infrastructure for saner ret_from_kernel_thread semantics

* allow kernel_execve() leave the actual return to userland to
caller (selected by CONFIG_GENERIC_KERNEL_EXECVE).  Callers
updated accordingly.
* architecture that does select GENERIC_KERNEL_EXECVE in its
Kconfig should have its ret_from_kernel_thread() do this:
	call schedule_tail
	call the callback left for it by copy_thread(); if it ever
returns, that's because it has just done successful kernel_execve()
	jump to return from syscall
IOW, its only difference from ret_from_fork() is that it does call the
callback.
* such an architecture should also get rid of ret_from_kernel_execve()
and __ARCH_WANT_KERNEL_EXECVE

This is the last part of infrastructure patches in that area - from
that point on work on different architectures can live independently.

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

2 files changed, 4 insertions, 0 deletions

diff --git a/kernel/kmod.c b/kernel/kmod.c
index b6e5ca9c758a..1c317e386831 100644
--- a/kernel/kmod.c
+++ b/kernel/kmod.c
@@ -37,6 +37,7 @@
 #include <linux/notifier.h>
 #include <linux/suspend.h>
 #include <linux/rwsem.h>
+#include <linux/ptrace.h>
 #include <asm/uaccess.h>
 
 #include <trace/events/module.h>
@@ -221,6 +222,8 @@ static int ____call_usermodehelper(void *data)
         retval = kernel_execve(sub_info->path,
                                (const char *const *)sub_info->argv,
                                (const char *const *)sub_info->envp);
+        if (!retval)
+                return 0;
 
         /* Exec failed? */
 fail:
diff --git a/kernel/kthread.c b/kernel/kthread.c
index b579af57ea10..7ba65c1aa6b3 100644
--- a/kernel/kthread.c
+++ b/kernel/kthread.c
@@ -16,6 +16,7 @@
 #include <linux/mutex.h>
 #include <linux/slab.h>
 #include <linux/freezer.h>
+#include <linux/ptrace.h>
 #include <trace/events/sched.h>
 
 static DEFINE_SPINLOCK(kthread_create_lock);