From 9cc2c0f41c403a05989bc3ca2af650247d452f65 Mon Sep 17 00:00:00 2001

From: "T.kabe" <kabe@>

Date: Mon, 6 Mar 2017 15:18:55 +0900

Subject: [PATCH 2/4] vfs: Keep a list of mounts on a mount point

[upstream commit 0a5eb7c8189922e86a840972cd0b57e41de6f031]

Author: Eric W. Biederman <ebiederman@twitter.com>

Date:   Sun Sep 22 19:37:01 2013 -0700

    vfs: Keep a list of mounts on a mount point

    To spot any possible problems call BUG if a mountpoint

    is put when it's list of mounts is not empty.

    AV: use hlist instead of list_head

    Reviewed-by: Miklos Szeredi <miklos@szeredi.hu>

    Signed-off-by: Eric W. Biederman <ebiederman@twitter.com>

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

---

 fs/mount.h     | 2 ++

 fs/namespace.c | 6 ++++++

 2 files changed, 8 insertions(+)

diff --git a/fs/mount.h b/fs/mount.h

index b870800..92fecbe 100644

--- a/fs/mount.h

+++ b/fs/mount.h

@@ -21,6 +21,7 @@ struct mnt_pcp {

 struct mountpoint {

 	struct list_head m_hash;

 	struct dentry *m_dentry;

+	struct hlist_head m_list;

 	int m_count;

 };

@@ -47,6 +48,7 @@ struct mount {

 	struct mount *mnt_master;	/* slave is on master->mnt_slave_list */

 	struct mnt_namespace *mnt_ns;	/* containing namespace */

 	struct mountpoint *mnt_mp;	/* where is it mounted */

+	struct hlist_node mnt_mp_list;	/* list mounts with the same mountpoint */

 #ifdef CONFIG_FSNOTIFY

 	struct hlist_head mnt_fsnotify_marks;

 	__u32 mnt_fsnotify_mask;

diff --git a/fs/namespace.c b/fs/namespace.c

index 0053bfc..c238481 100644

--- a/fs/namespace.c

+++ b/fs/namespace.c

@@ -197,6 +197,7 @@ static struct mount *alloc_vfsmnt(const char *name)

 		INIT_LIST_HEAD(&mnt->mnt_share);

 		INIT_LIST_HEAD(&mnt->mnt_slave_list);

 		INIT_LIST_HEAD(&mnt->mnt_slave);

+		INIT_HLIST_NODE(&mnt->mnt_mp_list);

 #ifdef CONFIG_FSNOTIFY

 		INIT_HLIST_HEAD(&mnt->mnt_fsnotify_marks);

 #endif

@@ -636,6 +637,7 @@ static struct mountpoint *new_mountpoint(struct dentry *dentry)

 	mp->m_dentry = dentry;

 	mp->m_count = 1;

 	list_add(&mp->m_hash, chain);

+	INIT_HLIST_HEAD(&mp->m_list);

 	return mp;

 }

@@ -643,6 +645,7 @@ static void put_mountpoint(struct mountpoint *mp)

 {

 	if (!--mp->m_count) {

 		struct dentry *dentry = mp->m_dentry;

+		BUG_ON(!hlist_empty(&mp->m_list));

 		spin_lock(&dentry->d_lock);

 		dentry->d_flags &= ~DCACHE_MOUNTED;

 		spin_unlock(&dentry->d_lock);

@@ -689,6 +692,7 @@ static void detach_mnt(struct mount *mnt, struct path *old_path)

 	mnt->mnt_mountpoint = mnt->mnt.mnt_root;

 	list_del_init(&mnt->mnt_child);

 	list_del_init(&mnt->mnt_hash);

+	hlist_del_init(&mnt->mnt_mp_list);

 	put_mountpoint(mnt->mnt_mp);

 	mnt->mnt_mp = NULL;

 }

@@ -705,6 +709,7 @@ void mnt_set_mountpoint(struct mount *mnt,

 	child_mnt->mnt_mountpoint = dget(mp->m_dentry);

 	child_mnt->mnt_parent = mnt;

 	child_mnt->mnt_mp = mp;

+	hlist_add_head(&child_mnt->mnt_mp_list, &mp->m_list);

 }

 /*

@@ -1207,6 +1212,7 @@ void umount_tree(struct mount *mnt, int propagate)

 		__touch_mnt_namespace(p->mnt_ns);

 		p->mnt_ns = NULL;

 		if (mnt_has_parent(p)) {

+			hlist_del_init(&p->mnt_mp_list);

 			p->mnt_parent->mnt_ghosts++;

 			put_mountpoint(p->mnt_mp);

 			p->mnt_mp = NULL;

-- 

1.8.3.1