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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>
This commit is contained in:
Al Viro 2019-06-30 10:39:08 -04:00
parent 9bdebc2bd1
commit 4edbe133f8
2 changed files with 25 additions and 28 deletions
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1
fs/mount.h
View File

@ -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 */

52
fs/namespace.c
View File

@ -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;