PREEMPT for ppc64

From: Paul Mackerras
Date: Mon Jun 07 2004 - 02:53:04 EST

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 */
-
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