nilfs2: integrate sysfs support into driver

This patch integrates creation of sysfs groups and
attributes into NILFS file system driver.

It was found the issue with nilfs_sysfs_{create/delete}_snapshot_group
functions by Michael L Semon <mlsemon35@gmail.com> in the first
version of the patch:

  BUG: sleeping function called from invalid context at kernel/locking/mutex.c:579
  in_atomic(): 1, irqs_disabled(): 0, pid: 32676, name: umount.nilfs2
  2 locks held by umount.nilfs2/32676:
   #0:  (&type->s_umount_key#21){++++..}, at: [<790c18e2>] deactivate_super+0x37/0x58
   #1:  (&(&nilfs->ns_cptree_lock)->rlock){+.+...}, at: [<791bf659>] nilfs_put_root+0x23/0x5a
  Preemption disabled at:[<791bf659>] nilfs_put_root+0x23/0x5a

  CPU: 0 PID: 32676 Comm: umount.nilfs2 Not tainted 3.14.0+ #2
  Hardware name: Dell Computer Corporation Dimension 2350/07W080, BIOS A01 12/17/2002
  Call Trace:
    dump_stack+0x4b/0x75
    __might_sleep+0x111/0x16f
    mutex_lock_nested+0x1e/0x3ad
    kernfs_remove+0x12/0x26
    sysfs_remove_dir+0x3d/0x62
    kobject_del+0x13/0x38
    nilfs_sysfs_delete_snapshot_group+0xb/0xd
    nilfs_put_root+0x2a/0x5a
    nilfs_detach_log_writer+0x1ab/0x2c1
    nilfs_put_super+0x13/0x68
    generic_shutdown_super+0x60/0xd1
    kill_block_super+0x1d/0x60
    deactivate_locked_super+0x22/0x3f
    deactivate_super+0x3e/0x58
    mntput_no_expire+0xe2/0x141
    SyS_oldumount+0x70/0xa5
    syscall_call+0x7/0xb

The reason of the issue was placement of
nilfs_sysfs_{create/delete}_snapshot_group() call under
nilfs->ns_cptree_lock protection.  But this protection is unnecessary and
wrong solution.  The second version of the patch fixes this issue.

[fengguang.wu@intel.com: nilfs_sysfs_create_mounted_snapshots_group can be static]
Reported-by: Michael L. Semon <mlsemon35@gmail.com>
Signed-off-by: Vyacheslav Dubeyko <Vyacheslav.Dubeyko@hgst.com>
Cc: Vyacheslav Dubeyko <slava@dubeyko.com>
Cc: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
Tested-by: Michael L. Semon <mlsemon35@gmail.com>
Signed-off-by: Fengguang Wu <fengguang.wu@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/nilfs2/Makefile

@@ -2,4 +2,4 @@ obj-$(CONFIG_NILFS2_FS) += nilfs2.o
 nilfs2-y := inode.o file.o dir.o super.o namei.o page.o mdt.o \
 	btnode.o bmap.o btree.o direct.o dat.o recovery.o \
 	the_nilfs.o segbuf.o segment.o cpfile.o sufile.o \
-	ifile.o alloc.o gcinode.o ioctl.o
+	ifile.o alloc.o gcinode.o ioctl.o sysfs.o

fs/nilfs2/nilfs.h

@@ -320,6 +320,14 @@ int nilfs_gccache_wait_and_mark_dirty(struct buffer_head *);
 int nilfs_init_gcinode(struct inode *inode);
 void nilfs_remove_all_gcinodes(struct the_nilfs *nilfs);
 
+/* sysfs.c */
+int __init nilfs_sysfs_init(void);
+void nilfs_sysfs_exit(void);
+int nilfs_sysfs_create_device_group(struct super_block *);
+void nilfs_sysfs_delete_device_group(struct the_nilfs *);
+int nilfs_sysfs_create_snapshot_group(struct nilfs_root *);
+void nilfs_sysfs_delete_snapshot_group(struct nilfs_root *);
+
 /*
  * Inodes and files operations
  */

fs/nilfs2/super.c

@@ -1452,13 +1452,19 @@ static int __init init_nilfs_fs(void)
 	if (err)
 		goto fail;
 
-	err = register_filesystem(&nilfs_fs_type);
+	err = nilfs_sysfs_init();
 	if (err)
 		goto free_cachep;
 
+	err = register_filesystem(&nilfs_fs_type);
+	if (err)
+		goto deinit_sysfs_entry;
+
 	printk(KERN_INFO "NILFS version 2 loaded\n");
 	return 0;
 
+deinit_sysfs_entry:
+	nilfs_sysfs_exit();
 free_cachep:
 	nilfs_destroy_cachep();
 fail:
@@ -1468,6 +1474,7 @@ static int __init init_nilfs_fs(void)
 static void __exit exit_nilfs_fs(void)
 {
 	nilfs_destroy_cachep();
+	nilfs_sysfs_exit();
 	unregister_filesystem(&nilfs_fs_type);
 }
 

fs/nilfs2/sysfs.c

@@ -87,7 +87,7 @@ static struct kobj_type nilfs_##name##_ktype = { \
 };
 
 #define NILFS_DEV_INT_GROUP_FNS(name, parent_name) \
-int nilfs_sysfs_create_##name##_group(struct the_nilfs *nilfs) \
+static int nilfs_sysfs_create_##name##_group(struct the_nilfs *nilfs) \
 { \
 	struct kobject *parent; \
 	struct kobject *kobj; \
@@ -106,7 +106,7 @@ int nilfs_sysfs_create_##name##_group(struct the_nilfs *nilfs) \
 		return err; \
 	return 0; \
 } \
-void nilfs_sysfs_delete_##name##_group(struct the_nilfs *nilfs) \
+static void nilfs_sysfs_delete_##name##_group(struct the_nilfs *nilfs) \
 { \
 	kobject_del(&nilfs->ns_##parent_name##_subgroups->sg_##name##_kobj); \
 }

fs/nilfs2/the_nilfs.c

@@ -98,6 +98,7 @@ void destroy_nilfs(struct the_nilfs *nilfs)
 {
 	might_sleep();
 	if (nilfs_init(nilfs)) {
+		nilfs_sysfs_delete_device_group(nilfs);
 		brelse(nilfs->ns_sbh[0]);
 		brelse(nilfs->ns_sbh[1]);
 	}
@@ -641,6 +642,10 @@ int init_nilfs(struct the_nilfs *nilfs, struct super_block *sb, char *data)
 	if (err)
 		goto failed_sbh;
 
+	err = nilfs_sysfs_create_device_group(sb);
+	if (err)
+		goto failed_sbh;
+
 	set_nilfs_init(nilfs);
 	err = 0;
  out:
@@ -741,12 +746,13 @@ nilfs_find_or_create_root(struct the_nilfs *nilfs, __u64 cno)
 {
 	struct rb_node **p, *parent;
 	struct nilfs_root *root, *new;
+	int err;
 
 	root = nilfs_lookup_root(nilfs, cno);
 	if (root)
 		return root;
 
-	new = kmalloc(sizeof(*root), GFP_KERNEL);
+	new = kzalloc(sizeof(*root), GFP_KERNEL);
 	if (!new)
 		return NULL;
 
@@ -783,6 +789,12 @@ nilfs_find_or_create_root(struct the_nilfs *nilfs, __u64 cno)
 
 	spin_unlock(&nilfs->ns_cptree_lock);
 
+	err = nilfs_sysfs_create_snapshot_group(new);
+	if (err) {
+		kfree(new);
+		new = NULL;
+	}
+
 	return new;
 }
 
@@ -791,6 +803,8 @@ void nilfs_put_root(struct nilfs_root *root)
 	if (atomic_dec_and_test(&root->count)) {
 		struct the_nilfs *nilfs = root->nilfs;
 
+		nilfs_sysfs_delete_snapshot_group(root);
+
 		spin_lock(&nilfs->ns_cptree_lock);
 		rb_erase(&root->rb_node, &nilfs->ns_cptree);
 		spin_unlock(&nilfs->ns_cptree_lock);