preparation for generic kernel_thread()

Let architectures select GENERIC_KERNEL_THREAD and have their copy_thread()
treat NULL regs as "it came from kernel_thread(), sp argument contains
the function new thread will be calling and stack_size - the argument for
that function".  Switching the architectures begins shortly...

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

1 files changed, 12 insertions, 1 deletions

diff --git a/kernel/fork.c b/kernel/fork.c
index 2c8857e12855..a42c62a8eb24 100644
--- a/kernel/fork.c
+++ b/kernel/fork.c
@@ -1609,7 +1609,7 @@ long do_fork(unsigned long clone_flags,
          * requested, no event is reported; otherwise, report if the event
          * for the type of forking is enabled.
          */
-        if (likely(user_mode(regs)) && !(clone_flags & CLONE_UNTRACED)) {
+        if (!(clone_flags & CLONE_UNTRACED) && likely(user_mode(regs))) {
                 if (clone_flags & CLONE_VFORK)
                         trace = PTRACE_EVENT_VFORK;
                 else if ((clone_flags & CSIGNAL) != SIGCHLD)
@@ -1659,6 +1659,17 @@ long do_fork(unsigned long clone_flags,
         return nr;
 }
 
+#ifdef CONFIG_GENERIC_KERNEL_THREAD
+/*
+ * Create a kernel thread.
+ */
+pid_t kernel_thread(int (*fn)(void *), void *arg, unsigned long flags)
+{
+        return do_fork(flags|CLONE_VM|CLONE_UNTRACED, (unsigned long)fn, NULL,
+                (unsigned long)arg, NULL, NULL);
+}
+#endif
+
 #ifndef ARCH_MIN_MMSTRUCT_ALIGN
 #define ARCH_MIN_MMSTRUCT_ALIGN 0
 #endif