linux-kernel - [PATCH 04/11] vfs: Keep a list of mounts on a mount point

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Date:	Sat, 15 Feb 2014 13:37:03 -0800
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Al Viro <viro@...iv.linux.org.uk>
Cc:	"Serge E. Hallyn" <serge@...lyn.com>,
	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>,
	Rob Landley <rob@...dley.net>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Miklos Szeredi <miklos@...redi.hu>,
	Christoph Hellwig <hch@...radead.org>,
	Karel Zak <kzak@...hat.com>,
	"J. Bruce Fields" <bfields@...ldses.org>
Subject: [PATCH 04/11] 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.

Signed-off-by: Eric W. Biederman <ebiederman@...tter.com>
---
 fs/mount.h     |    2 ++
 fs/namespace.c |    6 ++++++
 2 files changed, 8 insertions(+), 0 deletions(-)

diff --git a/fs/mount.h b/fs/mount.h
index 17d913d86add..50a72d46e7a6 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 list_head m_list;
 	int m_count;
 };
 
@@ -48,6 +49,7 @@ 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 list_head 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 6dc23614d44d..33db9e95bd5c 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -195,6 +195,7 @@ 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_LIST_HEAD(&mnt->mnt_mp_list);
 #ifdef CONFIG_FSNOTIFY
 		INIT_HLIST_HEAD(&mnt->mnt_fsnotify_marks);
 #endif
@@ -695,6 +696,7 @@ static struct mountpoint *new_mountpoint(struct dentry *dentry)
 	mp->m_dentry = dentry;
 	mp->m_count = 1;
 	list_add(&mp->m_hash, chain);
+	INIT_LIST_HEAD(&mp->m_list);
 	return mp;
 }
 
@@ -702,6 +704,7 @@ static void put_mountpoint(struct mountpoint *mp)
 {
 	if (!--mp->m_count) {
 		struct dentry *dentry = mp->m_dentry;
+		BUG_ON(!list_empty(&mp->m_list));
 		spin_lock(&dentry->d_lock);
 		dentry->d_flags &= ~DCACHE_MOUNTED;
 		spin_unlock(&dentry->d_lock);
@@ -748,6 +751,7 @@ 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);
+	list_del_init(&mnt->mnt_mp_list);
 	put_mountpoint(mnt->mnt_mp);
 	mnt->mnt_mp = NULL;
 }
@@ -764,6 +768,7 @@ 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;
+	list_add_tail(&child_mnt->mnt_mp_list, &mp->m_list);
 }
 
 /*
@@ -1246,6 +1251,7 @@ void umount_tree(struct mount *mnt, int how)
 			p->mnt.mnt_flags |= MNT_SYNC_UMOUNT;
 		list_del_init(&p->mnt_child);
 		if (mnt_has_parent(p)) {
+			list_del_init(&p->mnt_mp_list);
 			put_mountpoint(p->mnt_mp);
 			/* move the reference to mountpoint into ->mnt_ex_mountpoint */
 			p->mnt_ex_mountpoint.dentry = p->mnt_mountpoint;
-- 
1.7.5.4

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