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switch mnt_hash to hlist

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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>
This commit is contained in:
Al Viro
2014-03-20 21:10:51 -04:00
parent 0b1b901b5a
commit 38129a13e6
4 changed files with 61 additions and 50 deletions
Download Patch File Download Diff File Expand all files Collapse all files

26
fs/pnode.c
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@@ -220,14 +220,14 @@ static struct mount *get_source(struct mount *dest,
* @tree_list : list of heads of trees to be attached.
*/
int propagate_mnt(struct mount *dest_mnt, struct mountpoint *dest_mp,
struct mount *source_mnt, struct list_head *tree_list)
struct mount *source_mnt, struct hlist_head *tree_list)
{
struct user_namespace *user_ns = current->nsproxy->mnt_ns->user_ns;
struct mount *m, *child;
int ret = 0;
struct mount *prev_dest_mnt = dest_mnt;
struct mount *prev_src_mnt = source_mnt;
LIST_HEAD(tmp_list);
HLIST_HEAD(tmp_list);
for (m = propagation_next(dest_mnt, dest_mnt); m;
m = propagation_next(m, dest_mnt)) {
@@ -246,27 +246,29 @@ int propagate_mnt(struct mount *dest_mnt, struct mountpoint *dest_mp,
child = copy_tree(source, source->mnt.mnt_root, type);
if (IS_ERR(child)) {
ret = PTR_ERR(child);
list_splice(tree_list, tmp_list.prev);
tmp_list = *tree_list;
tmp_list.first->pprev = &tmp_list.first;
INIT_HLIST_HEAD(tree_list);
goto out;
}
if (is_subdir(dest_mp->m_dentry, m->mnt.mnt_root)) {
mnt_set_mountpoint(m, dest_mp, child);
list_add_tail(&child->mnt_hash, tree_list);
hlist_add_head(&child->mnt_hash, tree_list);
} else {
/*
* This can happen if the parent mount was bind mounted
* on some subdirectory of a shared/slave mount.
*/
list_add_tail(&child->mnt_hash, &tmp_list);
hlist_add_head(&child->mnt_hash, &tmp_list);
}
prev_dest_mnt = m;
prev_src_mnt = child;
}
out:
lock_mount_hash();
while (!list_empty(&tmp_list)) {
child = list_first_entry(&tmp_list, struct mount, mnt_hash);
while (!hlist_empty(&tmp_list)) {
child = hlist_entry(tmp_list.first, struct mount, mnt_hash);
umount_tree(child, 0);
}
unlock_mount_hash();
@@ -338,8 +340,10 @@ static void __propagate_umount(struct mount *mnt)
* umount the child only if the child has no
* other children
*/
if (child && list_empty(&child->mnt_mounts))
list_move_tail(&child->mnt_hash, &mnt->mnt_hash);
if (child && list_empty(&child->mnt_mounts)) {
hlist_del_init_rcu(&child->mnt_hash);
hlist_add_before_rcu(&child->mnt_hash, &mnt->mnt_hash);
}
}
}
@@ -350,11 +354,11 @@ static void __propagate_umount(struct mount *mnt)
*
* vfsmount lock must be held for write
*/
int propagate_umount(struct list_head *list)
int propagate_umount(struct hlist_head *list)
{
struct mount *mnt;
list_for_each_entry(mnt, list, mnt_hash)
hlist_for_each_entry(mnt, list, mnt_hash)
__propagate_umount(mnt);
return 0;
}