x86, um: convert to saner kernel_execve() semantics

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

arch/um/include/asm/processor-generic.h

@@ -26,7 +26,6 @@ struct thread_struct {
 	jmp_buf *fault_catcher;
 	struct task_struct *prev_sched;
 	unsigned long temp_stack;
-	jmp_buf *exec_buf;
 	struct arch_thread arch;
 	jmp_buf switch_buf;
 	int mm_count;
@@ -54,7 +53,6 @@ struct thread_struct {
 	.fault_addr		= NULL, \
 	.prev_sched		= NULL, \
 	.temp_stack		= 0, \
-	.exec_buf		= NULL, \
 	.arch			= INIT_ARCH_THREAD, \
 	.request		= { 0 } \
 }

arch/um/include/shared/os.h

@@ -191,7 +191,6 @@ extern int os_getpid(void);
 extern int os_getpgrp(void);
 
 extern void init_new_thread_signals(void);
-extern int run_kernel_thread(int (*fn)(void *), void *arg, jmp_buf **jmp_ptr);
 
 extern int os_map_memory(void *virt, int fd, unsigned long long off,
 			 unsigned long len, int r, int w, int x);

arch/um/kernel/exec.c

@@ -47,8 +47,3 @@ void start_thread(struct pt_regs *regs, unsigned long eip, unsigned long esp)
 #endif
 }
 EXPORT_SYMBOL(start_thread);
-
-void __noreturn ret_from_kernel_execve(struct pt_regs *unused)
-{
-	UML_LONGJMP(current->thread.exec_buf, 1);
-}

arch/um/kernel/process.c

@@ -135,14 +135,10 @@ void new_thread_handler(void)
 	arg = current->thread.request.u.thread.arg;
 
 	/*
-	 * The return value is 1 if the kernel thread execs a process,
-	 * 0 if it just exits
+	 * callback returns only if the kernel thread execs a process
 	 */
-	n = run_kernel_thread(fn, arg, &current->thread.exec_buf);
-	if (n == 1)
-		userspace(&current->thread.regs.regs);
-	else
-		do_exit(0);
+	n = fn(arg);
+	userspace(&current->thread.regs.regs);
 }
 
 /* Called magically, see new_thread_handler above */

arch/um/os-Linux/process.c

@@ -244,16 +244,3 @@ void init_new_thread_signals(void)
 	signal(SIGWINCH, SIG_IGN);
 	signal(SIGTERM, SIG_DFL);
 }
-
-int run_kernel_thread(int (*fn)(void *), void *arg, jmp_buf **jmp_ptr)
-{
-	jmp_buf buf;
-	int n;
-
-	*jmp_ptr = &buf;
-	n = UML_SETJMP(&buf);
-	if (n != 0)
-		return n;
-	(*fn)(arg);
-	return 0;
-}