Mark CLONE_DETACHED as being irrelevant: it must match CLONE_THREAD.

CLONE_THREAD without CLONE_DETACHED will now return -EINVAL, and
for a while we will warn about anything that uses it (there are no
known users, but this will help pinpoint any problems if somebody
used to care about the invalid combination).

include/linux/sched.h

@@ -49,7 +49,7 @@ struct exec_domain;
 #define CLONE_SETTLS	0x00080000	/* create a new TLS for the child */
 #define CLONE_PARENT_SETTID	0x00100000	/* set the TID in the parent */
 #define CLONE_CHILD_CLEARTID	0x00200000	/* clear the TID in the child */
-#define CLONE_DETACHED		0x00400000	/* parent wants no child-exit signal */
+#define CLONE_DETACHED		0x00400000	/* Not used - CLONE_THREAD implies detached uniquely */
 #define CLONE_UNTRACED		0x00800000	/* set if the tracing process can't force CLONE_PTRACE on this clone */
 #define CLONE_CHILD_SETTID	0x01000000	/* set the TID in the child */
 #define CLONE_STOPPED		0x02000000	/* Start in stopped state */

kernel/fork.c

@@ -746,8 +746,22 @@ struct task_struct *copy_process(unsigned long clone_flags,
 	 */
 	if ((clone_flags & CLONE_THREAD) && !(clone_flags & CLONE_SIGHAND))
 		return ERR_PTR(-EINVAL);
-	if ((clone_flags & CLONE_DETACHED) && !(clone_flags & CLONE_THREAD))
+
+	/*
+	 * CLONE_DETACHED must match CLONE_THREAD: it's a historical
+	 * thing.
+	 */
+	if (!(clone_flags & CLONE_DETACHED) != !(clone_flags & CLONE_THREAD)) {
+		/* Warn about the old no longer supported case so that we see it */
+		if (clone_flags & CLONE_THREAD) {
+			static int count;
+			if (count < 5) {
+				count++;
+				printk(KERN_WARNING "%s trying to use CLONE_THREAD without CLONE_DETACH\n", current->comm);
+			}
+		}
 		return ERR_PTR(-EINVAL);
+	}
 
 	retval = security_task_create(clone_flags);
 	if (retval)
@@ -877,10 +891,7 @@ struct task_struct *copy_process(unsigned long clone_flags,
 	p->parent_exec_id = p->self_exec_id;
 
 	/* ok, now we should be set up.. */
-	if (clone_flags & CLONE_DETACHED)
-		p->exit_signal = -1;
-	else
-		p->exit_signal = clone_flags & CSIGNAL;
+	p->exit_signal = (clone_flags & CLONE_THREAD) ? -1 : (clone_flags & CSIGNAL);
 	p->pdeath_signal = 0;
 
 	/*