[PATCH] 2.5: preempt on UP critical fix

During 2.5.5-pre schedule_tail was optimized away under UP.  We need it
for preempt-kernel, too, since it decrements the preempt_count to 0
coming off do_fork.

Without this patch, CONFIG_PREEMPT + !CONFIG_SMP does not gain one very
much.  

	Robert Love

arch/alpha/kernel/entry.S

@@ -495,7 +495,7 @@ alpha_switch_to:
 	ret	$31,($26),1
 .end alpha_switch_to
 
-#ifdef CONFIG_SMP
+#if CONFIG_SMP || CONFIG_PREEMPT
 .globl  ret_from_fork
 .align 3
 .ent ret_from_fork

arch/i386/kernel/entry.S

@@ -195,7 +195,7 @@ ENTRY(lcall27)
 
 
 ENTRY(ret_from_fork)
-#if CONFIG_SMP
+#if CONFIG_SMP || CONFIG_PREEMPT
 	call SYMBOL_NAME(schedule_tail)
 #endif
 	GET_THREAD_INFO(%ebx)

arch/ppc/kernel/entry.S

@@ -332,7 +332,7 @@ END_FTR_SECTION_IFSET(CPU_FTR_ALTIVEC)
 
 	.globl	ret_from_fork
 ret_from_fork:
-#ifdef CONFIG_SMP
+#if CONFIG_SMP || CONFIG_PREEMPT
 	bl	schedule_tail
 #endif
 	rlwinm	r3,r1,0,0,18

arch/ppc64/kernel/entry.S

@@ -311,7 +311,7 @@ _GLOBAL(_switch)
 	blr
 
 _GLOBAL(ret_from_fork)
-#ifdef CONFIG_SMP
+#if CONFIG_SMP || CONFIG_PREEMPT
 	bl	.schedule_tail
 #endif
 	clrrdi	r4,r1,THREAD_SHIFT

arch/s390/kernel/entry.S

@@ -295,7 +295,7 @@ ret_from_fork:
         stosm   24(%r15),0x03     # reenable interrupts
         sr      %r0,%r0           # child returns 0
         st      %r0,SP_R2(%r15)   # store return value (change R2 on stack)
-#ifdef CONFIG_SMP
+#if CONFIG_SMP || CONFIG_PREEMPT
         l       %r1,BASED(.Lschedtail)
 	la      %r14,BASED(sysc_return)
         br      %r1               # call schedule_tail, return to sysc_return
@@ -896,7 +896,7 @@ restart_go:
 #error .Ltrace:       .long  syscall_trace
 .Lvfork:       .long  sys_vfork
 
-#ifdef CONFIG_SMP
+#if CONFIG_SMP || CONFIG_PREEMPT
 .Lschedtail:   .long  schedule_tail
 #endif
 

arch/s390x/kernel/entry.S

@@ -280,7 +280,7 @@ ret_from_fork:
         GET_CURRENT               # load pointer to task_struct to R9
         stosm   48(%r15),0x03     # reenable interrupts
 	xc      SP_R2(8,%r15),SP_R2(%r15) # child returns 0
-#ifdef CONFIG_SMP
+#if CONFIG_SMP || CONFIG_PREEMPT
 	larl    %r14,sysc_return
         jg      schedule_tail     # return to sysc_return
 #else

kernel/sched.c

@@ -397,7 +397,7 @@ void sched_exit(task_t * p)
 			p->sleep_avg) / (EXIT_WEIGHT + 1);
 }
 
-#if CONFIG_SMP
+#if CONFIG_SMP || CONFIG_PREEMPT
 asmlinkage void schedule_tail(void)
 {
 	spin_unlock_irq(&this_rq()->lock);