[PATCH][PPC32] Fix preemptible check

[Paul Mackerras]

Ben H added a check in a couple of places to make sure that we had
preemption disabled when we call enable_kernel_{fp,altivec}.
Unfortunately the check he used trips in the case when
CONFIG_PREEMPT=n.  This patch fixes it by defining a preemptible()
macro (which reduces to 0 when CONFIG_PREEMPT=n) and doing
WARN_ON(preemptible()).

Signed-off-by: Paul Mackerras <paulus@xxxxxxxxx>

diff -urN linux-2.5/arch/ppc/kernel/process.c pmac-2.5/arch/ppc/kernel/process.c
--- linux-2.5/arch/ppc/kernel/process.c	2004-05-11 07:53:04.000000000 +1000
+++ pmac-2.5/arch/ppc/kernel/process.c	2004-06-03 12:13:02.000000000 +1000
@@ -163,7 +163,7 @@
 void
 enable_kernel_altivec(void)
 {
-	WARN_ON(current_thread_info()->preempt_count == 0 && !irqs_disabled());
+	WARN_ON(preemptible());
 
 #ifdef CONFIG_SMP
 	if (current->thread.regs && (current->thread.regs->msr & MSR_VEC))
@@ -180,7 +180,7 @@
 void
 enable_kernel_fp(void)
 {
-	WARN_ON(current_thread_info()->preempt_count == 0 && !irqs_disabled());
+	WARN_ON(preemptible());
 
 #ifdef CONFIG_SMP
 	if (current->thread.regs && (current->thread.regs->msr & MSR_FP))
diff -urN linux-2.5/include/asm-ppc/hardirq.h pmac-2.5/include/asm-ppc/hardirq.h
--- linux-2.5/include/asm-ppc/hardirq.h	2003-09-24 10:56:02.000000000 +1000
+++ pmac-2.5/include/asm-ppc/hardirq.h	2004-06-03 21:36:45.938019448 +1000
@@ -83,11 +83,15 @@
 
 #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()							\
 do {									\
 	preempt_count() -= IRQ_EXIT_OFFSET;				\
-
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