PREEMPT for ppc64

PREEMPT for ppc64

[Paul Mackerras]

Here is a patch that implements CONFIG_PREEMPT for ppc64.  Aside from
the entry.S changes to check the _TIF_NEED_RESCHED bit when returning
from an exception, most of the changes are to add preempt/{dis,en}able
in various places.  Undoubtedly I have missed some though.

This runs just fine with CONFIG_PREEMPT=y on the two pSeries machines
I tried it on, but on my dual G5 it locks up randomly.  It boots OK,
but if I do kernel compile with -j3 it doesn't get the whole way
through.  It just freezes solid with no oops.  Time for firescope
maybe.

Paul.

diff -urN linux-2.5/arch/ppc64/Kconfig test25/arch/ppc64/Kconfig
--- linux-2.5/arch/ppc64/Kconfig	2004-05-26 07:58:59.000000000 +1000
+++ test25/arch/ppc64/Kconfig	2004-06-05 20:42:42.000000000 +1000
@@ -198,7 +198,6 @@
 
 config PREEMPT
 	bool "Preemptible Kernel"
-	depends on BROKEN
 	help
 	  This option reduces the latency of the kernel when reacting to
 	  real-time or interactive events by allowing a low priority process to
diff -urN linux-2.5/arch/ppc64/kernel/align.c test25/arch/ppc64/kernel/align.c
--- linux-2.5/arch/ppc64/kernel/align.c	2004-06-01 08:11:19.000000000 +1000
+++ test25/arch/ppc64/kernel/align.c	2004-06-06 20:36:17.843892064 +1000
@@ -280,8 +280,12 @@
 	}
 
 	/* Force the fprs into the save area so we can reference them */
-	if ((flags & F) && (regs->msr & MSR_FP))
-		giveup_fpu(current);
+	if (flags & F) {
+		preempt_disable();
+		if (regs->msr & MSR_FP)
+			giveup_fpu(current);
+		preempt_enable();
+	}
 	
 	/* If we are loading, get the data from user space */
 	if (flags & LD) {
@@ -310,9 +314,11 @@
 		if (flags & F) {
 			if (nb == 4) {
 				/* Doing stfs, have to convert to single */
+				preempt_disable();
 				enable_kernel_fp();
 				cvt_df(&current->thread.fpr[reg], (float *)&data.v[4], &current->thread.fpscr);
 				disable_kernel_fp();
+				preempt_enable();
 			}
 			else
 				data.dd = current->thread.fpr[reg];
@@ -344,9 +350,11 @@
 		if (flags & F) {
 			if (nb == 4) {
 				/* Doing lfs, have to convert to double */
+				preempt_disable();
 				enable_kernel_fp();
 				cvt_fd((float *)&data.v[4], &current->thread.fpr[reg], &current->thread.fpscr);
 				disable_kernel_fp();
+				preempt_enable();
 			}
 			else
 				current->thread.fpr[reg] = data.dd;
diff -urN linux-2.5/arch/ppc64/kernel/asm-offsets.c test25/arch/ppc64/kernel/asm-offsets.c
--- linux-2.5/arch/ppc64/kernel/asm-offsets.c	2004-06-04 07:19:00.000000000 +1000
+++ test25/arch/ppc64/kernel/asm-offsets.c	2004-06-05 20:43:03.000000000 +1000
@@ -48,6 +48,7 @@
 	DEFINE(THREAD_SHIFT, THREAD_SHIFT);
 	DEFINE(THREAD_SIZE, THREAD_SIZE);
 	DEFINE(TI_FLAGS, offsetof(struct thread_info, flags));
+	DEFINE(TI_PREEMPT, offsetof(struct thread_info, preempt_count));
 
 	/* task_struct->thread */
 	DEFINE(THREAD, offsetof(struct task_struct, thread));
diff -urN linux-2.5/arch/ppc64/kernel/entry.S test25/arch/ppc64/kernel/entry.S
--- linux-2.5/arch/ppc64/kernel/entry.S	2004-05-01 12:59:54.000000000 +1000
+++ test25/arch/ppc64/kernel/entry.S	2004-06-06 18:31:22.621943960 +1000
@@ -371,15 +371,27 @@
 	andc	r9,r10,r4	/* clear MSR_EE */
 	mtmsrd	r9,1		/* Update machine state */
 
+#ifdef CONFIG_PREEMPT
+	clrrdi	r9,r1,THREAD_SHIFT	/* current_thread_info() */
+	ld	r3,_MSR(r1)
+	ld	r4,TI_FLAGS(r9)
+	andi.	r0,r3,MSR_PR
+	mtcrf	1,r4		/* get bottom 4 thread flags into cr7 */
+	bt	31-TIF_NEED_RESCHED,do_resched
+	beq	restore		/* if returning to kernel */
+	bt	31-TIF_SIGPENDING,do_user_signal
+
+#else /* !CONFIG_PREEMPT */
 	ld	r3,_MSR(r1)	/* Returning to user mode? */
 	andi.	r3,r3,MSR_PR
 	beq	restore		/* if not, just restore regs and return */
 
 	/* Check current_thread_info()->flags */
-	clrrdi	r3,r1,THREAD_SHIFT
-	ld	r3,TI_FLAGS(r3)
-	andi.	r0,r3,_TIF_USER_WORK_MASK
+	clrrdi	r9,r1,THREAD_SHIFT
+	ld	r4,TI_FLAGS(r9)
+	andi.	r0,r4,_TIF_USER_WORK_MASK
 	bne	do_work
+#endif
 
 	addi	r0,r1,INT_FRAME_SIZE	/* size of frame */
 	ld	r4,PACACURRENT(r13)
@@ -452,18 +464,47 @@
 
 	rfid
 
+#ifndef CONFIG_PREEMPT
 /* Note: this must change if we start using the  TIF_NOTIFY_RESUME bit */
 do_work:
-	/* Enable interrupts */
-	mtmsrd	r10,1
+	andi.	r0,r4,_TIF_NEED_RESCHED
+	beq	do_user_signal
+
+#else /* CONFIG_PREEMPT */
+do_resched:
+	bne	do_user_resched		/* if returning to user mode */
+	/* Check that preempt_count() == 0 and interrupts are enabled */
+	lwz	r8,TI_PREEMPT(r9)
+	cmpwi	cr1,r8,0
+#ifdef CONFIG_PPC_ISERIES
+	ld	r0,SOFTE(r1)
+	cmpdi	r0,0
+#else
+	andi.	r0,r3,MSR_EE
+#endif
+	crandc	eq,cr1*4+eq,eq
+	bne	restore
+	/* here we are preempting the current task */
+1:	lis	r0,PREEMPT_ACTIVE@h
+	stw	r0,TI_PREEMPT(r9)
+#ifdef CONFIG_PPC_ISERIES
+	li	r0,1
+	stb	r0,PACAPROCENABLED(r13)
+#endif
+#endif /* CONFIG_PREEMPT */
 
-	andi.	r0,r3,_TIF_NEED_RESCHED
-	beq	1f
+do_user_resched:
+	mtmsrd	r10,1		/* reenable interrupts */
 	bl	.schedule
+#ifdef CONFIG_PREEMPT
+	clrrdi	r9,r1,THREAD_SHIFT
+	li	r0,0
+	stw	r0,TI_PREEMPT(r9)
+#endif
 	b	.ret_from_except
 
-1:	andi.	r0,r3,_TIF_SIGPENDING
-	beq	.ret_from_except
+do_user_signal:
+	mtmsrd	r10,1
 	li	r3,0
 	addi	r4,r1,STACK_FRAME_OVERHEAD
 	bl	.do_signal
diff -urN linux-2.5/arch/ppc64/kernel/process.c test25/arch/ppc64/kernel/process.c
--- linux-2.5/arch/ppc64/kernel/process.c	2004-06-01 08:11:19.000000000 +1000
+++ test25/arch/ppc64/kernel/process.c	2004-06-06 20:39:54.240879144 +1000
@@ -67,6 +67,8 @@
 
 void enable_kernel_fp(void)
 {
+	WARN_ON(preemptible());
+
 #ifdef CONFIG_SMP
 	if (current->thread.regs && (current->thread.regs->msr & MSR_FP))
 		giveup_fpu(current);
@@ -84,8 +86,10 @@
 
 	if (!regs)
 		return 0;
+	preempt_disable();
 	if (tsk == current && (regs->msr & MSR_FP))
 		giveup_fpu(current);
+	preempt_enable();
 
 	memcpy(fpregs, &tsk->thread.fpr[0], sizeof(*fpregs));
 
@@ -96,6 +100,8 @@
 
 void enable_kernel_altivec(void)
 {
+	WARN_ON(preemptible());
+
 #ifdef CONFIG_SMP
 	if (current->thread.regs && (current->thread.regs->msr & MSR_VEC))
 		giveup_altivec(current);
@@ -109,8 +115,10 @@
 
 int dump_task_altivec(struct pt_regs *regs, elf_vrregset_t *vrregs)
 {
+	preempt_disable();
 	if (regs->msr & MSR_VEC)
 		giveup_altivec(current);
+	preempt_enable();
 	memcpy(vrregs, &current->thread.vr[0], sizeof(*vrregs));
 	return 1;
 }
@@ -249,12 +257,14 @@
 
 	if (regs == NULL)
 		return;
+	preempt_disable();
 	if (regs->msr & MSR_FP)
 		giveup_fpu(current);
 #ifdef CONFIG_ALTIVEC
 	if (regs->msr & MSR_VEC)
 		giveup_altivec(current);
 #endif /* CONFIG_ALTIVEC */
+	preempt_enable();
 }
 
 /*
@@ -439,12 +449,14 @@
 	error = PTR_ERR(filename);
 	if (IS_ERR(filename))
 		goto out;
+	preempt_disable();
 	if (regs->msr & MSR_FP)
 		giveup_fpu(current);
 #ifdef CONFIG_ALTIVEC
 	if (regs->msr & MSR_VEC)
 		giveup_altivec(current);
 #endif /* CONFIG_ALTIVEC */
+	preempt_enable();
 	error = do_execve(filename, (char __user * __user *) a1,
 				    (char __user * __user *) a2, regs);
   
diff -urN linux-2.5/arch/ppc64/kernel/ptrace.c test25/arch/ppc64/kernel/ptrace.c
--- linux-2.5/arch/ppc64/kernel/ptrace.c	2004-06-01 08:11:19.000000000 +1000
+++ test25/arch/ppc64/kernel/ptrace.c	2004-06-05 20:55:21.000000000 +1000
@@ -50,6 +50,32 @@
 	clear_single_step(child);
 }
 
+/* Make sure child's FP registers aren't cached in CPU registers. */
+#ifdef CONFIG_SMP
+/*
+ * On SMP we save away the FP register state on context switch.
+ * Since the child is stopped, there is something seriously wrong
+ * if its FP state appears to still be in the CPU registers.
+ */
+void ptrace_flush_child_fp(struct task_struct *child)
+{
+	BUG_ON(child->thread.regs && (child->thread.regs->msr & MSR_FP));
+}
+#else
+/*
+ * On UP the child's register state may still be in the CPU registers.
+ * We need to disable preemption so that once we decide we need to save
+ * the registers away, we save all of them without getting switched.
+ */
+void ptrace_flush_child_fp(struct task_struct *child)
+{
+	preempt_disable();
+	if (child->thread.regs->msr & MSR_FP)
+		giveup_fpu(child);
+	preempt_enable();
+}
+#endif
+
 int sys_ptrace(long request, long pid, long addr, long data)
 {
 	struct task_struct *child;
@@ -119,8 +145,7 @@
 		if (index < PT_FPR0) {
 			tmp = get_reg(child, (int)index);
 		} else {
-			if (child->thread.regs->msr & MSR_FP)
-				giveup_fpu(child);
+			ptrace_flush_child_fp(child);
 			tmp = ((unsigned long *)child->thread.fpr)[index - PT_FPR0];
 		}
 		ret = put_user(tmp,(unsigned long __user *) data);
@@ -152,8 +177,7 @@
 		if (index < PT_FPR0) {
 			ret = put_reg(child, index, data);
 		} else {
-			if (child->thread.regs->msr & MSR_FP)
-				giveup_fpu(child);
+			ptrace_flush_child_fp(child);
 			((unsigned long *)child->thread.fpr)[index - PT_FPR0] = data;
 			ret = 0;
 		}
@@ -245,8 +269,7 @@
 		unsigned long *reg = &((unsigned long *)child->thread.fpr)[0];
 		unsigned long __user *tmp = (unsigned long __user *)addr;
 
-		if (child->thread.regs->msr & MSR_FP)
-			giveup_fpu(child);
+		ptrace_flush_child_fp(child);
 
 		for (i = 0; i < 32; i++) {
 			ret = put_user(*reg, tmp);
@@ -263,8 +286,7 @@
 		unsigned long *reg = &((unsigned long *)child->thread.fpr)[0];
 		unsigned long __user *tmp = (unsigned long __user *)addr;
 
-		if (child->thread.regs->msr & MSR_FP)
-			giveup_fpu(child);
+		ptrace_flush_child_fp(child);
 
 		for (i = 0; i < 32; i++) {
 			ret = get_user(*reg, tmp);
diff -urN linux-2.5/arch/ppc64/kernel/ptrace32.c test25/arch/ppc64/kernel/ptrace32.c
--- linux-2.5/arch/ppc64/kernel/ptrace32.c	2004-06-01 08:11:19.000000000 +1000
+++ test25/arch/ppc64/kernel/ptrace32.c	2004-06-05 20:54:30.000000000 +1000
@@ -136,8 +136,7 @@
 		if (index < PT_FPR0) {
 			tmp = get_reg(child, index);
 		} else {
-			if (child->thread.regs->msr & MSR_FP)
-				giveup_fpu(child);
+			ptrace_flush_child_fp(child);
 			/*
 			 * the user space code considers the floating point
 			 * to be an array of unsigned int (32 bits) - the
@@ -179,8 +178,7 @@
 			break;
 
 		if (numReg >= PT_FPR0) {
-			if (child->thread.regs->msr & MSR_FP)
-				giveup_fpu(child);
+			ptrace_flush_child_fp(child);
 			tmp = ((unsigned long int *)child->thread.fpr)[numReg - PT_FPR0];
 		} else { /* register within PT_REGS struct */
 			tmp = get_reg(child, numReg);
@@ -244,8 +242,7 @@
 		if (index < PT_FPR0) {
 			ret = put_reg(child, index, data);
 		} else {
-			if (child->thread.regs->msr & MSR_FP)
-				giveup_fpu(child);
+			ptrace_flush_child_fp(child);
 			/*
 			 * the user space code considers the floating point
 			 * to be an array of unsigned int (32 bits) - the
@@ -283,8 +280,7 @@
 				|| ((numReg > PT_CCR) && (numReg < PT_FPR0)))
 			break;
 		if (numReg >= PT_FPR0) {
-			if (child->thread.regs->msr & MSR_FP)
-				giveup_fpu(child);
+			ptrace_flush_child_fp(child);
 		}
 		if (numReg == PT_MSR)
 			data = (data & MSR_DEBUGCHANGE)
@@ -379,8 +375,7 @@
 		unsigned long *reg = &((unsigned long *)child->thread.fpr)[0];
 		unsigned int __user *tmp = (unsigned int __user *)addr;
 
-		if (child->thread.regs->msr & MSR_FP)
-			giveup_fpu(child);
+		ptrace_flush_child_fp(child);
 
 		for (i = 0; i < 32; i++) {
 			ret = put_user(*reg, tmp);
@@ -397,8 +392,7 @@
 		unsigned long *reg = &((unsigned long *)child->thread.fpr)[0];
 		unsigned int __user *tmp = (unsigned int __user *)addr;
 
-		if (child->thread.regs->msr & MSR_FP)
-			giveup_fpu(child);
+		ptrace_flush_child_fp(child);
 
 		for (i = 0; i < 32; i++) {
 			ret = get_user(*reg, tmp);
diff -urN linux-2.5/arch/ppc64/kernel/signal.c test25/arch/ppc64/kernel/signal.c
--- linux-2.5/arch/ppc64/kernel/signal.c	2004-06-01 08:11:19.000000000 +1000
+++ test25/arch/ppc64/kernel/signal.c	2004-06-05 21:20:35.000000000 +1000
@@ -131,8 +131,10 @@
 #endif
 	long err = 0;
 
+	preempt_disable();
 	if (regs->msr & MSR_FP)
 		giveup_fpu(current);
+	preempt_enable();
 
 	/* Make sure signal doesn't get spurrious FP exceptions */
 	current->thread.fpscr = 0;
@@ -142,8 +144,10 @@
 
 	/* save altivec registers */
 	if (current->thread.used_vr) {		
+		preempt_disable();
 		if (regs->msr & MSR_VEC)
 			giveup_altivec(current);
+		preempt_enable();
 		/* Copy 33 vec registers (vr0..31 and vscr) to the stack */
 		err |= __copy_to_user(v_regs, current->thread.vr, 33 * sizeof(vector128));
 		/* set MSR_VEC in the MSR value in the frame to indicate that sc->v_reg)
diff -urN linux-2.5/arch/ppc64/kernel/signal32.c test25/arch/ppc64/kernel/signal32.c
--- linux-2.5/arch/ppc64/kernel/signal32.c	2004-06-01 08:11:19.000000000 +1000
+++ test25/arch/ppc64/kernel/signal32.c	2004-06-05 21:20:52.000000000 +1000
@@ -132,9 +132,11 @@
 	int i, err = 0;
 	
 	/* Make sure floating point registers are stored in regs */ 
+	preempt_disable();
 	if (regs->msr & MSR_FP)
 		giveup_fpu(current);
-	
+	preempt_enable();
+
 	/* save general and floating-point registers */
 	for (i = 0; i <= PT_RESULT; i ++)
 		err |= __put_user((unsigned int)gregs[i], &frame->mc_gregs[i]);
@@ -148,8 +150,10 @@
 #ifdef CONFIG_ALTIVEC
 	/* save altivec registers */
 	if (current->thread.used_vr) {
+		preempt_disable();
 		if (regs->msr & MSR_VEC)
 			giveup_altivec(current);
+		preempt_enable();
 		if (__copy_to_user(&frame->mc_vregs, current->thread.vr,
 				   ELF_NVRREG32 * sizeof(vector128)))
 			return 1;
diff -urN linux-2.5/arch/ppc64/kernel/sys_ppc32.c test25/arch/ppc64/kernel/sys_ppc32.c
--- linux-2.5/arch/ppc64/kernel/sys_ppc32.c	2004-06-01 08:11:19.000000000 +1000
+++ test25/arch/ppc64/kernel/sys_ppc32.c	2004-06-04 22:48:11.000000000 +1000
@@ -617,12 +617,14 @@
 	error = PTR_ERR(filename);
 	if (IS_ERR(filename))
 		goto out;
+	preempt_disable();
 	if (regs->msr & MSR_FP)
 		giveup_fpu(current);
 #ifdef CONFIG_ALTIVEC
 	if (regs->msr & MSR_VEC)
 		giveup_altivec(current);
 #endif /* CONFIG_ALTIVEC */
+	preempt_enable();
 
 	error = compat_do_execve(filename, compat_ptr(a1), compat_ptr(a2), regs);
 
diff -urN linux-2.5/arch/ppc64/kernel/traps.c test25/arch/ppc64/kernel/traps.c
--- linux-2.5/arch/ppc64/kernel/traps.c	2004-05-22 09:08:53.000000000 +1000
+++ test25/arch/ppc64/kernel/traps.c	2004-06-05 21:21:48.000000000 +1000
@@ -308,8 +308,10 @@
 	siginfo_t info;
 	unsigned long fpscr;
 
+	preempt_disable();
 	if (regs->msr & MSR_FP)
 		giveup_fpu(current);
+	preempt_enable();
 
 	fpscr = current->thread.fpscr;
 
@@ -521,8 +523,10 @@
 void
 AltivecAssistException(struct pt_regs *regs)
 {
+	preempt_disable();
 	if (regs->msr & MSR_VEC)
 		giveup_altivec(current);
+	preempt_enable();
 	/* XXX quick hack for now: set the non-Java bit in the VSCR */
 	current->thread.vscr.u[3] |= 0x10000;
 }
diff -urN linux-2.5/include/asm-ppc64/hardirq.h test25/include/asm-ppc64/hardirq.h
--- linux-2.5/include/asm-ppc64/hardirq.h	2003-10-17 06:01:35.000000000 +1000
+++ test25/include/asm-ppc64/hardirq.h	2004-06-06 20:37:24.854954688 +1000
@@ -82,9 +82,11 @@
 
 #ifdef CONFIG_PREEMPT
 # define in_atomic()	((preempt_count() & ~PREEMPT_ACTIVE) != kernel_locked())
+# define preemptible()	(preempt_count() == 0 && !irqs_disabled())
 # define IRQ_EXIT_OFFSET (HARDIRQ_OFFSET-1)
 #else
 # define in_atomic()	(preempt_count() != 0)
+# define preemptible()	0
 # define IRQ_EXIT_OFFSET HARDIRQ_OFFSET
 #endif
 #define irq_exit()							\
diff -urN linux-2.5/include/asm-ppc64/ptrace.h test25/include/asm-ppc64/ptrace.h
--- linux-2.5/include/asm-ppc64/ptrace.h	2004-05-20 08:06:38.000000000 +1000
+++ test25/include/asm-ppc64/ptrace.h	2004-06-05 21:22:35.000000000 +1000
@@ -60,6 +60,9 @@
 	PPC_REG_32 result; 	/* Result of a system call */
 };
 
+struct task_struct;
+extern void ptrace_flush_child_fp(struct task_struct *);
+
 #endif
 
 #define STACK_FRAME_OVERHEAD	112	/* size of minimum stack frame */
diff -urN linux-2.5/include/asm-ppc64/thread_info.h test25/include/asm-ppc64/thread_info.h
--- linux-2.5/include/asm-ppc64/thread_info.h	2004-05-26 18:14:47.000000000 +1000
+++ test25/include/asm-ppc64/thread_info.h	2004-06-06 18:23:21.819942200 +1000
@@ -13,6 +13,7 @@
 #ifndef __ASSEMBLY__
 #include <linux/config.h>
 #include <asm/processor.h>
+#include <asm/page.h>
 #include <linux/stringify.h>
 
 /*
@@ -23,7 +24,7 @@
 	struct exec_domain *exec_domain;	/* execution domain */
 	unsigned long	flags;			/* low level flags */
 	int		cpu;			/* cpu we're on */
-	int		preempt_count;		/* not used at present */
+	int		preempt_count;
 	struct restart_block restart_block;
 };
 
@@ -73,7 +74,7 @@
 static inline struct thread_info *current_thread_info(void)
 {
 	struct thread_info *ti;
-	__asm__("clrrdi %0,1,14" : "=r"(ti));
+	__asm__("clrrdi %0,1,%1" : "=r"(ti) : "i" (THREAD_SHIFT));
 	return ti;
 }
 
@@ -83,6 +84,8 @@
 
 /*
  * thread information flag bit numbers
+ * N.B. If TIF_SIGPENDING or TIF_NEED_RESCHED are changed
+ * to be >= 4, code in entry.S will need to be changed.
  */
 #define TIF_SYSCALL_TRACE	0	/* syscall trace active */
 #define TIF_NOTIFY_RESUME	1	/* resumption notification requested */

Re: PREEMPT for ppc64

[Linus Torvalds]

On Mon, 7 Jun 2004, Paul Mackerras wrote:
>
> Here is a patch that implements CONFIG_PREEMPT for ppc64.  Aside from
> the entry.S changes to check the _TIF_NEED_RESCHED bit when returning
> from an exception, most of the changes are to add preempt/{dis,en}able
> in various places.  Undoubtedly I have missed some though.

I would really suggest you push these into the "enable_kernel_fp()" thing, 
for example, rather than open-coding them. Also, code like

	+     preempt_disable();
	      if (regs->msr & MSR_VEC)
	              giveup_altivec(current);
	+     preempt_enable();

doesn't seem to make much sense, since "regs->msr" certainly isn't 
changing, so clearly the above is equivalent to just pushing the whole 
preempt disable into "giveup_altivec()".

The most _common_ bug (and the one I don't see any code for at all in your
patch) is stuff that knows which CPU it is on, or that reads actual
special CPU registers and acts on them. The other thing to look out for is
anything that gets the CPU number: use "get_cpu() + put_cpu()" rather than
"smp_processor_id()".

		Linus

Re: PREEMPT for ppc64

[Benjamin Herrenschmidt]

> doesn't seem to make much sense, since "regs->msr" certainly isn't
> changing, so clearly the above is equivalent to just pushing the whole
> preempt disable into "giveup_altivec()".

regs->msr can be changing. If you preempt between those 2 lines,
another process can steal the altivec or FP unit and your "regs"
wille be affected.

> The most _common_ bug (and the one I don't see any code for at all in your
> patch) is stuff that knows which CPU it is on, or that reads actual
> special CPU registers and acts on them. The other thing to look out for is
> anything that gets the CPU number: use "get_cpu() + put_cpu()" rather than
> "smp_processor_id()".
> 
> 		Linus
> 
> ** Sent via the linuxppc64-dev mail list. See http://lists.linuxppc.org/
-- 
Benjamin Herrenschmidt <benh@kernel.crashing.org>

Re: PREEMPT for ppc64

[Paul Mackerras]

Linus Torvalds writes:

> The most _common_ bug (and the one I don't see any code for at all in your
> patch) is stuff that knows which CPU it is on, or that reads actual
> special CPU registers and acts on them. The other thing to look out for is
> anything that gets the CPU number: use "get_cpu() + put_cpu()" rather than
> "smp_processor_id()".

I went through and looked at all the uses of smp_processor_id(),
get_paca(), mfspr(), and mtspr().  There were a few places in
arch/ppc64/mm/*.c that were using smp_processor_id() to do the
optimization of using the local-processor-only form of the tlb
invalidate instruction.  I changed them to use get_cpu/put_cpu and
that has fixed the problem.  It's running well now, I have been using
it on a G5 and other boxes and it hasn't hung or crashed.

I also made flush_fp_to_thread() and flush_altivec_to_thread()
functions.  It is necessary to disable preemption before testing
regs->msr (as Ben noted) so I put in a comment about that.

Here's the current patch.  I think it should go in after 2.6.7 is out.

Regards,
Paul.

diff -urN linux-2.5/arch/ppc64/Kconfig test25/arch/ppc64/Kconfig
--- linux-2.5/arch/ppc64/Kconfig	2004-05-26 07:58:59.000000000 +1000
+++ test25/arch/ppc64/Kconfig	2004-06-05 20:42:42.000000000 +1000
@@ -198,7 +198,6 @@
 
 config PREEMPT
 	bool "Preemptible Kernel"
-	depends on BROKEN
 	help
 	  This option reduces the latency of the kernel when reacting to
 	  real-time or interactive events by allowing a low priority process to
diff -urN linux-2.5/arch/ppc64/kernel/align.c test25/arch/ppc64/kernel/align.c
--- linux-2.5/arch/ppc64/kernel/align.c	2004-06-01 08:11:19.000000000 +1000
+++ test25/arch/ppc64/kernel/align.c	2004-06-08 15:37:40.000000000 +1000
@@ -22,8 +22,6 @@
 #include <asm/cache.h>
 #include <asm/cputable.h>
 
-void disable_kernel_fp(void); /* asm function from head.S */
-
 struct aligninfo {
 	unsigned char len;
 	unsigned char flags;
@@ -280,8 +278,11 @@
 	}
 
 	/* Force the fprs into the save area so we can reference them */
-	if ((flags & F) && (regs->msr & MSR_FP))
-		giveup_fpu(current);
+	if (flags & F) {
+		if (!user_mode(regs))
+			return 0;
+		flush_fp_to_thread(current);
+	}
 	
 	/* If we are loading, get the data from user space */
 	if (flags & LD) {
@@ -310,9 +311,11 @@
 		if (flags & F) {
 			if (nb == 4) {
 				/* Doing stfs, have to convert to single */
+				preempt_disable();
 				enable_kernel_fp();
 				cvt_df(&current->thread.fpr[reg], (float *)&data.v[4], &current->thread.fpscr);
 				disable_kernel_fp();
+				preempt_enable();
 			}
 			else
 				data.dd = current->thread.fpr[reg];
@@ -344,9 +347,11 @@
 		if (flags & F) {
 			if (nb == 4) {
 				/* Doing lfs, have to convert to double */
+				preempt_disable();
 				enable_kernel_fp();
 				cvt_fd((float *)&data.v[4], &current->thread.fpr[reg], &current->thread.fpscr);
 				disable_kernel_fp();
+				preempt_enable();
 			}
 			else
 				current->thread.fpr[reg] = data.dd;
diff -urN linux-2.5/arch/ppc64/kernel/asm-offsets.c test25/arch/ppc64/kernel/asm-offsets.c
--- linux-2.5/arch/ppc64/kernel/asm-offsets.c	2004-06-04 07:19:00.000000000 +1000
+++ test25/arch/ppc64/kernel/asm-offsets.c	2004-06-05 20:43:03.000000000 +1000
@@ -48,6 +48,7 @@
 	DEFINE(THREAD_SHIFT, THREAD_SHIFT);
 	DEFINE(THREAD_SIZE, THREAD_SIZE);
 	DEFINE(TI_FLAGS, offsetof(struct thread_info, flags));
+	DEFINE(TI_PREEMPT, offsetof(struct thread_info, preempt_count));
 
 	/* task_struct->thread */
 	DEFINE(THREAD, offsetof(struct task_struct, thread));
diff -urN linux-2.5/arch/ppc64/kernel/entry.S test25/arch/ppc64/kernel/entry.S
--- linux-2.5/arch/ppc64/kernel/entry.S	2004-05-01 12:59:54.000000000 +1000
+++ test25/arch/ppc64/kernel/entry.S	2004-06-06 18:31:22.000000000 +1000
@@ -371,15 +371,27 @@
 	andc	r9,r10,r4	/* clear MSR_EE */
 	mtmsrd	r9,1		/* Update machine state */
 
+#ifdef CONFIG_PREEMPT
+	clrrdi	r9,r1,THREAD_SHIFT	/* current_thread_info() */
+	ld	r3,_MSR(r1)
+	ld	r4,TI_FLAGS(r9)
+	andi.	r0,r3,MSR_PR
+	mtcrf	1,r4		/* get bottom 4 thread flags into cr7 */
+	bt	31-TIF_NEED_RESCHED,do_resched
+	beq	restore		/* if returning to kernel */
+	bt	31-TIF_SIGPENDING,do_user_signal
+
+#else /* !CONFIG_PREEMPT */
 	ld	r3,_MSR(r1)	/* Returning to user mode? */
 	andi.	r3,r3,MSR_PR
 	beq	restore		/* if not, just restore regs and return */
 
 	/* Check current_thread_info()->flags */
-	clrrdi	r3,r1,THREAD_SHIFT
-	ld	r3,TI_FLAGS(r3)
-	andi.	r0,r3,_TIF_USER_WORK_MASK
+	clrrdi	r9,r1,THREAD_SHIFT
+	ld	r4,TI_FLAGS(r9)
+	andi.	r0,r4,_TIF_USER_WORK_MASK
 	bne	do_work
+#endif
 
 	addi	r0,r1,INT_FRAME_SIZE	/* size of frame */
 	ld	r4,PACACURRENT(r13)
@@ -452,18 +464,47 @@
 
 	rfid
 
+#ifndef CONFIG_PREEMPT
 /* Note: this must change if we start using the  TIF_NOTIFY_RESUME bit */
 do_work:
-	/* Enable interrupts */
-	mtmsrd	r10,1
+	andi.	r0,r4,_TIF_NEED_RESCHED
+	beq	do_user_signal
+
+#else /* CONFIG_PREEMPT */
+do_resched:
+	bne	do_user_resched		/* if returning to user mode */
+	/* Check that preempt_count() == 0 and interrupts are enabled */
+	lwz	r8,TI_PREEMPT(r9)
+	cmpwi	cr1,r8,0
+#ifdef CONFIG_PPC_ISERIES
+	ld	r0,SOFTE(r1)
+	cmpdi	r0,0
+#else
+	andi.	r0,r3,MSR_EE
+#endif
+	crandc	eq,cr1*4+eq,eq
+	bne	restore
+	/* here we are preempting the current task */
+1:	lis	r0,PREEMPT_ACTIVE@h
+	stw	r0,TI_PREEMPT(r9)
+#ifdef CONFIG_PPC_ISERIES
+	li	r0,1
+	stb	r0,PACAPROCENABLED(r13)
+#endif
+#endif /* CONFIG_PREEMPT */
 
-	andi.	r0,r3,_TIF_NEED_RESCHED
-	beq	1f
+do_user_resched:
+	mtmsrd	r10,1		/* reenable interrupts */
 	bl	.schedule
+#ifdef CONFIG_PREEMPT
+	clrrdi	r9,r1,THREAD_SHIFT
+	li	r0,0
+	stw	r0,TI_PREEMPT(r9)
+#endif
 	b	.ret_from_except
 
-1:	andi.	r0,r3,_TIF_SIGPENDING
-	beq	.ret_from_except
+do_user_signal:
+	mtmsrd	r10,1
 	li	r3,0
 	addi	r4,r1,STACK_FRAME_OVERHEAD
 	bl	.do_signal
diff -urN linux-2.5/arch/ppc64/kernel/process.c test25/arch/ppc64/kernel/process.c
--- linux-2.5/arch/ppc64/kernel/process.c	2004-06-01 08:11:19.000000000 +1000
+++ test25/arch/ppc64/kernel/process.c	2004-06-08 16:23:02.968947112 +1000
@@ -65,8 +65,43 @@
 	.page_table_lock = SPIN_LOCK_UNLOCKED,
 };
 
+/*
+ * Make sure the floating-point register state in the
+ * the thread_struct is up to date for task tsk.
+ */
+void flush_fp_to_thread(struct task_struct *tsk)
+{
+	if (tsk->thread.regs) {
+		/*
+		 * We need to disable preemption here because if we didn't,
+		 * another process could get scheduled after the regs->msr
+		 * test but before we have finished saving the FP registers
+		 * to the thread_struct.  That process could take over the
+		 * FPU, and then when we get scheduled again we would store
+		 * bogus values for the remaining FP registers.
+		 */
+		preempt_disable();
+		if (tsk->thread.regs->msr & MSR_FP) {
+#ifdef CONFIG_SMP
+			/*
+			 * This should only ever be called for current or
+			 * for a stopped child process.  Since we save away
+			 * the FP register state on context switch on SMP,
+			 * there is something wrong if a stopped child appears
+			 * to still have its FP state in the CPU registers.
+			 */
+			BUG_ON(tsk != current);
+#endif
+			giveup_fpu(current);
+		}
+		preempt_enable();
+	}
+}
+
 void enable_kernel_fp(void)
 {
+	WARN_ON(preemptible());
+
 #ifdef CONFIG_SMP
 	if (current->thread.regs && (current->thread.regs->msr & MSR_FP))
 		giveup_fpu(current);
@@ -80,12 +115,9 @@
 
 int dump_task_fpu(struct task_struct *tsk, elf_fpregset_t *fpregs)
 {
-	struct pt_regs *regs = tsk->thread.regs;
-
-	if (!regs)
+	if (!tsk->thread.regs)
 		return 0;
-	if (tsk == current && (regs->msr & MSR_FP))
-		giveup_fpu(current);
+	flush_fp_to_thread(current);
 
 	memcpy(fpregs, &tsk->thread.fpr[0], sizeof(*fpregs));
 
@@ -96,6 +128,8 @@
 
 void enable_kernel_altivec(void)
 {
+	WARN_ON(preemptible());
+
 #ifdef CONFIG_SMP
 	if (current->thread.regs && (current->thread.regs->msr & MSR_VEC))
 		giveup_altivec(current);
@@ -107,10 +141,29 @@
 }
 EXPORT_SYMBOL(enable_kernel_altivec);
 
+/*
+ * Make sure the VMX/Altivec register state in the
+ * the thread_struct is up to date for task tsk.
+ */
+void flush_altivec_to_thread(struct task_struct *tsk)
+{
+#ifdef CONFIG_ALTIVEC
+	if (tsk->thread.regs) {
+		preempt_disable();
+		if (tsk->thread.regs->msr & MSR_VEC) {
+#ifdef CONFIG_SMP
+			BUG_ON(tsk != current);
+#endif
+			giveup_altivec(current);
+		}
+		preempt_enable();
+	}
+#endif
+}
+
 int dump_task_altivec(struct pt_regs *regs, elf_vrregset_t *vrregs)
 {
-	if (regs->msr & MSR_VEC)
-		giveup_altivec(current);
+	flush_altivec_to_thread(current);
 	memcpy(vrregs, &current->thread.vr[0], sizeof(*vrregs));
 	return 1;
 }
@@ -245,16 +298,8 @@
  */
 void prepare_to_copy(struct task_struct *tsk)
 {
-	struct pt_regs *regs = tsk->thread.regs;
-
-	if (regs == NULL)
-		return;
-	if (regs->msr & MSR_FP)
-		giveup_fpu(current);
-#ifdef CONFIG_ALTIVEC
-	if (regs->msr & MSR_VEC)
-		giveup_altivec(current);
-#endif /* CONFIG_ALTIVEC */
+	flush_fp_to_thread(current);
+	flush_altivec_to_thread(current);
 }
 
 /*
@@ -439,12 +484,8 @@
 	error = PTR_ERR(filename);
 	if (IS_ERR(filename))
 		goto out;
-	if (regs->msr & MSR_FP)
-		giveup_fpu(current);
-#ifdef CONFIG_ALTIVEC
-	if (regs->msr & MSR_VEC)
-		giveup_altivec(current);
-#endif /* CONFIG_ALTIVEC */
+	flush_fp_to_thread(current);
+	flush_altivec_to_thread(current);
 	error = do_execve(filename, (char __user * __user *) a1,
 				    (char __user * __user *) a2, regs);
   
diff -urN linux-2.5/arch/ppc64/kernel/ptrace.c test25/arch/ppc64/kernel/ptrace.c
--- linux-2.5/arch/ppc64/kernel/ptrace.c	2004-06-01 08:11:19.000000000 +1000
+++ test25/arch/ppc64/kernel/ptrace.c	2004-06-08 14:20:46.000000000 +1000
@@ -119,8 +119,7 @@
 		if (index < PT_FPR0) {
 			tmp = get_reg(child, (int)index);
 		} else {
-			if (child->thread.regs->msr & MSR_FP)
-				giveup_fpu(child);
+			flush_fp_to_thread(child);
 			tmp = ((unsigned long *)child->thread.fpr)[index - PT_FPR0];
 		}
 		ret = put_user(tmp,(unsigned long __user *) data);
@@ -152,8 +151,7 @@
 		if (index < PT_FPR0) {
 			ret = put_reg(child, index, data);
 		} else {
-			if (child->thread.regs->msr & MSR_FP)
-				giveup_fpu(child);
+			flush_fp_to_thread(child);
 			((unsigned long *)child->thread.fpr)[index - PT_FPR0] = data;
 			ret = 0;
 		}
@@ -245,8 +243,7 @@
 		unsigned long *reg = &((unsigned long *)child->thread.fpr)[0];
 		unsigned long __user *tmp = (unsigned long __user *)addr;
 
-		if (child->thread.regs->msr & MSR_FP)
-			giveup_fpu(child);
+		flush_fp_to_thread(child);
 
 		for (i = 0; i < 32; i++) {
 			ret = put_user(*reg, tmp);
@@ -263,8 +260,7 @@
 		unsigned long *reg = &((unsigned long *)child->thread.fpr)[0];
 		unsigned long __user *tmp = (unsigned long __user *)addr;
 
-		if (child->thread.regs->msr & MSR_FP)
-			giveup_fpu(child);
+		flush_fp_to_thread(child);
 
 		for (i = 0; i < 32; i++) {
 			ret = get_user(*reg, tmp);
diff -urN linux-2.5/arch/ppc64/kernel/ptrace32.c test25/arch/ppc64/kernel/ptrace32.c
--- linux-2.5/arch/ppc64/kernel/ptrace32.c	2004-06-01 08:11:19.000000000 +1000
+++ test25/arch/ppc64/kernel/ptrace32.c	2004-06-08 14:35:01.000000000 +1000
@@ -136,8 +136,7 @@
 		if (index < PT_FPR0) {
 			tmp = get_reg(child, index);
 		} else {
-			if (child->thread.regs->msr & MSR_FP)
-				giveup_fpu(child);
+			flush_fp_to_thread(child);
 			/*
 			 * the user space code considers the floating point
 			 * to be an array of unsigned int (32 bits) - the
@@ -179,8 +178,7 @@
 			break;
 
 		if (numReg >= PT_FPR0) {
-			if (child->thread.regs->msr & MSR_FP)
-				giveup_fpu(child);
+			flush_fp_to_thread(child);
 			tmp = ((unsigned long int *)child->thread.fpr)[numReg - PT_FPR0];
 		} else { /* register within PT_REGS struct */
 			tmp = get_reg(child, numReg);
@@ -244,8 +242,7 @@
 		if (index < PT_FPR0) {
 			ret = put_reg(child, index, data);
 		} else {
-			if (child->thread.regs->msr & MSR_FP)
-				giveup_fpu(child);
+			flush_fp_to_thread(child);
 			/*
 			 * the user space code considers the floating point
 			 * to be an array of unsigned int (32 bits) - the
@@ -283,8 +280,7 @@
 				|| ((numReg > PT_CCR) && (numReg < PT_FPR0)))
 			break;
 		if (numReg >= PT_FPR0) {
-			if (child->thread.regs->msr & MSR_FP)
-				giveup_fpu(child);
+			flush_fp_to_thread(child);
 		}
 		if (numReg == PT_MSR)
 			data = (data & MSR_DEBUGCHANGE)
@@ -379,8 +375,7 @@
 		unsigned long *reg = &((unsigned long *)child->thread.fpr)[0];
 		unsigned int __user *tmp = (unsigned int __user *)addr;
 
-		if (child->thread.regs->msr & MSR_FP)
-			giveup_fpu(child);
+		flush_fp_to_thread(child);
 
 		for (i = 0; i < 32; i++) {
 			ret = put_user(*reg, tmp);
@@ -397,8 +392,7 @@
 		unsigned long *reg = &((unsigned long *)child->thread.fpr)[0];
 		unsigned int __user *tmp = (unsigned int __user *)addr;
 
-		if (child->thread.regs->msr & MSR_FP)
-			giveup_fpu(child);
+		flush_fp_to_thread(child);
 
 		for (i = 0; i < 32; i++) {
 			ret = get_user(*reg, tmp);
diff -urN linux-2.5/arch/ppc64/kernel/rtas.c test25/arch/ppc64/kernel/rtas.c
--- linux-2.5/arch/ppc64/kernel/rtas.c	2004-05-22 09:08:53.000000000 +1000
+++ test25/arch/ppc64/kernel/rtas.c	2004-06-08 16:24:40.010838888 +1000
@@ -68,10 +68,11 @@
 void
 call_rtas_display_status(char c)
 {
-	struct rtas_args *args = &(get_paca()->xRtas);
+	struct rtas_args *args;
 	unsigned long s;
 
 	spin_lock_irqsave(&rtas.lock, s);
+	args = &(get_paca()->xRtas);
 
 	args->token = 10;
 	args->nargs = 1;
@@ -145,7 +146,7 @@
 	va_list list;
 	int i, logit = 0;
 	unsigned long s;
-	struct rtas_args *rtas_args = &(get_paca()->xRtas);
+	struct rtas_args *rtas_args;
 	long ret;
 
 	PPCDBG(PPCDBG_RTAS, "Entering rtas_call\n");
@@ -158,6 +159,7 @@
 
 	/* Gotta do something different here, use global lock for now... */
 	spin_lock_irqsave(&rtas.lock, s);
+	rtas_args = &(get_paca()->xRtas);
 
 	rtas_args->token = token;
 	rtas_args->nargs = nargs;
diff -urN linux-2.5/arch/ppc64/kernel/signal.c test25/arch/ppc64/kernel/signal.c
--- linux-2.5/arch/ppc64/kernel/signal.c	2004-06-01 08:11:19.000000000 +1000
+++ test25/arch/ppc64/kernel/signal.c	2004-06-08 16:25:15.899840320 +1000
@@ -131,8 +131,7 @@
 #endif
 	long err = 0;
 
-	if (regs->msr & MSR_FP)
-		giveup_fpu(current);
+	flush_fp_to_thread(current);
 
 	/* Make sure signal doesn't get spurrious FP exceptions */
 	current->thread.fpscr = 0;
@@ -141,9 +140,8 @@
 	err |= __put_user(v_regs, &sc->v_regs);
 
 	/* save altivec registers */
-	if (current->thread.used_vr) {		
-		if (regs->msr & MSR_VEC)
-			giveup_altivec(current);
+	if (current->thread.used_vr) {
+		flush_altivec_to_thread(current);
 		/* Copy 33 vec registers (vr0..31 and vscr) to the stack */
 		err |= __copy_to_user(v_regs, current->thread.vr, 33 * sizeof(vector128));
 		/* set MSR_VEC in the MSR value in the frame to indicate that sc->v_reg)
diff -urN linux-2.5/arch/ppc64/kernel/signal32.c test25/arch/ppc64/kernel/signal32.c
--- linux-2.5/arch/ppc64/kernel/signal32.c	2004-06-01 08:11:19.000000000 +1000
+++ test25/arch/ppc64/kernel/signal32.c	2004-06-08 16:25:26.220868592 +1000
@@ -130,11 +130,10 @@
 {
 	elf_greg_t64 *gregs = (elf_greg_t64 *)regs;
 	int i, err = 0;
-	
-	/* Make sure floating point registers are stored in regs */ 
-	if (regs->msr & MSR_FP)
-		giveup_fpu(current);
-	
+
+	/* Make sure floating point registers are stored in regs */
+	flush_fp_to_thread(current);
+
 	/* save general and floating-point registers */
 	for (i = 0; i <= PT_RESULT; i ++)
 		err |= __put_user((unsigned int)gregs[i], &frame->mc_gregs[i]);
@@ -148,8 +147,7 @@
 #ifdef CONFIG_ALTIVEC
 	/* save altivec registers */
 	if (current->thread.used_vr) {
-		if (regs->msr & MSR_VEC)
-			giveup_altivec(current);
+		flush_altivec_to_thread(current);
 		if (__copy_to_user(&frame->mc_vregs, current->thread.vr,
 				   ELF_NVRREG32 * sizeof(vector128)))
 			return 1;
diff -urN linux-2.5/arch/ppc64/kernel/sys_ppc32.c test25/arch/ppc64/kernel/sys_ppc32.c
--- linux-2.5/arch/ppc64/kernel/sys_ppc32.c	2004-06-01 08:11:19.000000000 +1000
+++ test25/arch/ppc64/kernel/sys_ppc32.c	2004-06-08 15:19:01.000000000 +1000
@@ -617,12 +617,8 @@
 	error = PTR_ERR(filename);
 	if (IS_ERR(filename))
 		goto out;
-	if (regs->msr & MSR_FP)
-		giveup_fpu(current);
-#ifdef CONFIG_ALTIVEC
-	if (regs->msr & MSR_VEC)
-		giveup_altivec(current);
-#endif /* CONFIG_ALTIVEC */
+	flush_fp_to_thread(current);
+	flush_altivec_to_thread(current);
 
 	error = compat_do_execve(filename, compat_ptr(a1), compat_ptr(a2), regs);
 
diff -urN linux-2.5/arch/ppc64/kernel/traps.c test25/arch/ppc64/kernel/traps.c
--- linux-2.5/arch/ppc64/kernel/traps.c	2004-05-22 09:08:53.000000000 +1000
+++ test25/arch/ppc64/kernel/traps.c	2004-06-08 16:26:54.933962616 +1000
@@ -308,8 +308,7 @@
 	siginfo_t info;
 	unsigned long fpscr;
 
-	if (regs->msr & MSR_FP)
-		giveup_fpu(current);
+	flush_fp_to_thread(current);
 
 	fpscr = current->thread.fpscr;
 
@@ -521,8 +520,7 @@
 void
 AltivecAssistException(struct pt_regs *regs)
 {
-	if (regs->msr & MSR_VEC)
-		giveup_altivec(current);
+	flush_altivec_to_thread(current);
 	/* XXX quick hack for now: set the non-Java bit in the VSCR */
 	current->thread.vscr.u[3] |= 0x10000;
 }
diff -urN linux-2.5/arch/ppc64/mm/hash_utils.c test25/arch/ppc64/mm/hash_utils.c
--- linux-2.5/arch/ppc64/mm/hash_utils.c	2004-04-01 06:59:36.000000000 +1000
+++ test25/arch/ppc64/mm/hash_utils.c	2004-06-08 13:51:25.000000000 +1000
@@ -251,6 +251,7 @@
 	struct mm_struct *mm;
 	pte_t *ptep;
 	int ret;
+	int cpu;
 	int user_region = 0;
 	int local = 0;
 	cpumask_t tmp;
@@ -302,7 +303,8 @@
 	if (pgdir == NULL)
 		return 1;
 
-	tmp = cpumask_of_cpu(smp_processor_id());
+	cpu = get_cpu();
+	tmp = cpumask_of_cpu(cpu);
 	if (user_region && cpus_equal(mm->cpu_vm_mask, tmp))
 		local = 1;
 
@@ -311,11 +313,13 @@
 		ret = hash_huge_page(mm, access, ea, vsid, local);
 	else {
 		ptep = find_linux_pte(pgdir, ea);
-		if (ptep == NULL)
+		if (ptep == NULL) {
+			put_cpu();
 			return 1;
+		}
 		ret = __hash_page(ea, access, vsid, ptep, trap, local);
 	}
-
+	put_cpu();
 
 	return ret;
 }
diff -urN linux-2.5/arch/ppc64/mm/hugetlbpage.c test25/arch/ppc64/mm/hugetlbpage.c
--- linux-2.5/arch/ppc64/mm/hugetlbpage.c	2004-05-23 17:45:55.000000000 +1000
+++ test25/arch/ppc64/mm/hugetlbpage.c	2004-06-08 13:52:16.000000000 +1000
@@ -375,6 +375,7 @@
 	unsigned long addr;
 	hugepte_t *ptep;
 	struct page *page;
+	int cpu;
 	int local = 0;
 	cpumask_t tmp;
 
@@ -383,7 +384,8 @@
 	BUG_ON((end % HPAGE_SIZE) != 0);
 
 	/* XXX are there races with checking cpu_vm_mask? - Anton */
-	tmp = cpumask_of_cpu(smp_processor_id());
+	cpu = get_cpu();
+	tmp = cpumask_of_cpu(cpu);
 	if (cpus_equal(vma->vm_mm->cpu_vm_mask, tmp))
 		local = 1;
 
@@ -406,6 +408,7 @@
 
 		put_page(page);
 	}
+	put_cpu();
 
 	mm->rss -= (end - start) >> PAGE_SHIFT;
 }
diff -urN linux-2.5/arch/ppc64/mm/init.c test25/arch/ppc64/mm/init.c
--- linux-2.5/arch/ppc64/mm/init.c	2004-05-28 07:16:52.000000000 +1000
+++ test25/arch/ppc64/mm/init.c	2004-06-08 13:52:50.000000000 +1000
@@ -764,6 +764,7 @@
 	void *pgdir;
 	pte_t *ptep;
 	int local = 0;
+	int cpu;
 	cpumask_t tmp;
 
 	/* handle i-cache coherency */
@@ -794,12 +795,14 @@
 
 	vsid = get_vsid(vma->vm_mm->context.id, ea);
 
-	tmp = cpumask_of_cpu(smp_processor_id());
+	cpu = get_cpu();
+	tmp = cpumask_of_cpu(cpu);
 	if (cpus_equal(vma->vm_mm->cpu_vm_mask, tmp))
 		local = 1;
 
 	__hash_page(ea, pte_val(pte) & (_PAGE_USER|_PAGE_RW), vsid, ptep,
 		    0x300, local);
+	put_cpu();
 }
 
 void * reserve_phb_iospace(unsigned long size)
diff -urN linux-2.5/arch/ppc64/mm/tlb.c test25/arch/ppc64/mm/tlb.c
--- linux-2.5/arch/ppc64/mm/tlb.c	2004-05-23 17:45:55.000000000 +1000
+++ test25/arch/ppc64/mm/tlb.c	2004-06-08 13:54:44.000000000 +1000
@@ -91,12 +91,15 @@
 void __flush_tlb_pending(struct ppc64_tlb_batch *batch)
 {
 	int i;
-	cpumask_t tmp = cpumask_of_cpu(smp_processor_id());
+	int cpu;
+	cpumask_t tmp;
 	int local = 0;
 
 	BUG_ON(in_interrupt());
 
+	cpu = get_cpu();
 	i = batch->index;
+	tmp = cpumask_of_cpu(cpu);
 	if (cpus_equal(batch->mm->cpu_vm_mask, tmp))
 		local = 1;
 
@@ -106,6 +109,7 @@
 	else
 		flush_hash_range(batch->context, i, local);
 	batch->index = 0;
+	put_cpu();
 }
 
 #ifdef CONFIG_SMP
diff -urN linux-2.5/include/asm-ppc64/hardirq.h test25/include/asm-ppc64/hardirq.h
--- linux-2.5/include/asm-ppc64/hardirq.h	2003-10-17 06:01:35.000000000 +1000
+++ test25/include/asm-ppc64/hardirq.h	2004-06-06 20:37:24.000000000 +1000
@@ -82,9 +82,11 @@
 
 #ifdef CONFIG_PREEMPT
 # define in_atomic()	((preempt_count() & ~PREEMPT_ACTIVE) != kernel_locked())
+# define preemptible()	(preempt_count() == 0 && !irqs_disabled())
 # define IRQ_EXIT_OFFSET (HARDIRQ_OFFSET-1)
 #else
 # define in_atomic()	(preempt_count() != 0)
+# define preemptible()	0
 # define IRQ_EXIT_OFFSET HARDIRQ_OFFSET
 #endif
 #define irq_exit()							\
diff -urN linux-2.5/include/asm-ppc64/system.h test25/include/asm-ppc64/system.h
--- linux-2.5/include/asm-ppc64/system.h	2004-05-22 09:08:54.000000000 +1000
+++ test25/include/asm-ppc64/system.h	2004-06-08 16:29:24.431868072 +1000
@@ -111,6 +111,8 @@
 extern int _get_PVR(void);
 extern void giveup_fpu(struct task_struct *);
 extern void disable_kernel_fp(void);
+extern void flush_fp_to_thread(struct task_struct *);
+extern void flush_altivec_to_thread(struct task_struct *);
 extern void enable_kernel_fp(void);
 extern void giveup_altivec(struct task_struct *);
 extern void disable_kernel_altivec(void);
diff -urN linux-2.5/include/asm-ppc64/thread_info.h test25/include/asm-ppc64/thread_info.h
--- linux-2.5/include/asm-ppc64/thread_info.h	2004-05-26 18:14:47.000000000 +1000
+++ test25/include/asm-ppc64/thread_info.h	2004-06-06 18:23:21.000000000 +1000
@@ -13,6 +13,7 @@
 #ifndef __ASSEMBLY__
 #include <linux/config.h>
 #include <asm/processor.h>
+#include <asm/page.h>
 #include <linux/stringify.h>
 
 /*
@@ -23,7 +24,7 @@
 	struct exec_domain *exec_domain;	/* execution domain */
 	unsigned long	flags;			/* low level flags */
 	int		cpu;			/* cpu we're on */
-	int		preempt_count;		/* not used at present */
+	int		preempt_count;
 	struct restart_block restart_block;
 };
 
@@ -73,7 +74,7 @@
 static inline struct thread_info *current_thread_info(void)
 {
 	struct thread_info *ti;
-	__asm__("clrrdi %0,1,14" : "=r"(ti));
+	__asm__("clrrdi %0,1,%1" : "=r"(ti) : "i" (THREAD_SHIFT));
 	return ti;
 }
 
@@ -83,6 +84,8 @@
 
 /*
  * thread information flag bit numbers
+ * N.B. If TIF_SIGPENDING or TIF_NEED_RESCHED are changed
+ * to be >= 4, code in entry.S will need to be changed.
  */
 #define TIF_SYSCALL_TRACE	0	/* syscall trace active */
 #define TIF_NOTIFY_RESUME	1	/* resumption notification requested */