make struct mountpoint bear the dentry reference to mountpoint, not struct mount
Using dput_to_list() to shift the contributing reference from ->mnt_mountpoint
to ->mnt_mp->m_dentry. Dentries are dropped (with dput_to_list()) as soon
as struct mountpoint is destroyed; in cases where we are under namespace_sem
we use the global list, shrinking it in namespace_unlock(). In case of
detaching stuck MNT_LOCKed children at final mntput_no_expire() we use a local
list and shrink it ourselves. ->mnt_ex_mountpoint crap is gone.
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/namespace.c b/fs/namespace.c
index b7059a4..e0902fd 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -69,6 +69,8 @@ static struct hlist_head *mount_hashtable __read_mostly;
static struct hlist_head *mountpoint_hashtable __read_mostly;
static struct kmem_cache *mnt_cache __read_mostly;
static DECLARE_RWSEM(namespace_sem);
+static HLIST_HEAD(unmounted); /* protected by namespace_sem */
+static LIST_HEAD(ex_mountpoints); /* protected by namespace_sem */
/* /sys/fs */
struct kobject *fs_kobj;
@@ -172,7 +174,6 @@ unsigned int mnt_get_count(struct mount *mnt)
static void drop_mountpoint(struct fs_pin *p)
{
struct mount *m = container_of(p, struct mount, mnt_umount);
- dput(m->mnt_ex_mountpoint);
pin_remove(p);
mntput(&m->mnt);
}
@@ -739,7 +740,7 @@ static struct mountpoint *get_mountpoint(struct dentry *dentry)
/* Add the new mountpoint to the hash table */
read_seqlock_excl(&mount_lock);
- new->m_dentry = dentry;
+ new->m_dentry = dget(dentry);
new->m_count = 1;
hlist_add_head(&new->m_hash, mp_hash(dentry));
INIT_HLIST_HEAD(&new->m_list);
@@ -752,7 +753,11 @@ static struct mountpoint *get_mountpoint(struct dentry *dentry)
return mp;
}
-static void put_mountpoint(struct mountpoint *mp)
+/*
+ * vfsmount lock must be held. Additionally, the caller is responsible
+ * for serializing calls for given disposal list.
+ */
+static void __put_mountpoint(struct mountpoint *mp, struct list_head *list)
{
if (!--mp->m_count) {
struct dentry *dentry = mp->m_dentry;
@@ -760,11 +765,18 @@ static void put_mountpoint(struct mountpoint *mp)
spin_lock(&dentry->d_lock);
dentry->d_flags &= ~DCACHE_MOUNTED;
spin_unlock(&dentry->d_lock);
+ dput_to_list(dentry, list);
hlist_del(&mp->m_hash);
kfree(mp);
}
}
+/* called with namespace_lock and vfsmount lock */
+static void put_mountpoint(struct mountpoint *mp)
+{
+ __put_mountpoint(mp, &ex_mountpoints);
+}
+
static inline int check_mnt(struct mount *mnt)
{
return mnt->mnt_ns == current->nsproxy->mnt_ns;
@@ -813,7 +825,7 @@ static struct mountpoint *unhash_mnt(struct mount *mnt)
*/
static void detach_mnt(struct mount *mnt, struct path *old_path)
{
- old_path->dentry = mnt->mnt_mountpoint;
+ old_path->dentry = dget(mnt->mnt_mountpoint);
old_path->mnt = &mnt->mnt_parent->mnt;
put_mountpoint(unhash_mnt(mnt));
}
@@ -823,8 +835,6 @@ static void detach_mnt(struct mount *mnt, struct path *old_path)
*/
static void umount_mnt(struct mount *mnt)
{
- /* old mountpoint will be dropped when we can do that */
- mnt->mnt_ex_mountpoint = mnt->mnt_mountpoint;
put_mountpoint(unhash_mnt(mnt));
}
@@ -837,7 +847,7 @@ void mnt_set_mountpoint(struct mount *mnt,
{
mp->m_count++;
mnt_add_count(mnt, 1); /* essentially, that's mntget */
- child_mnt->mnt_mountpoint = dget(mp->m_dentry);
+ child_mnt->mnt_mountpoint = mp->m_dentry;
child_mnt->mnt_parent = mnt;
child_mnt->mnt_mp = mp;
hlist_add_head(&child_mnt->mnt_mp_list, &mp->m_list);
@@ -864,7 +874,6 @@ static void attach_mnt(struct mount *mnt,
void mnt_change_mountpoint(struct mount *parent, struct mountpoint *mp, struct mount *mnt)
{
struct mountpoint *old_mp = mnt->mnt_mp;
- struct dentry *old_mountpoint = mnt->mnt_mountpoint;
struct mount *old_parent = mnt->mnt_parent;
list_del_init(&mnt->mnt_child);
@@ -874,22 +883,6 @@ void mnt_change_mountpoint(struct mount *parent, struct mountpoint *mp, struct m
attach_mnt(mnt, parent, mp);
put_mountpoint(old_mp);
-
- /*
- * Safely avoid even the suggestion this code might sleep or
- * lock the mount hash by taking advantage of the knowledge that
- * mnt_change_mountpoint will not release the final reference
- * to a mountpoint.
- *
- * During mounting, the mount passed in as the parent mount will
- * continue to use the old mountpoint and during unmounting, the
- * old mountpoint will continue to exist until namespace_unlock,
- * which happens well after mnt_change_mountpoint.
- */
- spin_lock(&old_mountpoint->d_lock);
- old_mountpoint->d_lockref.count--;
- spin_unlock(&old_mountpoint->d_lock);
-
mnt_add_count(old_parent, -1);
}
@@ -1142,6 +1135,8 @@ static DECLARE_DELAYED_WORK(delayed_mntput_work, delayed_mntput);
static void mntput_no_expire(struct mount *mnt)
{
+ LIST_HEAD(list);
+
rcu_read_lock();
if (likely(READ_ONCE(mnt->mnt_ns))) {
/*
@@ -1182,10 +1177,11 @@ static void mntput_no_expire(struct mount *mnt)
if (unlikely(!list_empty(&mnt->mnt_mounts))) {
struct mount *p, *tmp;
list_for_each_entry_safe(p, tmp, &mnt->mnt_mounts, mnt_child) {
- umount_mnt(p);
+ __put_mountpoint(unhash_mnt(p), &list);
}
}
unlock_mount_hash();
+ shrink_dentry_list(&list);
if (likely(!(mnt->mnt.mnt_flags & MNT_INTERNAL))) {
struct task_struct *task = current;
@@ -1371,16 +1367,18 @@ int may_umount(struct vfsmount *mnt)
EXPORT_SYMBOL(may_umount);
-static HLIST_HEAD(unmounted); /* protected by namespace_sem */
-
static void namespace_unlock(void)
{
struct hlist_head head;
+ LIST_HEAD(list);
hlist_move_list(&unmounted, &head);
+ list_splice_init(&ex_mountpoints, &list);
up_write(&namespace_sem);
+ shrink_dentry_list(&list);
+
if (likely(hlist_empty(&head)))
return;