[PATCH 4/6] make struct mountpoint bear the dentry reference to mountpoint, not struct mount

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

fs/mount.h | 1 -
fs/namespace.c | 66 +++++++++++++++++++++++++---------------------------------
2 files changed, 28 insertions(+), 39 deletions(-)

diff --git a/fs/mount.h b/fs/mount.h
index 6250de544760..84aa8cdf4971 100644
--- a/fs/mount.h
+++ b/fs/mount.h
@@ -69,7 +69,6 @@ struct mount {
int mnt_expiry_mark; /* true if marked for expiry */
struct hlist_head mnt_pins;
struct fs_pin mnt_umount;
- struct dentry *mnt_ex_mountpoint;
} __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 b7059a4f07e3..911675de2a70 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);

/* /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 +753,7 @@ static struct mountpoint *get_mountpoint(struct dentry *dentry)
return mp;
}

-static void put_mountpoint(struct mountpoint *mp)
+static void put_mountpoint(struct mountpoint *mp, struct list_head *list)
{
if (!--mp->m_count) {
struct dentry *dentry = mp->m_dentry;
@@ -760,6 +761,9 @@ static void put_mountpoint(struct mountpoint *mp)
spin_lock(&dentry->d_lock);
dentry->d_flags &= ~DCACHE_MOUNTED;
spin_unlock(&dentry->d_lock);
+ if (!list)
+ list = &ex_mountpoints;
+ dput_to_list(dentry, list);
hlist_del(&mp->m_hash);
kfree(mp);
}
@@ -813,19 +817,17 @@ 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));
+ put_mountpoint(unhash_mnt(mnt), NULL);
}

/*
* vfsmount lock must be held for write
*/
-static void umount_mnt(struct mount *mnt)
+static void umount_mnt(struct mount *mnt, struct list_head *list)
{
- /* old mountpoint will be dropped when we can do that */
- mnt->mnt_ex_mountpoint = mnt->mnt_mountpoint;
- put_mountpoint(unhash_mnt(mnt));
+ put_mountpoint(unhash_mnt(mnt), list);
}

/*
@@ -837,7 +839,7 @@ 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 +866,6 @@ 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);
@@ -873,23 +874,7 @@ 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);
-
+ put_mountpoint(old_mp, NULL);
mnt_add_count(old_parent, -1);
}

@@ -1142,6 +1127,8 @@ 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 +1169,11 @@ 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);
+ umount_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 +1359,18 @@ 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;

@@ -1481,7 +1471,7 @@ static void umount_tree(struct mount *mnt, enum umount_tree_flags how)
/* Don't forget about p */
list_add_tail(&p->mnt_child, &p->mnt_parent->mnt_mounts);
} else {
- umount_mnt(p);
+ umount_mnt(p, NULL);
}
}
change_mnt_propagation(p, MS_PRIVATE);
@@ -1635,11 +1625,11 @@ void __detach_mounts(struct dentry *dentry)
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);
+ umount_mnt(mnt, NULL);
}
else umount_tree(mnt, UMOUNT_CONNECTED);
}
- put_mountpoint(mp);
+ put_mountpoint(mp, NULL);
out_unlock:
unlock_mount_hash();
namespace_unlock();
@@ -2110,7 +2100,7 @@ static int attach_recursive_mnt(struct mount *source_mnt,
child->mnt.mnt_flags &= ~MNT_LOCKED;
commit_tree(child);
}
- put_mountpoint(smp);
+ put_mountpoint(smp, NULL);
unlock_mount_hash();

return 0;
@@ -2127,7 +2117,7 @@ static int attach_recursive_mnt(struct mount *source_mnt,
ns->pending_mounts = 0;

read_seqlock_excl(&mount_lock);
- put_mountpoint(smp);
+ put_mountpoint(smp, NULL);
read_sequnlock_excl(&mount_lock);

return err;
@@ -2167,7 +2157,7 @@ static void unlock_mount(struct mountpoint *where)
struct dentry *dentry = where->m_dentry;

read_seqlock_excl(&mount_lock);
- put_mountpoint(where);
+ put_mountpoint(where, NULL);
read_sequnlock_excl(&mount_lock);

namespace_unlock();
@@ -3663,7 +3653,7 @@ SYSCALL_DEFINE2(pivot_root, const char __user *, new_root,
touch_mnt_namespace(current->nsproxy->mnt_ns);
/* A moved mount should not expire automatically */
list_del_init(&new_mnt->mnt_expire);
- put_mountpoint(root_mp);
+ put_mountpoint(root_mp, NULL);
unlock_mount_hash();
chroot_fs_refs(&root, &new);
error = 0;
--
2.11.0