From b7e1da5a62caa4191e5ef1e9178da66a051127b2 Mon Sep 17 00:00:00 2001 From: Al Viro Date: Sat, 30 Aug 2014 18:32:05 -0400 Subject: [PATCH] fix EBUSY on umount() from MNT_SHRINKABLE We need the parents of victims alive until namespace_unlock() gets to dput() of the (ex-)mountpoints. However, that screws up the "is it busy" checks in case when we have shrinkable mounts that need to be killed. Solution: go ahead and decrement refcounts of parents right in umount_tree(), increment them again just before dropping rwsem in namespace_unlock() (and let the loop in the end of namespace_unlock() finally drop those references for good, as we do now). Parents can't get freed until we drop rwsem - at least one reference is kept until then, both in case when parent is among the victims and when it is not. So they'll still be around when we get to namespace_unlock(). Cc: stable@vger.kernel.org # 3.12+ Signed-off-by: Al Viro --- fs/namespace.c | 6 ++++++ 1 file changed, 6 insertions(+) diff --git a/fs/namespace.c b/fs/namespace.c index 3273177873f0a..ef42d9bee2121 100644 --- a/fs/namespace.c +++ b/fs/namespace.c @@ -1217,6 +1217,11 @@ static void namespace_unlock(void) head.first->pprev = &head.first; INIT_HLIST_HEAD(&unmounted); + /* undo decrements we'd done in umount_tree() */ + hlist_for_each_entry(mnt, &head, mnt_hash) + if (mnt->mnt_ex_mountpoint.mnt) + mntget(mnt->mnt_ex_mountpoint.mnt); + up_write(&namespace_sem); synchronize_rcu(); @@ -1268,6 +1273,7 @@ void umount_tree(struct mount *mnt, int how) p->mnt.mnt_flags |= MNT_SYNC_UMOUNT; if (mnt_has_parent(p)) { put_mountpoint(p->mnt_mp); + mnt_add_count(p->mnt_parent, -1); /* move the reference to mountpoint into ->mnt_ex_mountpoint */ p->mnt_ex_mountpoint.dentry = p->mnt_mountpoint; p->mnt_ex_mountpoint.mnt = &p->mnt_parent->mnt; -- 2.39.5