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>

1 files changed, 8 insertions, 0 deletions

diff --git a/include/linux/syscalls.h b/include/linux/syscalls.h
index 19439c75c5b2..727f0cd73921 100644
--- a/include/linux/syscalls.h
+++ b/include/linux/syscalls.h
@@ -827,7 +827,15 @@ asmlinkage long sys_fanotify_mark(int fanotify_fd, unsigned int flags,
                                   const char  __user *pathname);
 asmlinkage long sys_syncfs(int fd);
 
+#ifndef CONFIG_GENERIC_KERNEL_EXECVE
 int kernel_execve(const char *filename, const char *const argv[], const char *const envp[]);
+#else
+#define kernel_execve(filename, argv, envp) \
+        do_execve(filename, \
+                (const char __user *const __user *)argv, \
+                (const char __user *const __user *)envp, \
+                current_pt_regs())
+#endif
 
 
 asmlinkage long sys_perf_event_open(