From: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
This patch does NOT apply to the 3.12 stable tree. If you still want
it applied, please provide a backport.
===============
commit 81b6b06197606b4bef4e427a197aeb808e8d89e1 upstream.
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@xxxxxxxxxxxxxxx # 3.12+
Signed-off-by: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
---
fs/namespace.c | 6 ++++++
1 file changed, 6 insertions(+)
diff --git a/fs/namespace.c b/fs/namespace.c
index 3273177873f0..ef42d9bee212 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;
--
2.1.0
--
To unsubscribe from this list: send the line "unsubscribe stable" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html