[PATCH 6/6] switch the remnants of releasing the mountpoint away from fs_pin

Al Viro
2019-07-06T00:22:49Z

We used to need rather convoluted ordering trickery to guarantee
that dput() of ex-mountpoints happens before the final mntput()
of the same. Since we don't need that anymore, there's no point
playing with fs_pin for that.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
---
fs/fs_pin.c | 10 ++--------
fs/mount.h | 7 +++++--
fs/namespace.c | 37 +++++++++++++++++++------------------
include/linux/fs_pin.h | 1 -
4 files changed, 26 insertions(+), 29 deletions(-)

diff --git a/fs/fs_pin.c b/fs/fs_pin.c
index a6497cf8ae53..47ef3c71ce90 100644
--- a/fs/fs_pin.c
+++ b/fs/fs_pin.c
@@ -19,20 +19,14 @@ void pin_remove(struct fs_pin *pin)
spin_unlock_irq(&pin->wait.lock);
}

-void pin_insert_group(struct fs_pin *pin, struct vfsmount *m, struct hlist_head *p)
+void pin_insert(struct fs_pin *pin, struct vfsmount *m)
{
spin_lock(&pin_lock);
- if (p)
- hlist_add_head(&pin->s_list, p);
+ hlist_add_head(&pin->s_list, &m->mnt_sb->s_pins);
hlist_add_head(&pin->m_list, &real_mount(m)->mnt_pins);
spin_unlock(&pin_lock);
}

-void pin_insert(struct fs_pin *pin, struct vfsmount *m)
-{
- pin_insert_group(pin, m, &m->mnt_sb->s_pins);
-}
-
void pin_kill(struct fs_pin *p)
{
wait_queue_entry_t wait;
diff --git a/fs/mount.h b/fs/mount.h
index 84aa8cdf4971..711a4093e475 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -58,7 +58,10 @@ 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 */
+ union {
+ struct hlist_node mnt_mp_list; /* list mounts with the same mountpoint */
+ struct hlist_node mnt_umount;
+ };
struct list_head mnt_umounting; /* list entry for umount propagation */
#ifdef CONFIG_FSNOTIFY
struct fsnotify_mark_connector __rcu *mnt_fsnotify_marks;
@@ -68,7 +71,7 @@ struct mount {
int mnt_group_id; /* peer group identifier */
int mnt_expiry_mark; /* true if marked for expiry */
struct hlist_head mnt_pins;
- struct fs_pin mnt_umount;
+ struct hlist_head mnt_stuck_children;
} __randomize_layout;

#define MNT_NS_INTERNAL ERR_PTR(-EINVAL) /* distinct from any mnt_namespace */
diff --git a/fs/namespace.c b/fs/namespace.c
index 326a9ab591bc..a5d0eac9749d 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -171,13 +171,6 @@ unsigned int mnt_get_count(struct mount *mnt)
#endif
}

-static void drop_mountpoint(struct fs_pin *p)
-{
- struct mount *m = container_of(p, struct mount, mnt_umount);
- pin_remove(p);
- mntput(&m->mnt);
-}
-
static struct mount *alloc_vfsmnt(const char *name)
{
struct mount *mnt = kmem_cache_zalloc(mnt_cache, GFP_KERNEL);
@@ -215,7 +208,7 @@ static struct mount *alloc_vfsmnt(const char *name)
INIT_LIST_HEAD(&mnt->mnt_slave);
INIT_HLIST_NODE(&mnt->mnt_mp_list);
INIT_LIST_HEAD(&mnt->mnt_umounting);
- init_fs_pin(&mnt->mnt_umount, drop_mountpoint);
+ INIT_HLIST_HEAD(&mnt->mnt_stuck_children);
}
return mnt;

@@ -1079,19 +1072,22 @@ static struct mount *clone_mnt(struct mount *old, struct dentry *root,

static void cleanup_mnt(struct mount *mnt)
{
+ struct hlist_node *p;
+ struct mount *m;
/*
- * This probably indicates that somebody messed
- * up a mnt_want/drop_write() pair. If this
- * happens, the filesystem was probably unable
- * to make r/w->r/o transitions.
- */
- /*
+ * The warning here probably indicates that somebody messed
+ * up a mnt_want/drop_write() pair. If this happens, the
+ * filesystem was probably unable to make r/w->r/o transitions.
* The locking used to deal with mnt_count decrement provides barriers,
* so mnt_get_writers() below is safe.
*/
WARN_ON(mnt_get_writers(mnt));
if (unlikely(mnt->mnt_pins.first))
mnt_pin_kill(mnt);
+ hlist_for_each_entry_safe(m, p, &mnt->mnt_stuck_children, mnt_umount) {
+ hlist_del(&m->mnt_umount);
+ mntput(&m->mnt);
+ }
fsnotify_vfsmount_delete(&mnt->mnt);
dput(mnt->mnt.mnt_root);
deactivate_super(mnt->mnt.mnt_sb);
@@ -1160,6 +1156,7 @@ static void mntput_no_expire(struct mount *mnt)
struct mount *p, *tmp;
list_for_each_entry_safe(p, tmp, &mnt->mnt_mounts, mnt_child) {
umount_mnt(p, &list);
+ hlist_add_head(&p->mnt_umount, &mnt->mnt_stuck_children);
}
}
unlock_mount_hash();
@@ -1352,6 +1349,8 @@ EXPORT_SYMBOL(may_umount);
static void namespace_unlock(void)
{
struct hlist_head head;
+ struct hlist_node *p;
+ struct mount *m;
LIST_HEAD(list);

hlist_move_list(&unmounted, &head);
@@ -1366,7 +1365,10 @@ static void namespace_unlock(void)

synchronize_rcu_expedited();

- group_pin_kill(&head);
+ hlist_for_each_entry_safe(m, p, &head, mnt_umount) {
+ hlist_del(&m->mnt_umount);
+ mntput(&m->mnt);
+ }
}

static inline void namespace_lock(void)
@@ -1453,8 +1455,6 @@ static void umount_tree(struct mount *mnt, enum umount_tree_flags how)

disconnect = disconnect_mount(p, how);

- pin_insert_group(&p->mnt_umount, &p->mnt_parent->mnt,
- disconnect ? &unmounted : NULL);
if (mnt_has_parent(p)) {
mnt_add_count(p->mnt_parent, -1);
if (!disconnect) {
@@ -1462,6 +1462,7 @@ static void umount_tree(struct mount *mnt, enum umount_tree_flags how)
list_add_tail(&p->mnt_child, &p->mnt_parent->mnt_mounts);
} else {
umount_mnt(p, NULL);
+ hlist_add_head(&p->mnt_umount, &unmounted);
}
}
change_mnt_propagation(p, MS_PRIVATE);
@@ -1614,8 +1615,8 @@ void __detach_mounts(struct dentry *dentry)
while (!hlist_empty(&mp->m_list)) {
mnt = hlist_entry(mp->m_list.first, struct mount, mnt_mp_list);
if (mnt->mnt.mnt_flags & MNT_UMOUNT) {
- hlist_add_head(&mnt->mnt_umount.s_list, &unmounted);
umount_mnt(mnt, NULL);
+ hlist_add_head(&mnt->mnt_umount, &unmounted);
}
else umount_tree(mnt, UMOUNT_CONNECTED);
}
diff --git a/include/linux/fs_pin.h b/include/linux/fs_pin.h
index 7cab74d66f85..bdd09fd2520c 100644
--- a/include/linux/fs_pin.h
+++ b/include/linux/fs_pin.h
@@ -20,6 +20,5 @@ static inline void init_fs_pin(struct fs_pin *p, void (*kill)(struct fs_pin *))
}

void pin_remove(struct fs_pin *);
-void pin_insert_group(struct fs_pin *, struct vfsmount *, struct hlist_head *);
void pin_insert(struct fs_pin *, struct vfsmount *);
void pin_kill(struct fs_pin *);
--
2.11.0