code path, and preemption will not be reenabled until the n-th
+call to preempt_enable.  The preempt statements define to nothing if
+preemption is not enabled.
+
+Note that you do not need to explicitly prevent preemption if you are holding
+any locks or interrupts are disabled, since preemption is implicitly disabled
+in those cases.
+
+Example:
+
+	cpucache_t *cc; /* this is per-CPU */
+	preempt_disable();
+	cc = cc_data(searchp);
+	if (cc && cc->avail) {
+		__free_block(searchp, cc_entry(cc), cc->avail);
+		cc->avail = 0;
+	}
+	preempt_enable();
+	return 0;
+
+Notice how the preemption statements must encompass every reference of the
+critical variables.  Another example:
+
+	int buf[NR_CPUS];
+	set_cpu_val(buf);
+	if (buf[smp_processor_id()] == -1) printf(KERN_INFO "wee!\n");
+	spin_lock(&buf_lock);
+	/* ... */
+
+This code is not preempt-safe, but see how easily we can fix it by simply
+moving the spin_lock up two lines.
diff -urN linux-2.4.18/MAINTAINERS linux/MAINTAINERS
--- linux-2.4.18/MAINTAINERS	Tue May  7 09:35:36 2002
+++ linux/MAINTAINERS	Thu May 30 09:41:22 2002
@@ -1248,6 +1248,14 @@
 M:	mostrows@styx.uwaterloo.ca
 S:	Maintained
 
+PREEMPTIBLE KERNEL
+P:	Robert M. Love
+M:	rml@tech9.net
+L:	linux-kernel@vger.kernel.org
+L:	kpreempt-tech@lists.sourceforge.net
+W:	http://tech9.net/rml/linux
+S:	Supported
+
 PROMISE DC4030 CACHING DISK CONTROLLER DRIVER
 P:	Peter Denison
 M:	promise@pnd-pc.demon.co.uk
diff -urN linux-2.4.18/arch/arm/config.in linux/arch/arm/config.in
--- linux-2.4.18/arch/arm/config.in	Tue May  7 09:36:10 2002
+++ linux/arch/arm/config.in	Thu May 30 09:41:22 2002
@@ -329,7 +329,7 @@
 else
    define_bool CONFIG_DISCONTIGMEM n
 fi
-
+dep_bool 'Preemptible Kernel' CONFIG_PREEMPT $CONFIG_CPU_32
 endmenu
 
 mainmenu_option next_comment
diff -urN linux-2.4.18/arch/arm/kernel/entry-armv.S linux/arch/arm/kernel/entry-armv.S
--- linux-2.4.18/arch/arm/kernel/entry-armv.S	Tue May  7 09:36:10 2002
+++ linux/arch/arm/kernel/entry-armv.S	Thu May 30 09:41:22 2002
@@ -672,6 +672,12 @@
 		add	r4, sp, #S_SP
 		mov	r6, lr
 		stmia	r4, {r5, r6, r7, r8, r9}	@ save sp_SVC, lr_SVC, pc, cpsr, old_ro
+#ifdef CONFIG_PREEMPT
+		get_current_task r9
+		ldr	r8, [r9, #TSK_PREEMPT]
+		add	r8, r8, #1
+		str	r8, [r9, #TSK_PREEMPT]
+#endif
 1:		get_irqnr_and_base r0, r6, r5, lr
 		movne	r1, sp
 		@
@@ -679,6 +685,25 @@
 		@
 		adrsvc	ne, lr, 1b
 		bne	do_IRQ
+#ifdef CONFIG_PREEMPT
+2:		ldr	r8, [r9, #TSK_PREEMPT]
+		subs	r8, r8, #1
+		bne	3f
+		ldr	r7, [r9, #TSK_NEED_RESCHED]
+		teq	r7, #0
+		beq	3f
+		ldr	r6, .LCirqstat
+		ldr	r0, [r6, #IRQSTAT_BH_COUNT]
+		teq	r0, #0
+		bne	3f
+		mov	r0, #MODE_SVC
+		msr	cpsr_c, r0		@ enable interrupts
+		bl	SYMBOL_NAME(preempt_schedule)
+		mov	r0, #I_BIT | MODE_SVC
+		msr	cpsr_c, r0              @ disable interrupts
+		b	2b
+3:		str	r8, [r9, #TSK_PREEMPT]
+#endif
 		ldr	r0, [sp, #S_PSR]		@ irqs are already disabled
 		msr	spsr, r0
 		ldmia	sp, {r0 - pc}^			@ load r0 - pc, cpsr
@@ -736,6 +761,9 @@
 .LCprocfns:	.word	SYMBOL_NAME(processor)
 #endif
 .LCfp:		.word	SYMBOL_NAME(fp_enter)
+#ifdef CONFIG_PREEMPT
+.LCirqstat:	.word	SYMBOL_NAME(irq_stat)
+#endif
 
 		irq_prio_table
 
@@ -775,6 +803,12 @@
 		stmdb	r8, {sp, lr}^
 		alignment_trap r4, r7, __temp_irq
 		zero_fp
+		get_current_task tsk
+#ifdef CONFIG_PREEMPT
+		ldr	r0, [tsk, #TSK_PREEMPT]
+		add	r0, r0, #1
+		str	r0, [tsk, #TSK_PREEMPT]
+#endif
 1:		get_irqnr_and_base r0, r6, r5, lr
 		movne	r1, sp
 		adrsvc	ne, lr, 1b
@@ -782,8 +816,12 @@
 		@ routine called with r0 = irq number, r1 = struct pt_regs *
 		@
 		bne	do_IRQ
+#ifdef CONFIG_PREEMPT
+		ldr	r0, [tsk, #TSK_PREEMPT]
+		sub	r0, r0, #1
+		str	r0, [tsk, #TSK_PREEMPT]
+#endif
 		mov	why, #0
-		get_current_task tsk
 		b	ret_to_user
 
 		.align	5
diff -urN linux-2.4.18/arch/arm/tools/getconstants.c linux/arch/arm/tools/getconstants.c
--- linux-2.4.18/arch/arm/tools/getconstants.c	Tue May  7 09:36:12 2002
+++ linux/arch/arm/tools/getconstants.c	Thu May 30 09:41:22 2002
@@ -13,6 +13,7 @@
 
 #include <asm/pgtable.h>
 #include <asm/uaccess.h>
+#include <asm/hardirq.h>
 
 /*
  * Make sure that the compiler and target are compatible.
@@ -39,6 +40,11 @@
 DEFN("TSS_SAVE",		OFF_TSK(thread.save));
 DEFN("TSS_FPESAVE",		OFF_TSK(thread.fpstate.soft.save));
 
+#ifdef CONFIG_PREEMPT
+DEFN("TSK_PREEMPT",		OFF_TSK(preempt_count));
+DEFN("IRQSTAT_BH_COUNT",	(unsigned long)&(((irq_cpustat_t *)0)->__local_bh_count));
+#endif
+
 #ifdef CONFIG_CPU_32
 DEFN("TSS_DOMAIN",		OFF_TSK(thread.domain));
 
diff -urN linux-2.4.18/arch/i386/config.in linux/arch/i386/config.in
--- linux-2.4.18/arch/i386/config.in	Tue May  7 09:36:02 2002
+++ linux/arch/i386/config.in	Thu May 30 09:41:22 2002
@@ -185,6 +185,7 @@
 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 'Local APIC support on uniprocessors' CONFIG_X86_UP_APIC
    dep_bool 'IO-APIC support on uniprocessors' CONFIG_X86_UP_IOAPIC $CONFIG_X86_UP_APIC
@@ -198,9 +199,12 @@
    bool 'Multiquad NUMA system' CONFIG_MULTIQUAD
 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
 
 mainmenu_option next_comment
diff -urN linux-2.4.18/arch/i386/kernel/entry.S linux/arch/i386/kernel/entry.S
--- linux-2.4.18/arch/i386/kernel/entry.S	Tue May  7 09:36:04 2002
+++ linux/arch/i386/kernel/entry.S	Thu May 30 09:41:22 2002
@@ -71,7 +71,7 @@
  * these are offsets into the task-struct.
  */
 state		=  0
-flags		=  4
+preempt_count	=  4
 sigpending	=  8
 addr_limit	= 12
 exec_domain	= 16
@@ -79,8 +79,28 @@
 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; \
@@ -247,12 +267,30 @@
 	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:
@@ -289,6 +327,9 @@
 	GET_CURRENT(%ebx)
 	call *%edi
 	addl $8,%esp
+#ifdef CONFIG_PREEMPT
+	cli
+#endif
 	jmp ret_from_exception
 
 ENTRY(coprocessor_error)
@@ -308,12 +349,18 @@
 	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-2.4.18/arch/i386/kernel/i387.c linux/arch/i386/kernel/i387.c
--- linux-2.4.18/arch/i386/kernel/i387.c	Tue May  7 09:36:04 2002
+++ linux/arch/i386/kernel/i387.c	Thu May 30 09:41:22 2002
@@ -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-2.4.18/arch/i386/kernel/smp.c linux/arch/i386/kernel/smp.c
--- linux-2.4.18/arch/i386/kernel/smp.c	Tue May  7 09:36:04 2002
+++ linux/arch/i386/kernel/smp.c	Thu May 30 09:41:22 2002
@@ -354,10 +354,13 @@
 
 asmlinkage void smp_invalidate_interrupt (void)
 {
-	unsigned long cpu = smp_processor_id();
+	unsigned long cpu;
+        
+	preempt_disable();
 
+	cpu = smp_processor_id();
 	if (!test_bit(cpu, &flush_cpumask))
-		return;
+		goto out;
 		/* 
 		 * This was a BUG() but until someone can quote me the
 		 * line from the intel manual that guarantees an IPI to
@@ -378,6 +381,8 @@
 	}
 	ack_APIC_irq();
 	clear_bit(cpu, &flush_cpumask);
+out:
+	preempt_enable();
 }
 
 static void flush_tlb_others (unsigned long cpumask, struct mm_struct *mm,
@@ -427,17 +432,22 @@
 void flush_tlb_current_task(void)
 {
 	struct mm_struct *mm = current->mm;
-	unsigned long cpu_mask = mm->cpu_vm_mask & ~(1 << smp_processor_id());
+	unsigned long cpu_mask;
 
+        preempt_disable();
+        cpu_mask = mm->cpu_vm_mask & ~(1UL << smp_processor_id());
 	local_flush_tlb();
 	if (cpu_mask)
 		flush_tlb_others(cpu_mask, mm, FLUSH_ALL);
+        preempt_enable();
 }
 
 void flush_tlb_mm (struct mm_struct * mm)
 {
-	unsigned long cpu_mask = mm->cpu_vm_mask & ~(1 << smp_processor_id());
+	unsigned long cpu_mask;
 
+        preempt_disable();
+        cpu_mask = mm->cpu_vm_mask & ~(1UL << smp_processor_id());
 	if (current->active_mm == mm) {
 		if (current->mm)
 			local_flush_tlb();
@@ -446,13 +456,16 @@
 	}
 	if (cpu_mask)
 		flush_tlb_others(cpu_mask, mm, FLUSH_ALL);
+        preempt_enable();
 }
 
 void flush_tlb_page(struct vm_area_struct * vma, unsigned long va)
 {
 	struct mm_struct *mm = vma->vm_mm;
-	unsigned long cpu_mask = mm->cpu_vm_mask & ~(1 << smp_processor_id());
+	unsigned long cpu_mask;
 
+        preempt_disable();
+        cpu_mask = mm->cpu_vm_mask & ~(1UL << smp_processor_id());
 	if (current->active_mm == mm) {
 		if(current->mm)
 			__flush_tlb_one(va);
@@ -462,6 +475,7 @@
 
 	if (cpu_mask)
 		flush_tlb_others(cpu_mask, mm, va);
+        preempt_enable();
 }
 
 static inline void do_flush_tlb_all_local(void)
diff -urN linux-2.4.18/arch/i386/kernel/traps.c linux/arch/i386/kernel/traps.c
--- linux-2.4.18/arch/i386/kernel/traps.c	Tue May  7 09:36:04 2002
+++ linux/arch/i386/kernel/traps.c	Thu May 30 09:41:22 2002
@@ -694,6 +694,8 @@
  *
  * Careful.. There are problems with IBM-designed IRQ13 behaviour.
  * Don't touch unless you *really* know how it works.
+ *
+ * Must be called with kernel preemption disabled.
  */
 asmlinkage void math_state_restore(struct pt_regs regs)
 {
diff -urN linux-2.4.18/arch/i386/lib/dec_and_lock.c linux/arch/i386/lib/dec_and_lock.c
--- linux-2.4.18/arch/i386/lib/dec_and_lock.c	Tue May  7 09:36:04 2002
+++ linux/arch/i386/lib/dec_and_lock.c	Thu May 30 09:41:22 2002
@@ -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-2.4.18/arch/sh/config.in linux/arch/sh/config.in
--- linux-2.4.18/arch/sh/config.in	Tue May  7 09:36:13 2002
+++ linux/arch/sh/config.in	Thu May 30 09:41:22 2002
@@ -124,6 +124,7 @@
    hex 'Physical memory start address' CONFIG_MEMORY_START 08000000
    hex 'Physical memory size' CONFIG_MEMORY_SIZE 00400000
 fi
+bool 'Preemptible Kernel' CONFIG_PREEMPT
 endmenu
 
 if [ "$CONFIG_SH_HP690" = "y" ]; then
diff -urN linux-2.4.18/arch/sh/kernel/entry.S linux/arch/sh/kernel/entry.S
--- linux-2.4.18/arch/sh/kernel/entry.S	Tue May  7 09:36:14 2002
+++ linux/arch/sh/kernel/entry.S	Thu May 30 09:41:22 2002
@@ -60,10 +60,18 @@
 /*
  * These are offsets into the task-struct.
  */
-flags		=  4
+preempt_count	=  4
 sigpending	=  8
 need_resched	= 20
 tsk_ptrace	= 24
+flags		= 84
+
+/*
+ * These offsets are into irq_stat.
+ * (Find irq_cpustat_t in asm-sh/hardirq.h)
+ */
+local_irq_count =  8
+local_bh_count  = 12
 
 PT_TRACESYS  = 0x00000002
 PF_USEDFPU   = 0x00100000
@@ -143,7 +151,7 @@
 	mov.l	__INV_IMASK, r11;	\
 	stc	sr, r10;		\
 	and	r11, r10;		\
-	stc	k_g_imask, r11;	\
+	stc	k_g_imask, r11;		\
 	or	r11, r10;		\
 	ldc	r10, sr
 
@@ -304,8 +312,8 @@
 	mov.l	@(tsk_ptrace,r0), r0	! Is current PTRACE_SYSCALL'd?
 	mov	#PT_TRACESYS, r1
 	tst	r1, r0
-	bt	ret_from_syscall
-	bra	syscall_ret_trace
+	bf	syscall_ret_trace
+	bra	ret_from_syscall
 	 nop	 
 
 	.align	2
@@ -505,8 +513,6 @@
 	.long	syscall_ret_trace
 __syscall_ret:
 	.long	syscall_ret
-__INV_IMASK:
-	.long	0xffffff0f	! ~(IMASK)
 
 
 	.align	2
@@ -518,7 +524,84 @@
 	.align	2
 1:	.long	SYMBOL_NAME(schedule)
 
+#ifdef CONFIG_PREEMPT	
+	!
+	! Returning from interrupt during kernel mode: check if
+	! preempt_schedule should be called. If need_resched flag
+	! is set, preempt_count is zero, and we're not currently
+	! in an interrupt handler (local irq or bottom half) then
+	! call preempt_schedule. 
+	!
+	! Increment preempt_count to prevent a nested interrupt
+	! from reentering preempt_schedule, then decrement after
+	! and drop through to regular interrupt return which will
+	! jump back and check again in case such an interrupt did
+	! come in (and didn't preempt due to preempt_count).
+	!
+	! NOTE:	because we just checked that preempt_count was
+	! zero before getting to the call, can't we use immediate
+	! values (1 and 0) rather than inc/dec? Also, rather than
+	! drop through to ret_from_irq, we already know this thread
+	! is kernel mode, can't we go direct to ret_from_kirq? In
+	! fact, with proper interrupt nesting and so forth could
+	! the loop simply be on the need_resched w/o checking the
+	! other stuff again? Optimize later...
+	!
+	.align	2
+ret_from_kirq:
+	! Nonzero preempt_count prevents scheduling
+	stc	k_current, r1
+	mov.l	@(preempt_count,r1), r0
+	cmp/eq	#0, r0
+	bf	restore_all
+	! Zero need_resched prevents scheduling
+	mov.l	@(need_resched,r1), r0
+	cmp/eq	#0, r0
+	bt	restore_all
+	! If in_interrupt(), don't schedule
+	mov.l	__irq_stat, r1
+	mov.l	@(local_irq_count,r1), r0
+	mov.l	@(local_bh_count,r1), r1
+	or	r1, r0
+	cmp/eq	#0, r0
+	bf	restore_all
+	! Allow scheduling using preempt_schedule
+	! Adjust preempt_count and SR as needed.
+	stc	k_current, r1
+	mov.l	@(preempt_count,r1), r0	! Could replace this ...
+	add	#1, r0			! ... and this w/mov #1?
+	mov.l	r0, @(preempt_count,r1)
+	STI()
+	mov.l	__preempt_schedule, r0
+	jsr	@r0
+	 nop	
+	/* CLI */
+	stc	sr, r0
+	or	#0xf0, r0
+	ldc	r0, sr
+	!
+	stc	k_current, r1
+	mov.l	@(preempt_count,r1), r0	! Could replace this ...
+	add	#-1, r0			! ... and this w/mov #0?
+	mov.l	r0, @(preempt_count,r1)
+	! Maybe should bra ret_from_kirq, or loop over need_resched?
+	! For now, fall through to ret_from_irq again...
+#endif /* CONFIG_PREEMPT */
+	
 ret_from_irq:
+	mov	#OFF_SR, r0
+	mov.l	@(r0,r15), r0	! get status register
+	shll	r0
+	shll	r0		! kernel space?
+#ifndef CONFIG_PREEMPT
+	bt	restore_all	! Yes, it's from kernel, go back soon
+#else /* CONFIG_PREEMPT */
+	bt	ret_from_kirq	! From kernel: maybe preempt_schedule
+#endif /* CONFIG_PREEMPT */
+	!
+	bra	ret_from_syscall
+	 nop
+
 ret_from_exception:
 	mov	#OFF_SR, r0
 	mov.l	@(r0,r15), r0	! get status register
@@ -564,6 +647,13 @@
 	.long	SYMBOL_NAME(do_signal)
 __irq_stat:
 	.long	SYMBOL_NAME(irq_stat)
+#ifdef CONFIG_PREEMPT
+__preempt_schedule:
+	.long	SYMBOL_NAME(preempt_schedule)
+#endif /* CONFIG_PREEMPT */	
+__INV_IMASK:
+	.long	0xffffff0f	! ~(IMASK)
+
 
 	.align 2
 restore_all:
@@ -679,7 +769,7 @@
 __fpu_prepare_fd:
 	.long	SYMBOL_NAME(fpu_prepare_fd)
 __init_task_flags:
-	.long	SYMBOL_NAME(init_task_union)+4
+	.long	SYMBOL_NAME(init_task_union)+flags
 __PF_USEDFPU:
 	.long	PF_USEDFPU
 #endif
diff -urN linux-2.4.18/arch/sh/kernel/irq.c linux/arch/sh/kernel/irq.c
--- linux-2.4.18/arch/sh/kernel/irq.c	Tue May  7 09:36:14 2002
+++ linux/arch/sh/kernel/irq.c	Thu May 30 09:41:22 2002
@@ -229,6 +229,14 @@
 	struct irqaction * action;
 	unsigned int status;
 
+	/*
+	 * At this point we're now about to actually call handlers,
+	 * and interrupts might get reenabled during them... bump
+	 * preempt_count to prevent any preemption while the handler
+ 	 * called here is pending...
+ 	 */
+ 	preempt_disable();
+
 	/* Get IRQ number */
 	asm volatile("stc	r2_bank, %0\n\t"
 		     "shlr2	%0\n\t"
@@ -298,8 +306,17 @@
 	desc->handler->end(irq);
 	spin_unlock(&desc->lock);
 
+
 	if (softirq_pending(cpu))
 		do_softirq();
+
+	/*
+	 * We're done with the handlers, interrupts should be
+	 * currently disabled; decrement preempt_count now so
+	 * as we return preemption may be allowed...
+	 */
+	preempt_enable_no_resched();
+
 	return 1;
 }
 
diff -urN linux-2.4.18/drivers/ieee1394/csr.c linux/drivers/ieee1394/csr.c
--- linux-2.4.18/drivers/ieee1394/csr.c	Tue May  7 09:35:59 2002
+++ linux/drivers/ieee1394/csr.c	Thu May 30 09:41:22 2002
@@ -10,6 +10,7 @@
  */
 
 #include <linux/string.h>
+#include <linux/sched.h>
 
 #include "ieee1394_types.h"
 #include "hosts.h"
diff -urN linux-2.4.18/drivers/sound/sound_core.c linux/drivers/sound/sound_core.c
--- linux-2.4.18/drivers/sound/sound_core.c	Tue May  7 09:35:49 2002
+++ linux/drivers/sound/sound_core.c	Thu May 30 09:41:22 2002
@@ -37,6 +37,7 @@
 #include <linux/config.h>
 #include <linux/module.h>
 #include <linux/init.h>
+#include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/types.h>
 #include <linux/kernel.h>
diff -urN linux-2.4.18/fs/adfs/map.c linux/fs/adfs/map.c
--- linux-2.4.18/fs/adfs/map.c	Tue May  7 09:35:19 2002
+++ linux/fs/adfs/map.c	Thu May 30 09:41:22 2002
@@ -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-2.4.18/fs/exec.c linux/fs/exec.c
--- linux-2.4.18/fs/exec.c	Tue May  7 09:35:18 2002
+++ linux/fs/exec.c	Thu May 30 09:41:22 2002
@@ -420,8 +420,8 @@
 		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-2.4.18/fs/fat/cache.c linux/fs/fat/cache.c
--- linux-2.4.18/fs/fat/cache.c	Tue May  7 09:35:18 2002
+++ linux/fs/fat/cache.c	Thu May 30 09:41:23 2002
@@ -14,6 +14,7 @@
 #include <linux/string.h>
 #include <linux/stat.h>
 #include <linux/fat_cvf.h>
+#include <linux/sched.h>
 
 #if 0
 #  define PRINTK(x) printk x
diff -urN linux-2.4.18/fs/nls/nls_base.c linux/fs/nls/nls_base.c
--- linux-2.4.18/fs/nls/nls_base.c	Tue May  7 09:35:19 2002
+++ linux/fs/nls/nls_base.c	Thu May 30 09:41:23 2002
@@ -18,6 +18,7 @@
 #ifdef CONFIG_KMOD
 #include <linux/kmod.h>
 #endif
+#include <linux/sched.h>
 #include <linux/spinlock.h>
 
 static struct nls_table *tables;
diff -urN linux-2.4.18/include/asm-arm/dma.h linux/include/asm-arm/dma.h
--- linux-2.4.18/include/asm-arm/dma.h	Tue May  7 09:35:27 2002
+++ linux/include/asm-arm/dma.h	Thu May 30 09:41:23 2002
@@ -5,6 +5,7 @@
 
 #include <linux/config.h>
 #include <linux/spinlock.h>
+#include <linux/sched.h>
 #include <asm/system.h>
 #include <asm/memory.h>
 #include <asm/scatterlist.h>
diff -urN linux-2.4.18/include/asm-arm/hardirq.h linux/include/asm-arm/hardirq.h
--- linux-2.4.18/include/asm-arm/hardirq.h	Tue May  7 09:35:27 2002
+++ linux/include/asm-arm/hardirq.h	Thu May 30 09:41:23 2002
@@ -34,6 +34,7 @@
 #define irq_exit(cpu,irq)	(local_irq_count(cpu)--)
 
 #define synchronize_irq()	do { } while (0)
+#define release_irqlock(cpu)	do { } while (0)
 
 #else
 #error SMP not supported
diff -urN linux-2.4.18/include/asm-arm/pgalloc.h linux/include/asm-arm/pgalloc.h
--- linux-2.4.18/include/asm-arm/pgalloc.h	Tue May  7 09:35:27 2002
+++ linux/include/asm-arm/pgalloc.h	Thu May 30 09:41:23 2002
@@ -57,40 +57,48 @@
 {
 	unsigned long *ret;
 
+	preempt_disable();
 	if ((ret = pgd_quicklist) != NULL) {
 		pgd_quicklist = (unsigned long *)__pgd_next(ret);
 		ret[1] = ret[2];
 		clean_dcache_entry(ret + 1);
 		pgtable_cache_size--;
 	}
+	preempt_enable();
 	return (pgd_t *)ret;
 }
 
 static inline void free_pgd_fast(pgd_t *pgd)
 {
+	preempt_disable();
 	__pgd_next(pgd) = (unsigned long) pgd_quicklist;
 	pgd_quicklist = (unsigned long *) pgd;
 	pgtable_cache_size++;
+	preempt_enable();
 }
 
 static inline pte_t *pte_alloc_one_fast(struct mm_struct *mm, unsigned long address)
 {
 	unsigned long *ret;
 
+	preempt_disable();
 	if((ret = pte_quicklist) != NULL) {
 		pte_quicklist = (unsigned long *)__pte_next(ret);
 		ret[0] = 0;
 		clean_dcache_entry(ret);
 		pgtable_cache_size--;
 	}
+	preempt_enable();
 	return (pte_t *)ret;
 }
 
 static inline void free_pte_fast(pte_t *pte)
 {
+	preempt_disable();
 	__pte_next(pte) = (unsigned long) pte_quicklist;
 	pte_quicklist = (unsigned long *) pte;
 	pgtable_cache_size++;
+	preempt_enable();
 }
 
 #else	/* CONFIG_NO_PGT_CACHE */
diff -urN linux-2.4.18/include/asm-arm/smplock.h linux/include/asm-arm/smplock.h
--- linux-2.4.18/include/asm-arm/smplock.h	Tue May  7 09:35:27 2002
+++ linux/include/asm-arm/smplock.h	Thu May 30 09:41:23 2002
@@ -3,12 +3,17 @@
  *
  * Default SMP lock implementation
  */
+#include <linux/config.h>
 #include <linux/interrupt.h>
 #include <linux/spinlock.h>
 
 extern spinlock_t kernel_flag;
 
+#ifdef CONFIG_PREEMPT
+#define kernel_locked()		preempt_get_count()
+#else
 #define kernel_locked()		spin_is_locked(&kernel_flag)
+#endif
 
 /*
  * Release global kernel lock and global interrupt lock
@@ -40,8 +45,14 @@
  */
 static inline void lock_kernel(void)
 {
+#ifdef CONFIG_PREEMPT
+	if (current->lock_depth == -1)
+		spin_lock(&kernel_flag);
+	++current->lock_depth;
+#else
 	if (!++current->lock_depth)
 		spin_lock(&kernel_flag);
+#endif
 }
 
 static inline void unlock_kernel(void)
diff -urN linux-2.4.18/include/asm-arm/softirq.h linux/include/asm-arm/softirq.h
--- linux-2.4.18/include/asm-arm/softirq.h	Tue May  7 09:35:27 2002
+++ linux/include/asm-arm/softirq.h	Thu May 30 09:41:23 2002
@@ -5,20 +5,22 @@
 #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())
 
 #define in_softirq()		(local_bh_count(smp_processor_id()) != 0)
 
-#define local_bh_enable()						\
+#define _local_bh_enable()						\
 do {									\
 	unsigned int *ptr = &local_bh_count(smp_processor_id());	\
 	if (!--*ptr && ptr[-2])						\
 		__asm__("bl%? __do_softirq": : : "lr");/* out of line */\
 } while (0)
 
+#define local_bh_enable() do { _local_bh_enable(); preempt_enable(); } while (0)
+
 #endif	/* __ASM_SOFTIRQ_H */
diff -urN linux-2.4.18/include/asm-i386/hardirq.h linux/include/asm-i386/hardirq.h
--- linux-2.4.18/include/asm-i386/hardirq.h	Tue May  7 09:35:23 2002
+++ linux/include/asm-i386/hardirq.h	Thu May 30 09:41:23 2002
@@ -19,12 +19,16 @@
 
 /*
  * Are we in an interrupt context? Either doing bottom half
- * or hardware interrupt processing?
+ * or hardware interrupt processing?  Note the preempt check,
+ * this is both a bugfix and an optimization.  If we are
+ * preemptible, we cannot be in an interrupt.
  */
-#define in_interrupt() ({ int __cpu = smp_processor_id(); \
-	(local_irq_count(__cpu) + local_bh_count(__cpu) != 0); })
+#define in_interrupt() (preempt_is_disabled() && \
+	({unsigned long __cpu = smp_processor_id(); \
+	(local_irq_count(__cpu) + local_bh_count(__cpu) != 0); }))
 
-#define in_irq() (local_irq_count(smp_processor_id()) != 0)
+#define in_irq() (preempt_is_disabled() && \
+        (local_irq_count(smp_processor_id()) != 0))
 
 #ifndef CONFIG_SMP
 
@@ -36,6 +40,8 @@
 
 #define synchronize_irq()	barrier()
 
+#define release_irqlock(cpu)	do { } while (0)
+
 #else
 
 #include <asm/atomic.h>
diff -urN linux-2.4.18/include/asm-i386/highmem.h linux/include/asm-i386/highmem.h
--- linux-2.4.18/include/asm-i386/highmem.h	Tue May  7 09:35:23 2002
+++ linux/include/asm-i386/highmem.h	Thu May 30 09:41:23 2002
@@ -88,6 +88,7 @@
 	enum fixed_addresses idx;
 	unsigned long vaddr;
 
+	preempt_disable();
 	if (page < highmem_start_page)
 		return page_address(page);
 
@@ -109,8 +110,10 @@
 	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();
@@ -122,6 +125,8 @@
 	pte_clear(kmap_pte-idx);
 	__flush_tlb_one(vaddr);
 #endif
+
+	preempt_enable();
 }
 
 #endif /* __KERNEL__ */
diff -urN linux-2.4.18/include/asm-i386/hw_irq.h linux/include/asm-i386/hw_irq.h
--- linux-2.4.18/include/asm-i386/hw_irq.h	Tue May  7 09:35:23 2002
+++ linux/include/asm-i386/hw_irq.h	Thu May 30 09:41:23 2002
@@ -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_LOCK_COUNT \
+	GET_CURRENT \
+	"incl 4(%ebx)\n\t"
+#else
+#define BUMP_LOCK_COUNT
+#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_LOCK_COUNT
 
 #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-2.4.18/include/asm-i386/i387.h linux/include/asm-i386/i387.h
--- linux-2.4.18/include/asm-i386/i387.h	Tue May  7 09:35:23 2002
+++ linux/include/asm-i386/i387.h	Thu May 30 09:41:23 2002
@@ -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-2.4.18/include/asm-i386/pgalloc.h linux/include/asm-i386/pgalloc.h
--- linux-2.4.18/include/asm-i386/pgalloc.h	Tue May  7 09:35:23 2002
+++ linux/include/asm-i386/pgalloc.h	Thu May 30 09:41:23 2002
@@ -75,20 +75,26 @@
 {
 	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)
@@ -119,19 +125,23 @@
 {
 	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-2.4.18/include/asm-i386/smplock.h linux/include/asm-i386/smplock.h
--- linux-2.4.18/include/asm-i386/smplock.h	Tue May  7 09:35:23 2002
+++ linux/include/asm-i386/smplock.h	Thu May 30 09:41:23 2002
@@ -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_get_count()
+#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-2.4.18/include/asm-i386/softirq.h linux/include/asm-i386/softirq.h
--- linux-2.4.18/include/asm-i386/softirq.h	Tue May  7 09:35:23 2002
+++ linux/include/asm-i386/softirq.h	Thu May 30 09:41:23 2002
@@ -6,9 +6,9 @@
 #include <linux/stringify.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())
@@ -23,7 +23,7 @@
  * 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());	\
 									\
@@ -49,4 +49,6 @@
 		/* no registers clobbered */ );				\
 } while (0)
 
+#define local_bh_enable() do { _local_bh_enable(); preempt_enable(); } while (0)
+
 #endif	/* __ASM_SOFTIRQ_H */
diff -urN linux-2.4.18/include/asm-i386/spinlock.h linux/include/asm-i386/spinlock.h
--- linux-2.4.18/include/asm-i386/spinlock.h	Tue May  7 09:35:23 2002
+++ linux/include/asm-i386/spinlock.h	Thu May 30 09:41:23 2002
@@ -81,7 +81,7 @@
 		:"=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)
@@ -101,7 +101,7 @@
 		:"=q" (oldval), "=m" (lock->lock) \
 		:"0" (oldval) : "memory"
 
-static inline void spin_unlock(spinlock_t *lock)
+static inline void _raw_spin_unlock(spinlock_t *lock)
 {
 	char oldval = 1;
 #if SPINLOCK_DEBUG
@@ -117,7 +117,7 @@
 
 #endif
 
-static inline int spin_trylock(spinlock_t *lock)
+static inline int _raw_spin_trylock(spinlock_t *lock)
 {
 	char oldval;
 	__asm__ __volatile__(
@@ -127,7 +127,7 @@
 	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;
@@ -183,7 +183,7 @@
  */
 /* 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)
@@ -192,7 +192,7 @@
 	__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)
@@ -201,10 +201,10 @@
 	__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-2.4.18/include/asm-sh/hardirq.h linux/include/asm-sh/hardirq.h
--- linux-2.4.18/include/asm-sh/hardirq.h	Tue May  7 09:35:29 2002
+++ linux/include/asm-sh/hardirq.h	Thu May 30 09:41:23 2002
@@ -34,6 +34,8 @@
 
 #define synchronize_irq()	barrier()
 
+#define release_irqlock(cpu)	do { } while (0)
+
 #else
 
 #error Super-H SMP is not available
diff -urN linux-2.4.18/include/asm-sh/smplock.h linux/include/asm-sh/smplock.h
--- linux-2.4.18/include/asm-sh/smplock.h	Tue May  7 09:35:29 2002
+++ linux/include/asm-sh/smplock.h	Thu May 30 09:41:23 2002
@@ -9,15 +9,88 @@
 
 #include <linux/config.h>
 
-#ifndef CONFIG_SMP
-
+#if !defined(CONFIG_SMP) && !defined(CONFIG_PREEMPT)
+/*
+ * Should never happen, since linux/smp_lock.h catches this case;
+ * but in case this file is included directly with neither SMP nor
+ * PREEMPT configuration, provide same dummys as linux/smp_lock.h
+ */
 #define lock_kernel()				do { } while(0)
 #define unlock_kernel()				do { } while(0)
-#define release_kernel_lock(task, cpu, depth)	((depth) = 1)
-#define reacquire_kernel_lock(task, cpu, depth)	do { } while(0)
+#define release_kernel_lock(task, cpu)		do { } while(0)
+#define reacquire_kernel_lock(task)		do { } while(0)
+#define kernel_locked()		1
+
+#else /* CONFIG_SMP || CONFIG_PREEMPT */
+
+#if CONFIG_SMP
+#error "We do not support SMP on SH yet"
+#endif
+/*
+ * Default SMP lock implementation (i.e. the i386 version)
+ */
+
+#include <linux/interrupt.h>
+#include <linux/spinlock.h>
+
+extern spinlock_t kernel_flag;
+#define lock_bkl() spin_lock(&kernel_flag)
+#define unlock_bkl() spin_unlock(&kernel_flag)
 
+#ifdef CONFIG_SMP
+#define kernel_locked()		spin_is_locked(&kernel_flag)
+#elif  CONFIG_PREEMPT
+#define kernel_locked()		preempt_get_count()
+#else  /* neither */
+#define kernel_locked()		1
+#endif
+
+/*
+ * Release global kernel lock and global interrupt lock
+ */
+#define release_kernel_lock(task, cpu) \
+do { \
+	if (task->lock_depth >= 0) \
+		spin_unlock(&kernel_flag); \
+	release_irqlock(cpu); \
+	__sti(); \
+} while (0)
+
+/*
+ * Re-acquire the kernel lock
+ */
+#define reacquire_kernel_lock(task) \
+do { \
+	if (task->lock_depth >= 0) \
+		spin_lock(&kernel_flag); \
+} while (0)
+
+/*
+ * Getting the big kernel lock.
+ *
+ * This cannot happen asynchronously,
+ * so we only need to worry about other
+ * CPU's.
+ */
+static __inline__ void lock_kernel(void)
+{
+#ifdef CONFIG_PREEMPT
+	if (current->lock_depth == -1)
+		spin_lock(&kernel_flag);
+	++current->lock_depth;
 #else
-#error "We do not support SMP on SH"
-#endif /* CONFIG_SMP */
+	if (!++current->lock_depth)
+		spin_lock(&kernel_flag);
+#endif
+}
+
+static __inline__ void unlock_kernel(void)
+{
+	if (current->lock_depth < 0)
+		BUG();
+	if (--current->lock_depth < 0)
+		spin_unlock(&kernel_flag);
+}
+#endif /* CONFIG_SMP || CONFIG_PREEMPT */
 
 #endif /* __ASM_SH_SMPLOCK_H */
diff -urN linux-2.4.18/include/asm-sh/softirq.h linux/include/asm-sh/softirq.h
--- linux-2.4.18/include/asm-sh/softirq.h	Tue May  7 09:35:29 2002
+++ linux/include/asm-sh/softirq.h	Thu May 30 09:41:23 2002
@@ -6,6 +6,7 @@
 
 #define local_bh_disable()			\
 do {						\
+	preempt_disable();			\
 	local_bh_count(smp_processor_id())++;	\
 	barrier();				\
 } while (0)
@@ -14,6 +15,7 @@
 do {						\
 	barrier();				\
 	local_bh_count(smp_processor_id())--;	\
+	preempt_enable();			\
 } while (0)
 
 #define local_bh_enable()				\
@@ -23,6 +25,7 @@
 	    && softirq_pending(smp_processor_id())) {	\
 		do_softirq();				\
 	}						\
+	preempt_enable();				\
 } while (0)
 
 #define in_softirq() (local_bh_count(smp_processor_id()) != 0)
diff -urN linux-2.4.18/include/linux/brlock.h linux/include/linux/brlock.h
--- linux-2.4.18/include/linux/brlock.h	Tue May  7 09:35:22 2002
+++ linux/include/linux/brlock.h	Thu May 30 09:41:23 2002
@@ -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-2.4.18/include/linux/dcache.h linux/include/linux/dcache.h
--- linux-2.4.18/include/linux/dcache.h	Tue May  7 09:35:21 2002
+++ linux/include/linux/dcache.h	Thu May 30 09:41:23 2002
@@ -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; 
@@ -275,3 +250,34 @@
 #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-2.4.18/include/linux/fs_struct.h linux/include/linux/fs_struct.h
--- linux-2.4.18/include/linux/fs_struct.h	Tue May  7 09:35:22 2002
+++ linux/include/linux/fs_struct.h	Thu May 30 09:41:23 2002
@@ -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-2.4.18/include/linux/sched.h linux/include/linux/sched.h
--- linux-2.4.18/include/linux/sched.h	Tue May  7 09:35:21 2002
+++ linux/include/linux/sched.h	Thu May 30 09:41:23 2002
@@ -88,6 +88,7 @@
 #define TASK_UNINTERRUPTIBLE	2
 #define TASK_ZOMBIE		4
 #define TASK_STOPPED		8
+#define PREEMPT_ACTIVE		0x4000000
 
 #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 +287,7 @@
 	 * offsets of these are hardcoded elsewhere - touch with care
 	 */
 	volatile long state;	/* -1 unrunnable, 0 runnable, >0 stopped */
-	unsigned long flags;	/* per process flags, defined below */
+	int preempt_count;	/* 0 => preemptable, <0 => BUG */
 	int sigpending;
 	mm_segment_t addr_limit;	/* thread address space:
 					 	0-0xBFFFFFFF for user-thead
@@ -325,6 +329,7 @@
 	struct mm_struct *active_mm;
 	struct list_head local_pages;
 	unsigned int allocation_order, nr_local_pages;
+	unsigned long flags;
 
 /* task state */
 	struct linux_binfmt *binfmt;
@@ -927,6 +932,11 @@
 	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-2.4.18/include/linux/smp.h linux/include/linux/smp.h
--- linux-2.4.18/include/linux/smp.h	Tue May  7 09:35:22 2002
+++ linux/include/linux/smp.h	Thu May 30 09:41:23 2002
@@ -81,11 +81,17 @@
 #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; })
 #define cpu_online_map				1
 
-#endif
-#endif
+#endif /* !SMP */
+
+#define get_cpu()	smp_processor_id()
+#define put_cpu()	do { } while(0)
+
+#endif /* __LINUX_SMP_H */
diff -urN linux-2.4.18/include/linux/smp_lock.h linux/include/linux/smp_lock.h
--- linux-2.4.18/include/linux/smp_lock.h	Tue May  7 09:35:21 2002
+++ linux/include/linux/smp_lock.h	Thu May 30 09:41:23 2002
@@ -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-2.4.18/include/linux/spinlock.h linux/include/linux/spinlock.h
--- linux-2.4.18/include/linux/spinlock.h	Tue May  7 09:35:22 2002
+++ linux/include/linux/spinlock.h	Thu May 30 09:41:23 2002
@@ -2,6 +2,7 @@
 #define __LINUX_SPINLOCK_H
 
 #include <linux/config.h>
+#include <linux/compiler.h>
 
 /*
  * These are the generic versions of the spinlocks and read-write
@@ -45,8 +46,10 @@
 
 #if (DEBUG_SPINLOCKS < 1)
 
+#ifndef CONFIG_PREEMPT
 #define atomic_dec_and_lock(atomic,lock) atomic_dec_and_test(atomic)
 #define ATOMIC_DEC_AND_LOCK
+#endif
 
 /*
  * Your basic spinlocks, allowing only a single CPU anywhere
@@ -62,11 +65,11 @@
 #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)
 
@@ -125,13 +128,78 @@
 #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 preempt_get_count()	(current->preempt_count)
+#define preempt_is_disabled()	(preempt_get_count() != 0)
+
+#define preempt_disable() \
+do { \
+	++current->preempt_count; \
+	barrier(); \
+} while (0)
+
+#define preempt_enable_no_resched() \
+do { \
+	--current->preempt_count; \
+	barrier(); \
+} while (0)
+
+#define preempt_enable() \
+do { \
+	--current->preempt_count; \
+	barrier(); \
+	if (unlikely(current->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
+
+#define preempt_get_count()	(0)
+#define preempt_is_disabled()	(1)
+#define preempt_disable()	do { } while (0)
+#define preempt_enable_no_resched()	do {} while(0)
+#define preempt_enable()	do { } while (0)
+
+#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
+
 /* "lock on reference count zero" */
 #ifndef ATOMIC_DEC_AND_LOCK
 #include <asm/atomic.h>
diff -urN linux-2.4.18/include/linux/tqueue.h linux/include/linux/tqueue.h
--- linux-2.4.18/include/linux/tqueue.h	Tue May  7 09:35:21 2002
+++ linux/include/linux/tqueue.h	Thu May 30 09:41:23 2002
@@ -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-2.4.18/kernel/exit.c linux/kernel/exit.c
--- linux-2.4.18/kernel/exit.c	Tue May  7 09:35:20 2002
+++ linux/kernel/exit.c	Thu May 30 09:41:23 2002
@@ -320,8 +320,8 @@
 		/* 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);
 	}
 }
@@ -442,6 +442,11 @@
 	tsk->flags |= PF_EXITING;
 	del_timer_sync(&tsk->real_timer);
 
+	if (unlikely(preempt_get_count()))
+		printk(KERN_INFO "note: %s[%d] exited with preempt_count %d\n",
+				current->comm, current->pid,
+				preempt_get_count());
+
 fake_volatile:
 #ifdef CONFIG_BSD_PROCESS_ACCT
 	acct_process(code);
diff -urN linux-2.4.18/kernel/fork.c linux/kernel/fork.c
--- linux-2.4.18/kernel/fork.c	Tue May  7 09:35:20 2002
+++ linux/kernel/fork.c	Thu May 30 09:41:23 2002
@@ -614,6 +614,13 @@
 	if (p->binfmt && p->binfmt->module)
 		__MOD_INC_USE_COUNT(p->binfmt->module);
 
+#ifdef CONFIG_PREEMPT
+	/*
+	 * Continue with preemption disabled as part of the context
+	 * switch, so start with preempt_count set to 1.
+	 */
+	p->preempt_count = 1;
+#endif
 	p->did_exec = 0;
 	p->swappable = 0;
 	p->state = TASK_UNINTERRUPTIBLE;
diff -urN linux-2.4.18/kernel/ksyms.c linux/kernel/ksyms.c
--- linux-2.4.18/kernel/ksyms.c	Tue May  7 09:35:20 2002
+++ linux/kernel/ksyms.c	Thu May 30 09:41:23 2002
@@ -437,6 +437,9 @@
 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-2.4.18/kernel/sched.c linux/kernel/sched.c
--- linux-2.4.18/kernel/sched.c	Tue May  7 09:35:20 2002
+++ linux/kernel/sched.c	Thu May 30 09:42:08 2002
@@ -491,7 +491,7 @@
 	task_lock(prev);
 	task_release_cpu(prev);
 	mb();
-	if (prev->state == TASK_RUNNING)
+	if (task_on_runqueue(prev))
 		goto needs_resched;
 
 out_unlock:
@@ -521,7 +521,7 @@
 			goto out_unlock;
 
 		spin_lock_irqsave(&runqueue_lock, flags);
-		if ((prev->state == TASK_RUNNING) && !task_has_cpu(prev))
+		if (task_on_runqueue(prev) && !task_has_cpu(prev))
 			reschedule_idle(prev);
 		spin_unlock_irqrestore(&runqueue_lock, flags);
 		goto out_unlock;
@@ -534,6 +534,7 @@
 asmlinkage void schedule_tail(struct task_struct *prev)
 {
 	__schedule_tail(prev);
+	preempt_enable();
 }
 
 /*
@@ -553,10 +554,12 @@
 	struct list_head *tmp;
 	int this_cpu, c;
 
-
 	spin_lock_prefetch(&runqueue_lock);
 
+	preempt_disable();
+
 	if (!current->active_mm) BUG();
+
 need_resched_back:
 	prev = current;
 	this_cpu = prev->processor;
@@ -583,6 +586,14 @@
 			move_last_runqueue(prev);
 		}
 
+#ifdef CONFIG_PREEMPT
+	/*
+	 * entering from preempt_schedule, off a kernel preemption,
+	 * go straight to picking the next task.
+	 */
+	if (unlikely(preempt_get_count() & PREEMPT_ACTIVE))
+		goto treat_like_run;
+#endif
 	switch (prev->state) {
 		case TASK_INTERRUPTIBLE:
 			if (signal_pending(prev)) {
@@ -593,6 +604,9 @@
 			del_from_runqueue(prev);
 		case TASK_RUNNING:;
 	}
+#ifdef CONFIG_PREEMPT
+	treat_like_run:
+#endif
 	prev->need_resched = 0;
 
 	/*
@@ -701,9 +715,25 @@
 	reacquire_kernel_lock(current);
 	if (current->need_resched)
 		goto need_resched_back;
+	preempt_enable_no_resched();
 	return;
 }
 
+#ifdef CONFIG_PREEMPT
+/*
+ * this is is the entry point to schedule() from in-kernel preemption.
+ */
+asmlinkage void preempt_schedule(void)
+{
+	do {
+		current->preempt_count += PREEMPT_ACTIVE;
+		schedule();
+		current->preempt_count -= PREEMPT_ACTIVE;
+		barrier();
+	} while (current->need_resched);
+}
+#endif /* CONFIG_PREEMPT */
+
 /*
  * The core wakeup function.  Non-exclusive wakeups (nr_exclusive == 0) just wake everything
  * up.  If it's an exclusive wakeup (nr_exclusive == small +ve number) then we wake all the
@@ -1312,6 +1342,13 @@
 	sched_data->curr = current;
 	sched_data->last_schedule = get_cycles();
 	clear_bit(current->processor, &wait_init_idle);
+#ifdef CONFIG_PREEMPT
+	/*
+	 * fix up the preempt_count for non-CPU0 idle threads
+	 */
+	if (current->processor)
+		current->preempt_count = 0;
+#endif
 }
 
 extern void init_timervecs (void);
diff -urN linux-2.4.18/lib/dec_and_lock.c linux/lib/dec_and_lock.c
--- linux-2.4.18/lib/dec_and_lock.c	Tue May  7 09:35:21 2002
+++ linux/lib/dec_and_lock.c	Thu May 30 09:41:23 2002
@@ -1,5 +1,6 @@
 #include <linux/module.h>
 #include <linux/spinlock.h>
+#include <linux/sched.h>
 #include <asm/atomic.h>
 
 /*
diff -urN linux-2.4.18/mm/slab.c linux/mm/slab.c
--- linux-2.4.18/mm/slab.c	Tue May  7 09:35:21 2002
+++ linux/mm/slab.c	Thu May 30 09:41:23 2002
@@ -49,7 +49,8 @@
  *  constructors and destructors are called without any locking.
  *  Several members in kmem_cache_t and slab_t never change, they
  *	are accessed without any locking.
- *  The per-cpu arrays are never accessed from the wrong cpu, no locking.
+ *  The per-cpu arrays are never accessed from the wrong cpu, no locking,
+ *  	and local interrupts are disabled so slab code is preempt-safe.
  *  The non-constant members are protected with a per-cache irq spinlock.
  *
  * Further notes from the original documentation:
diff -urN linux-2.4.18/net/core/dev.c linux/net/core/dev.c
--- linux-2.4.18/net/core/dev.c	Tue May  7 09:35:32 2002
+++ linux/net/core/dev.c	Thu May 30 09:41:23 2002
@@ -1033,9 +1033,15 @@
 		int cpu = smp_processor_id();
 
 		if (dev->xmit_lock_owner != cpu) {
+			/*
+			 * The spin_lock effectivly does a preempt lock, but 
+			 * we are about to drop that...
+			 */
+			preempt_disable();
 			spin_unlock(&dev->queue_lock);
 			spin_lock(&dev->xmit_lock);
 			dev->xmit_lock_owner = cpu;
+			preempt_enable();
 
 			if (!netif_queue_stopped(dev)) {
 				if (netdev_nit)
diff -urN linux-2.4.18/net/core/skbuff.c linux/net/core/skbuff.c
--- linux-2.4.18/net/core/skbuff.c	Tue May  7 09:35:32 2002
+++ linux/net/core/skbuff.c	Thu May 30 09:41:23 2002
@@ -111,33 +111,37 @@
 
 static __inline__ struct sk_buff *skb_head_from_pool(void)
 {
-	struct sk_buff_head *list = &skb_head_pool[smp_processor_id()].list;
+	struct sk_buff_head *list;
+	struct sk_buff *skb = NULL;
+	unsigned long flags;
 
-	if (skb_queue_len(list)) {
-		struct sk_buff *skb;
-		unsigned long flags;
+	local_irq_save(flags);
 
-		local_irq_save(flags);
+	list = &skb_head_pool[smp_processor_id()].list;
+
+	if (skb_queue_len(list))
 		skb = __skb_dequeue(list);
-		local_irq_restore(flags);
-		return skb;
-	}
-	return NULL;
+
+	local_irq_restore(flags);
+	return skb;
 }
 
 static __inline__ void skb_head_to_pool(struct sk_buff *skb)
 {
-	struct sk_buff_head *list = &skb_head_pool[smp_processor_id()].list;
+	struct sk_buff_head *list;
+	unsigned long flags;
 
-	if (skb_queue_len(list) < sysctl_hot_list_len) {
-		unsigned long flags;
+	local_irq_save(flags);
+	list = &skb_head_pool[smp_processor_id()].list;
 
-		local_irq_save(flags);
+	if (skb_queue_len(list) < sysctl_hot_list_len) {
 		__skb_queue_head(list, skb);
 		local_irq_restore(flags);
 
 		return;
 	}
+
+	local_irq_restore(flags);
 	kmem_cache_free(skbuff_head_cache, skb);
 }
 
diff -urN linux-2.4.18/net/socket.c linux/net/socket.c
--- linux-2.4.18/net/socket.c	Tue May  7 09:35:31 2002
+++ linux/net/socket.c	Thu May 30 09:41:23 2002
@@ -133,7 +133,7 @@
 
 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;
 
diff -urN linux-2.4.18/net/sunrpc/pmap_clnt.c linux/net/sunrpc/pmap_clnt.c
--- linux-2.4.18/net/sunrpc/pmap_clnt.c	Tue May  7 09:35:35 2002
+++ linux/net/sunrpc/pmap_clnt.c	Thu May 30 09:41:23 2002
@@ -12,6 +12,7 @@
 #include <linux/config.h>
 #include <linux/types.h>
 #include <linux/socket.h>
+#include <linux/sched.h>
 #include <linux/kernel.h>
 #include <linux/errno.h>
 #include <linux/uio.h>