[PATCH] count ghost references to vfsmounts

make propagate_mount_busy() exclude references from the vfsmounts
that had been isolated by umount_tree() and are just waiting for
release_mounts() to dispose of their ->mnt_parent/->mnt_mountpoint.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

3 files changed, 6 insertions, 2 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index 6324dfc80dc6..c175218ebae1 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -548,6 +548,7 @@ void release_mounts(struct list_head *head)
                         m = mnt->mnt_parent;
                         mnt->mnt_mountpoint = mnt->mnt_root;
                         mnt->mnt_parent = mnt;
+                        m->mnt_ghosts--;
                         spin_unlock(&vfsmount_lock);
                         dput(dentry);
                         mntput(m);
@@ -572,8 +573,10 @@ void umount_tree(struct vfsmount *mnt, int propagate, struct list_head *kill)
                 __touch_mnt_namespace(p->mnt_ns);
                 p->mnt_ns = NULL;
                 list_del_init(&p->mnt_child);
-                if (p->mnt_parent != p)
+                if (p->mnt_parent != p) {
+                        p->mnt_parent->mnt_ghosts++;
                         p->mnt_mountpoint->d_mounted--;
+                }
                 change_mnt_propagation(p, MS_PRIVATE);
         }
 }
diff --git a/fs/pnode.c b/fs/pnode.c
index 05ba692bc540..1d8f5447f3f7 100644
--- a/fs/pnode.c
+++ b/fs/pnode.c
@@ -225,7 +225,7 @@ out:
  */
 static inline int do_refcount_check(struct vfsmount *mnt, int count)
 {
-        int mycount = atomic_read(&mnt->mnt_count);
+        int mycount = atomic_read(&mnt->mnt_count) - mnt->mnt_ghosts;
         return (mycount > count);
 }
 
diff --git a/include/linux/mount.h b/include/linux/mount.h
index 6d3047d8c91c..dac5e67ff3ee 100644
--- a/include/linux/mount.h
+++ b/include/linux/mount.h
@@ -61,6 +61,7 @@ struct vfsmount {
         atomic_t mnt_count;
         int mnt_expiry_mark;            /* true if marked for expiry */
         int mnt_pinned;
+        int mnt_ghosts;
 };
 
 static inline struct vfsmount *mntget(struct vfsmount *mnt)