On Tue, Sep 16, 2025 at 04:59:49AM +0100, Al Viro wrote:
On Tue, Sep 16, 2025 at 04:56:33AM +0100, Al Viro wrote:
if (!RB_EMPTY_NODE(to_ns_common(ns)->ns_tree_node))
if (!RB_EMPTY_NODE(&to_ns_common(ns)->ns_tree_node))
obviously...
FWIW, how about the following - I put the commit below into never-rebased branch, pull it into #work.mount and you do the same to your branch just prior to 18/33? The difference from one in #work.mount is that this variant checks RB_EMPTY_NODE(&ns->mnt_ns_tree_node) instead of list_empty(&ns->mnt_ns_list). The reasons why it's safe lockless are pretty much the same...
Objections? Does vfs/vfs.git #no-rebases-mnt_ns_tree_remove look sane for you?
mnt_ns_tree_remove(): DTRT if mnt_ns had never been added to mnt_ns_list
Actual removal is done under the lock, but for checking if need to bother the lockless RB_EMPTY_NODE() is safe - either that namespace had never been added to mnt_ns_tree, in which case the the node will stay empty, or whoever had allocated it has called mnt_ns_tree_add() and it has already run to completion. After that point RB_EMPTY_NODE() will become false and will remain false, no matter what we do with other nodes in the tree.
Signed-off-by: Al Viro viro@zeniv.linux.org.uk --- diff --git a/fs/namespace.c b/fs/namespace.c index ae6d1312b184..39afeb521a80 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -187,7 +187,7 @@ static void mnt_ns_release_rcu(struct rcu_head *rcu) static void mnt_ns_tree_remove(struct mnt_namespace *ns) { /* remove from global mount namespace list */ - if (!is_anon_ns(ns)) { + if (!RB_EMPTY_NODE(&ns->mnt_ns_tree_node)) { mnt_ns_tree_write_lock(); rb_erase(&ns->mnt_ns_tree_node, &mnt_ns_tree); list_bidir_del_rcu(&ns->mnt_ns_list);