pid namespaces: move alloc_pid() to copy_process()

Move alloc_pid() into copy_process().  This will keep all pid and pid
namespace code together and simplify error handling when we support multiple
pid namespaces.
Signed-off-by: NSukadev Bhattiprolu <sukadev@us.ibm.com>
Cc: Pavel Emelianov <xemul@openvz.org>
Cc: Eric W. Biederman <ebiederm@xmission.com>
Cc: Cedric Le Goater <clg@fr.ibm.com>
Cc: Dave Hansen <haveblue@us.ibm.com>
Cc: Serge Hallyn <serue@us.ibm.com>
Cc: Herbert Poetzel <herbert@13thfloor.at>
Cc: Kirill Korotaev <dev@sw.ru>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

kernel/fork.c

@@ -1040,6 +1040,12 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 	if (p->binfmt && !try_module_get(p->binfmt->module))
 		goto bad_fork_cleanup_put_domain;
 
+	if (pid != &init_struct_pid) {
+		pid = alloc_pid();
+		if (!pid)
+			goto bad_fork_put_binfmt_module;
+	}
+
 	p->did_exec = 0;
 	delayacct_tsk_init(p);	/* Must remain after dup_task_struct() */
 	copy_flags(clone_flags, p);
@@ -1331,6 +1337,9 @@ static struct task_struct *copy_process(unsigned long clone_flags,
 	cgroup_exit(p, cgroup_callbacks_done);
 bad_fork_cleanup_delays_binfmt:
 	delayacct_tsk_free(p);
+	if (pid != &init_struct_pid)
+		free_pid(pid);
+bad_fork_put_binfmt_module:
 	if (p->binfmt)
 		module_put(p->binfmt->module);
 bad_fork_cleanup_put_domain:
@@ -1395,19 +1404,16 @@ long do_fork(unsigned long clone_flags,
 {
 	struct task_struct *p;
 	int trace = 0;
-	struct pid *pid = alloc_pid();
 	long nr;
 
-	if (!pid)
-		return -EAGAIN;
-	nr = pid->nr;
 	if (unlikely(current->ptrace)) {
 		trace = fork_traceflag (clone_flags);
 		if (trace)
 			clone_flags |= CLONE_PTRACE;
 	}
 
-	p = copy_process(clone_flags, stack_start, regs, stack_size, parent_tidptr, child_tidptr, pid);
+	p = copy_process(clone_flags, stack_start, regs, stack_size,
+			parent_tidptr, child_tidptr, NULL);
 	/*
 	 * Do this prior waking up the new thread - the thread pointer
 	 * might get invalid after that point, if the thread exits quickly.
@@ -1415,6 +1421,8 @@ long do_fork(unsigned long clone_flags,
 	if (!IS_ERR(p)) {
 		struct completion vfork;
 
+		nr = pid_nr(task_pid(p));
+
 		if (clone_flags & CLONE_VFORK) {
 			p->vfork_done = &vfork;
 			init_completion(&vfork);
@@ -1448,7 +1456,6 @@ long do_fork(unsigned long clone_flags,
 			}
 		}
 	} else {
-		free_pid(pid);
 		nr = PTR_ERR(p);
 	}
 	return nr;