diff -urNp ref/arch/um/include/user_util.h o1/arch/um/include/user_util.h
--- ref/arch/um/include/user_util.h	Sat Jul 20 13:58:53 2002
+++ o1/arch/um/include/user_util.h	Sat Jul 20 13:59:07 2002
@@ -111,6 +111,7 @@ extern int arch_handle_signal(int sig, s
 extern void user_time_init(void);
 extern unsigned long pid_pc(int pid);
 extern int arch_fixup(unsigned long address, void *sc_ptr);
+extern void forward_pending_sigio(int target);
 
 #endif
 
diff -urNp ref/arch/um/kernel/init_task.c o1/arch/um/kernel/init_task.c
--- ref/arch/um/kernel/init_task.c	Sat Jul 20 13:58:53 2002
+++ o1/arch/um/kernel/init_task.c	Sat Jul 20 13:59:07 2002
@@ -6,6 +6,7 @@
 #include "linux/mm.h"
 #include "linux/sched.h"
 #include "linux/version.h"
+#include "linux/sched_runqueue.h"
 #include "asm/uaccess.h"
 #include "asm/pgtable.h"
 #include "user_util.h"
diff -urNp ref/arch/um/kernel/process.c o1/arch/um/kernel/process.c
--- ref/arch/um/kernel/process.c	Sat Jul 20 13:58:53 2002
+++ o1/arch/um/kernel/process.c	Sat Jul 20 13:59:07 2002
@@ -233,6 +233,16 @@ int run_kernel_thread(int (*fn)(void *),
 	return(0);
 }
 
+void forward_pending_sigio(int target)
+{
+	sigset_t sigs;
+
+	if(sigpending(&sigs)) 
+		panic("forward_pending_sigio : sigpending failed");
+	if(sigismember(&sigs, SIGIO))
+		kill(target, SIGIO);
+}
+
 /*
  * Overrides for Emacs so that we follow Linus's tabbing style.
  * Emacs will notice this stuff at the end of the file and automatically
diff -urNp ref/arch/um/kernel/process_kern.c o1/arch/um/kernel/process_kern.c
--- ref/arch/um/kernel/process_kern.c	Sat Jul 20 13:58:53 2002
+++ o1/arch/um/kernel/process_kern.c	Sat Jul 20 13:59:11 2002
@@ -138,7 +138,7 @@ unsigned long alloc_stack(int order)
 	return(page);
 }
 
-extern void schedule_tail(struct task_struct *prev);
+asmlinkage void schedule_tail(task_t *prev);
 
 static void new_thread_handler(int sig)
 {
@@ -153,8 +153,10 @@ static void new_thread_handler(int sig)
 	free_page(current->thread.temp_stack);
 	set_cmdline("(kernel thread)");
 	force_flush_all();
+#ifdef CONFIG_SMP
 	if(current->thread.prev_sched != NULL)
 		schedule_tail(current->thread.prev_sched);
+#endif
 	current->thread.prev_sched = NULL;
 	change_sig(SIGUSR1, 1);
 	unblock_signals();
@@ -202,7 +204,6 @@ void *_switch_to(void *prev, void *next)
 	unsigned long flags;
 	int vtalrm, alrm, prof, err;
 	char c;
-	static int reading;
 
 	from = prev;
 	to = next;
@@ -210,46 +211,29 @@ void *_switch_to(void *prev, void *next)
 	to->thread.prev_sched = from;
 
 	if(CPU(from) == 0) forward_interrupts(to->thread.extern_pid);
+#ifdef CONFIG_SMP
 	forward_ipi(cpu_data[CPU(from)].ipi_pipe[0], to->thread.extern_pid);
+#endif
 	local_irq_save(flags);
 
 	vtalrm = change_sig(SIGVTALRM, 0);
 	alrm = change_sig(SIGALRM, 0);
 	prof = change_sig(SIGPROF, 0);
 
+	forward_pending_sigio(to->thread.extern_pid);
+
 	c = 0;
 	set_current(to);
-
-	reading = 0;
 	err = user_write(to->thread.switch_pipe[1], &c, sizeof(c));
 	if(err != sizeof(c))
 		panic("write of switch_pipe failed, errno = %d", -err);
 
-	reading = 1;
 	if(from->state == TASK_ZOMBIE) os_kill_process(os_getpid());
 
 	err = user_read(from->thread.switch_pipe[0], &c, sizeof(c));
 	if(err != sizeof(c))
 		panic("read of switch_pipe failed, errno = %d", -err);
 
-	/* This works around a nasty race with 'jail'.  If we are switching
-	 * between two threads of a threaded app and the incoming process 
-	 * runs before the outgoing process reaches the read, and it makes
-	 * it all the way out to userspace, then it will have write-protected 
-	 * the outgoing process stack.  Then, when the outgoing process 
-	 * returns from the write, it will segfault because it can no longer
-	 * write its own stack.  So, in order to avoid that, the incoming 
-	 * thread sits in a loop yielding until 'reading' is set.  This 
-	 * isn't entirely safe, since there may be a reschedule from a timer
-	 * happening between setting 'reading' and sleeping in read.  But,
-	 * it should get a whole quantum in which to reach the read and sleep,
-	 * which should be enough.
-	 */
-
-	if(jail){
-		while(!reading) sched_yield();
-	}
-
 	change_sig(SIGVTALRM, vtalrm);
 	change_sig(SIGALRM, alrm);
 	change_sig(SIGPROF, prof);
@@ -289,8 +273,10 @@ void finish_fork_handler(int sig)
 	if(current->mm != current->p_pptr->mm)
 		protect(uml_reserved, high_physmem - uml_reserved, 1, 1, 0, 1);
 	task_protections((unsigned long) current);
+#ifdef CONFIG_SMP
 	if(current->thread.prev_sched != NULL)
 		schedule_tail(current->thread.prev_sched);
+#endif
 	current->thread.prev_sched = NULL;
 
 	free_page(current->thread.temp_stack);