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mnt: Tuck mounts under others instead of creating shadow/side mounts.
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am: 808e83e

Change-Id: I58cb7df80b45193d209f697846c9fd0daa73e0a3
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@ebiederm
ebiederm authored and android-build-merger committed Mar 15, 2017
2 parents 29b9417 + 808e83e commit d4ffcb8
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Showing 4 changed files with 111 additions and 63 deletions.
1 change: 0 additions & 1 deletion fs/mount.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -89,7 +89,6 @@ static inline int is_mounted(struct vfsmount *mnt)
}

extern struct mount *__lookup_mnt(struct vfsmount *, struct dentry *);
extern struct mount *__lookup_mnt_last(struct vfsmount *, struct dentry *);

extern int __legitimize_mnt(struct vfsmount *, unsigned);
extern bool legitimize_mnt(struct vfsmount *, unsigned);
Expand Down
110 changes: 60 additions & 50 deletions fs/namespace.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -641,28 +641,6 @@ struct mount *__lookup_mnt(struct vfsmount *mnt, struct dentry *dentry)
return NULL;
}

/*
* find the last mount at @dentry on vfsmount @mnt.
* mount_lock must be held.
*/
struct mount *__lookup_mnt_last(struct vfsmount *mnt, struct dentry *dentry)
{
struct mount *p, *res = NULL;
p = __lookup_mnt(mnt, dentry);
if (!p)
goto out;
if (!(p->mnt.mnt_flags & MNT_UMOUNT))
res = p;
hlist_for_each_entry_continue(p, mnt_hash) {
if (&p->mnt_parent->mnt != mnt || p->mnt_mountpoint != dentry)
break;
if (!(p->mnt.mnt_flags & MNT_UMOUNT))
res = p;
}
out:
return res;
}

/*
* lookup_mnt - Return the first child mount mounted at path
*
Expand Down Expand Up @@ -883,6 +861,13 @@ void mnt_set_mountpoint(struct mount *mnt,
hlist_add_head(&child_mnt->mnt_mp_list, &mp->m_list);
}

static void __attach_mnt(struct mount *mnt, struct mount *parent)
{
hlist_add_head_rcu(&mnt->mnt_hash,
m_hash(&parent->mnt, mnt->mnt_mountpoint));
list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
}

/*
* vfsmount lock must be held for write
*/
Expand All @@ -891,28 +876,45 @@ static void attach_mnt(struct mount *mnt,
struct mountpoint *mp)
{
mnt_set_mountpoint(parent, mp, mnt);
hlist_add_head_rcu(&mnt->mnt_hash, m_hash(&parent->mnt, mp->m_dentry));
list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
__attach_mnt(mnt, parent);
}

static void attach_shadowed(struct mount *mnt,
struct mount *parent,
struct mount *shadows)
void mnt_change_mountpoint(struct mount *parent, struct mountpoint *mp, struct mount *mnt)
{
if (shadows) {
hlist_add_behind_rcu(&mnt->mnt_hash, &shadows->mnt_hash);
list_add(&mnt->mnt_child, &shadows->mnt_child);
} else {
hlist_add_head_rcu(&mnt->mnt_hash,
m_hash(&parent->mnt, mnt->mnt_mountpoint));
list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
}
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);
hlist_del_init(&mnt->mnt_mp_list);
hlist_del_init_rcu(&mnt->mnt_hash);

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);
}

/*
* vfsmount lock must be held for write
*/
static void commit_tree(struct mount *mnt, struct mount *shadows)
static void commit_tree(struct mount *mnt)
{
struct mount *parent = mnt->mnt_parent;
struct mount *m;
Expand All @@ -930,7 +932,7 @@ static void commit_tree(struct mount *mnt, struct mount *shadows)
n->mounts += n->pending_mounts;
n->pending_mounts = 0;

attach_shadowed(mnt, parent, shadows);
__attach_mnt(mnt, parent);
touch_mnt_namespace(n);
}

Expand Down Expand Up @@ -1757,7 +1759,6 @@ struct mount *copy_tree(struct mount *mnt, struct dentry *dentry,
continue;

for (s = r; s; s = next_mnt(s, r)) {
struct mount *t = NULL;
if (!(flag & CL_COPY_UNBINDABLE) &&
IS_MNT_UNBINDABLE(s)) {
s = skip_mnt_tree(s);
Expand All @@ -1779,14 +1780,7 @@ struct mount *copy_tree(struct mount *mnt, struct dentry *dentry,
goto out;
lock_mount_hash();
list_add_tail(&q->mnt_list, &res->mnt_list);
mnt_set_mountpoint(parent, p->mnt_mp, q);
if (!list_empty(&parent->mnt_mounts)) {
t = list_last_entry(&parent->mnt_mounts,
struct mount, mnt_child);
if (t->mnt_mp != p->mnt_mp)
t = NULL;
}
attach_shadowed(q, parent, t);
attach_mnt(q, parent, p->mnt_mp);
unlock_mount_hash();
}
}
Expand Down Expand Up @@ -1987,10 +1981,18 @@ static int attach_recursive_mnt(struct mount *source_mnt,
{
HLIST_HEAD(tree_list);
struct mnt_namespace *ns = dest_mnt->mnt_ns;
struct mountpoint *smp;
struct mount *child, *p;
struct hlist_node *n;
int err;

/* Preallocate a mountpoint in case the new mounts need
* to be tucked under other mounts.
*/
smp = get_mountpoint(source_mnt->mnt.mnt_root);
if (IS_ERR(smp))
return PTR_ERR(smp);

/* Is there space to add these mounts to the mount namespace? */
if (!parent_path) {
err = count_mounts(ns, source_mnt);
Expand All @@ -2017,16 +2019,19 @@ static int attach_recursive_mnt(struct mount *source_mnt,
touch_mnt_namespace(source_mnt->mnt_ns);
} else {
mnt_set_mountpoint(dest_mnt, dest_mp, source_mnt);
commit_tree(source_mnt, NULL);
commit_tree(source_mnt);
}

hlist_for_each_entry_safe(child, n, &tree_list, mnt_hash) {
struct mount *q;
hlist_del_init(&child->mnt_hash);
q = __lookup_mnt_last(&child->mnt_parent->mnt,
child->mnt_mountpoint);
commit_tree(child, q);
q = __lookup_mnt(&child->mnt_parent->mnt,
child->mnt_mountpoint);
if (q)
mnt_change_mountpoint(child, smp, q);
commit_tree(child);
}
put_mountpoint(smp);
unlock_mount_hash();

return 0;
Expand All @@ -2041,6 +2046,11 @@ static int attach_recursive_mnt(struct mount *source_mnt,
cleanup_group_ids(source_mnt, NULL);
out:
ns->pending_mounts = 0;

read_seqlock_excl(&mount_lock);
put_mountpoint(smp);
read_sequnlock_excl(&mount_lock);

return err;
}

Expand Down
61 changes: 49 additions & 12 deletions fs/pnode.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -324,6 +324,21 @@ int propagate_mnt(struct mount *dest_mnt, struct mountpoint *dest_mp,
return ret;
}

static struct mount *find_topper(struct mount *mnt)
{
/* If there is exactly one mount covering mnt completely return it. */
struct mount *child;

if (!list_is_singular(&mnt->mnt_mounts))
return NULL;

child = list_first_entry(&mnt->mnt_mounts, struct mount, mnt_child);
if (child->mnt_mountpoint != mnt->mnt.mnt_root)
return NULL;

return child;
}

/*
* return true if the refcount is greater than count
*/
Expand All @@ -344,9 +359,8 @@ static inline int do_refcount_check(struct mount *mnt, int count)
*/
int propagate_mount_busy(struct mount *mnt, int refcnt)
{
struct mount *m, *child;
struct mount *m, *child, *topper;
struct mount *parent = mnt->mnt_parent;
int ret = 0;

if (mnt == parent)
return do_refcount_check(mnt, refcnt);
Expand All @@ -361,12 +375,24 @@ int propagate_mount_busy(struct mount *mnt, int refcnt)

for (m = propagation_next(parent, parent); m;
m = propagation_next(m, parent)) {
child = __lookup_mnt_last(&m->mnt, mnt->mnt_mountpoint);
if (child && list_empty(&child->mnt_mounts) &&
(ret = do_refcount_check(child, 1)))
break;
int count = 1;
child = __lookup_mnt(&m->mnt, mnt->mnt_mountpoint);
if (!child)
continue;

/* Is there exactly one mount on the child that covers
* it completely whose reference should be ignored?
*/
topper = find_topper(child);
if (topper)
count += 1;
else if (!list_empty(&child->mnt_mounts))
continue;

if (do_refcount_check(child, count))
return 1;
}
return ret;
return 0;
}

/*
Expand All @@ -383,7 +409,7 @@ void propagate_mount_unlock(struct mount *mnt)

for (m = propagation_next(parent, parent); m;
m = propagation_next(m, parent)) {
child = __lookup_mnt_last(&m->mnt, mnt->mnt_mountpoint);
child = __lookup_mnt(&m->mnt, mnt->mnt_mountpoint);
if (child)
child->mnt.mnt_flags &= ~MNT_LOCKED;
}
Expand All @@ -401,9 +427,11 @@ static void mark_umount_candidates(struct mount *mnt)

for (m = propagation_next(parent, parent); m;
m = propagation_next(m, parent)) {
struct mount *child = __lookup_mnt_last(&m->mnt,
struct mount *child = __lookup_mnt(&m->mnt,
mnt->mnt_mountpoint);
if (child && (!IS_MNT_LOCKED(child) || IS_MNT_MARKED(m))) {
if (!child || (child->mnt.mnt_flags & MNT_UMOUNT))
continue;
if (!IS_MNT_LOCKED(child) || IS_MNT_MARKED(m)) {
SET_MNT_MARK(child);
}
}
Expand All @@ -422,8 +450,8 @@ static void __propagate_umount(struct mount *mnt)

for (m = propagation_next(parent, parent); m;
m = propagation_next(m, parent)) {

struct mount *child = __lookup_mnt_last(&m->mnt,
struct mount *topper;
struct mount *child = __lookup_mnt(&m->mnt,
mnt->mnt_mountpoint);
/*
* umount the child only if the child has no children
Expand All @@ -432,6 +460,15 @@ static void __propagate_umount(struct mount *mnt)
if (!child || !IS_MNT_MARKED(child))
continue;
CLEAR_MNT_MARK(child);

/* If there is exactly one mount covering all of child
* replace child with that mount.
*/
topper = find_topper(child);
if (topper)
mnt_change_mountpoint(child->mnt_parent, child->mnt_mp,
topper);

if (list_empty(&child->mnt_mounts)) {
list_del_init(&child->mnt_child);
child->mnt.mnt_flags |= MNT_UMOUNT;
Expand Down
2 changes: 2 additions & 0 deletions fs/pnode.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -50,6 +50,8 @@ int get_dominating_id(struct mount *mnt, const struct path *root);
unsigned int mnt_get_count(struct mount *mnt);
void mnt_set_mountpoint(struct mount *, struct mountpoint *,
struct mount *);
void mnt_change_mountpoint(struct mount *parent, struct mountpoint *mp,
struct mount *mnt);
struct mount *copy_tree(struct mount *, struct dentry *, int);
bool is_path_reachable(struct mount *, struct dentry *,
const struct path *root);
Expand Down

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