switch mnt_hash to hlist
fixes RCU bug - walking through hlist is safe in face of element moves,
since it's self-terminating. Cyclic lists are not - if we end up jumping
to another hash chain, we'll loop infinitely without ever hitting the
original list head.
[fix for dumb braino folded]
Spotted by: Max Kellermann <mk@cm4all.com>
Cc: stable@vger.kernel.org
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/namespace.c b/fs/namespace.c
index d3fb9f0..2ffc5a2 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -59,7 +59,7 @@
static int mnt_id_start = 0;
static int mnt_group_start = 1;
-static struct list_head *mount_hashtable __read_mostly;
+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);
@@ -78,7 +78,7 @@
*/
__cacheline_aligned_in_smp DEFINE_SEQLOCK(mount_lock);
-static inline struct list_head *m_hash(struct vfsmount *mnt, struct dentry *dentry)
+static inline struct hlist_head *m_hash(struct vfsmount *mnt, struct dentry *dentry)
{
unsigned long tmp = ((unsigned long)mnt / L1_CACHE_BYTES);
tmp += ((unsigned long)dentry / L1_CACHE_BYTES);
@@ -217,7 +217,7 @@
mnt->mnt_writers = 0;
#endif
- INIT_LIST_HEAD(&mnt->mnt_hash);
+ INIT_HLIST_NODE(&mnt->mnt_hash);
INIT_LIST_HEAD(&mnt->mnt_child);
INIT_LIST_HEAD(&mnt->mnt_mounts);
INIT_LIST_HEAD(&mnt->mnt_list);
@@ -605,10 +605,10 @@
*/
struct mount *__lookup_mnt(struct vfsmount *mnt, struct dentry *dentry)
{
- struct list_head *head = m_hash(mnt, dentry);
+ struct hlist_head *head = m_hash(mnt, dentry);
struct mount *p;
- list_for_each_entry_rcu(p, head, mnt_hash)
+ hlist_for_each_entry_rcu(p, head, mnt_hash)
if (&p->mnt_parent->mnt == mnt && p->mnt_mountpoint == dentry)
return p;
return NULL;
@@ -620,20 +620,16 @@
*/
struct mount *__lookup_mnt_last(struct vfsmount *mnt, struct dentry *dentry)
{
- struct list_head *head = m_hash(mnt, dentry);
- struct mount *p, *res = NULL;
-
- list_for_each_entry(p, head, mnt_hash)
- if (&p->mnt_parent->mnt == mnt && p->mnt_mountpoint == dentry)
- goto found;
- return res;
-found:
- res = p;
- list_for_each_entry_continue(p, head, mnt_hash) {
+ struct mount *p, *res;
+ res = p = __lookup_mnt(mnt, dentry);
+ if (!p)
+ goto out;
+ hlist_for_each_entry_continue(p, mnt_hash) {
if (&p->mnt_parent->mnt != mnt || p->mnt_mountpoint != dentry)
break;
res = p;
}
+out:
return res;
}
@@ -750,7 +746,7 @@
mnt->mnt_parent = mnt;
mnt->mnt_mountpoint = mnt->mnt.mnt_root;
list_del_init(&mnt->mnt_child);
- list_del_init(&mnt->mnt_hash);
+ hlist_del_init_rcu(&mnt->mnt_hash);
put_mountpoint(mnt->mnt_mp);
mnt->mnt_mp = NULL;
}
@@ -777,7 +773,7 @@
struct mountpoint *mp)
{
mnt_set_mountpoint(parent, mp, mnt);
- list_add(&mnt->mnt_hash, m_hash(&parent->mnt, mp->m_dentry));
+ hlist_add_head_rcu(&mnt->mnt_hash, m_hash(&parent->mnt, mp->m_dentry));
list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
}
@@ -800,9 +796,9 @@
list_splice(&head, n->list.prev);
if (shadows)
- list_add(&mnt->mnt_hash, &shadows->mnt_hash);
+ hlist_add_after_rcu(&shadows->mnt_hash, &mnt->mnt_hash);
else
- list_add(&mnt->mnt_hash,
+ hlist_add_head_rcu(&mnt->mnt_hash,
m_hash(&parent->mnt, mnt->mnt_mountpoint));
list_add_tail(&mnt->mnt_child, &parent->mnt_mounts);
touch_mnt_namespace(n);
@@ -1193,26 +1189,28 @@
EXPORT_SYMBOL(may_umount);
-static LIST_HEAD(unmounted); /* protected by namespace_sem */
+static HLIST_HEAD(unmounted); /* protected by namespace_sem */
static void namespace_unlock(void)
{
struct mount *mnt;
- LIST_HEAD(head);
+ struct hlist_head head = unmounted;
- if (likely(list_empty(&unmounted))) {
+ if (likely(hlist_empty(&head))) {
up_write(&namespace_sem);
return;
}
- list_splice_init(&unmounted, &head);
+ head.first->pprev = &head.first;
+ INIT_HLIST_HEAD(&unmounted);
+
up_write(&namespace_sem);
synchronize_rcu();
- while (!list_empty(&head)) {
- mnt = list_first_entry(&head, struct mount, mnt_hash);
- list_del_init(&mnt->mnt_hash);
+ while (!hlist_empty(&head)) {
+ mnt = hlist_entry(head.first, struct mount, mnt_hash);
+ hlist_del_init(&mnt->mnt_hash);
if (mnt->mnt_ex_mountpoint.mnt)
path_put(&mnt->mnt_ex_mountpoint);
mntput(&mnt->mnt);
@@ -1233,16 +1231,19 @@
*/
void umount_tree(struct mount *mnt, int how)
{
- LIST_HEAD(tmp_list);
+ HLIST_HEAD(tmp_list);
struct mount *p;
+ struct mount *last = NULL;
- for (p = mnt; p; p = next_mnt(p, mnt))
- list_move(&p->mnt_hash, &tmp_list);
+ for (p = mnt; p; p = next_mnt(p, mnt)) {
+ hlist_del_init_rcu(&p->mnt_hash);
+ hlist_add_head(&p->mnt_hash, &tmp_list);
+ }
if (how)
propagate_umount(&tmp_list);
- list_for_each_entry(p, &tmp_list, mnt_hash) {
+ hlist_for_each_entry(p, &tmp_list, mnt_hash) {
list_del_init(&p->mnt_expire);
list_del_init(&p->mnt_list);
__touch_mnt_namespace(p->mnt_ns);
@@ -1260,8 +1261,13 @@
p->mnt_mp = NULL;
}
change_mnt_propagation(p, MS_PRIVATE);
+ last = p;
}
- list_splice(&tmp_list, &unmounted);
+ if (last) {
+ last->mnt_hash.next = unmounted.first;
+ unmounted.first = tmp_list.first;
+ unmounted.first->pprev = &unmounted.first;
+ }
}
static void shrink_submounts(struct mount *mnt);
@@ -1645,8 +1651,9 @@
struct mountpoint *dest_mp,
struct path *parent_path)
{
- LIST_HEAD(tree_list);
+ HLIST_HEAD(tree_list);
struct mount *child, *p;
+ struct hlist_node *n;
int err;
if (IS_MNT_SHARED(dest_mnt)) {
@@ -1671,9 +1678,9 @@
commit_tree(source_mnt, NULL);
}
- list_for_each_entry_safe(child, p, &tree_list, mnt_hash) {
+ hlist_for_each_entry_safe(child, n, &tree_list, mnt_hash) {
struct mount *q;
- list_del_init(&child->mnt_hash);
+ hlist_del_init(&child->mnt_hash);
q = __lookup_mnt_last(&child->mnt_parent->mnt,
child->mnt_mountpoint);
commit_tree(child, q);
@@ -2818,7 +2825,7 @@
0, SLAB_HWCACHE_ALIGN | SLAB_PANIC, NULL);
mount_hashtable = alloc_large_system_hash("Mount-cache",
- sizeof(struct list_head),
+ sizeof(struct hlist_head),
mhash_entries, 19,
0,
&m_hash_shift, &m_hash_mask, 0, 0);
@@ -2832,7 +2839,7 @@
panic("Failed to allocate mount hash table\n");
for (u = 0; u <= m_hash_mask; u++)
- INIT_LIST_HEAD(&mount_hashtable[u]);
+ INIT_HLIST_HEAD(&mount_hashtable[u]);
for (u = 0; u <= mp_hash_mask; u++)
INIT_HLIST_HEAD(&mountpoint_hashtable[u]);