mnt_init(): call shmem_init() unconditionally

No point having two call sites (earlier in init_rootfs() from
mnt_init() in case we are going to use shmem-style rootfs,
later from do_basic_setup() unconditionally), along with the
logics in shmem_init() itself to make the second call a no-op...
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/namespace.c

@@ -29,6 +29,7 @@
 #include <linux/sched/task.h>
 #include <uapi/linux/mount.h>
 #include <linux/fs_context.h>
+#include <linux/shmem_fs.h>
 
 #include "pnode.h"
 #include "internal.h"
@@ -3740,6 +3741,7 @@ void __init mnt_init(void)
 	fs_kobj = kobject_create_and_add("fs", NULL);
 	if (!fs_kobj)
 		printk(KERN_WARNING "%s: kobj create error\n", __func__);
+	shmem_init();
 	init_rootfs();
 	init_mount_tree();
 }

include/linux/init.h

@@ -148,7 +148,7 @@ extern unsigned int reset_devices;
 /* used by init/main.c */
 void setup_arch(char **);
 void prepare_namespace(void);
-int __init init_rootfs(void);
+void __init init_rootfs(void);
 extern struct file_system_type rootfs_fs_type;
 
 #if defined(CONFIG_STRICT_KERNEL_RWX) || defined(CONFIG_STRICT_MODULE_RWX)

init/do_mounts.c

@@ -643,14 +643,9 @@ struct file_system_type rootfs_fs_type = {
 	.kill_sb	= kill_litter_super,
 };
 
-int __init init_rootfs(void)
+void __init init_rootfs(void)
 {
-	int err = 0;
-
 	if (IS_ENABLED(CONFIG_TMPFS) && !saved_root_name[0] &&
-		(!root_fs_names || strstr(root_fs_names, "tmpfs"))) {
-		err = shmem_init();
+		(!root_fs_names || strstr(root_fs_names, "tmpfs")))
 		is_tmpfs = true;
-	}
-	return err;
 }

init/main.c

@@ -1000,7 +1000,6 @@ static void __init do_initcalls(void)
 static void __init do_basic_setup(void)
 {
 	cpuset_init_smp();
-	shmem_init();
 	driver_init();
 	init_irq_proc();
 	do_ctors();

mm/shmem.c

@@ -3775,10 +3775,6 @@ int __init shmem_init(void)
 {
 	int error;
 
-	/* If rootfs called this, don't re-init */
-	if (shmem_inode_cachep)
-		return 0;
-
 	shmem_init_inodecache();
 
 	error = register_filesystem(&shmem_fs_type);