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Subject[PATCH 04/12] 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.

Reviewed-by: Miklos Szeredi <miklos@szeredi.hu>
Signed-off-by: Eric W. Biederman <ebiederman@twitter.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 18511835dc28..5375da0dc570 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 abe2f56efaea..32d380eabdac 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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