Kill CL_PROPAGATION, sanitize fs/pnode.c:get_source()

First of all, get_source() never results in CL_PROPAGATION
alone.  We either get CL_MAKE_SHARED (for the continuation
of peer group) or CL_SLAVE (slave that is not shared) or both
(beginning of peer group among slaves).  Massage the code to
make that explicit, kill CL_PROPAGATION test in clone_mnt()
(nothing sets CL_MAKE_SHARED without CL_PROPAGATION and in
clone_mnt() we are checking CL_PROPAGATION after we'd found
that there's no CL_SLAVE, so the check for CL_MAKE_SHARED
would do just as well).

Fix comments, while we are at it...

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

3 files changed, 19 insertions, 14 deletions

diff --git a/fs/namespace.c b/fs/namespace.c
index c768f733c8d6..25c1dcf9e9eb 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -573,7 +573,7 @@ static struct vfsmount *clone_mnt(struct vfsmount *old, struct dentry *root,
                         mnt->mnt_master = old;
                         CLEAR_MNT_SHARED(mnt);
                 } else if (!(flag & CL_PRIVATE)) {
-                        if ((flag & CL_PROPAGATION) || IS_MNT_SHARED(old))
+                        if ((flag & CL_MAKE_SHARED) || IS_MNT_SHARED(old))
                                 list_add(&mnt->mnt_share, &old->mnt_share);
                         if (IS_MNT_SLAVE(old))
                                 list_add(&mnt->mnt_slave, &old->mnt_slave);
diff --git a/fs/pnode.c b/fs/pnode.c
index 8d5f392ec3d3..5cc564a83149 100644
--- a/fs/pnode.c
+++ b/fs/pnode.c
@@ -86,7 +86,7 @@ static int do_make_slave(struct vfsmount *mnt)
 
         /*
          * slave 'mnt' to a peer mount that has the
-         * same root dentry. If none is available than
+         * same root dentry. If none is available then
          * slave it to anything that is available.
          */
         while ((peer_mnt = next_peer(peer_mnt)) != mnt &&
@@ -147,6 +147,11 @@ void change_mnt_propagation(struct vfsmount *mnt, int type)
  * get the next mount in the propagation tree.
  * @m: the mount seen last
  * @origin: the original mount from where the tree walk initiated
+ *
+ * Note that peer groups form contiguous segments of slave lists.
+ * We rely on that in get_source() to be able to find out if
+ * vfsmount found while iterating with propagation_next() is
+ * a peer of one we'd found earlier.
  */
 static struct vfsmount *propagation_next(struct vfsmount *m,
                                          struct vfsmount *origin)
@@ -186,10 +191,6 @@ static struct vfsmount *get_source(struct vfsmount *dest,
 {
         struct vfsmount *p_last_src = NULL;
         struct vfsmount *p_last_dest = NULL;
-        *type = CL_PROPAGATION;
-
-        if (IS_MNT_SHARED(dest))
-                *type |= CL_MAKE_SHARED;
 
         while (last_dest != dest->mnt_master) {
                 p_last_dest = last_dest;
@@ -202,13 +203,18 @@ static struct vfsmount *get_source(struct vfsmount *dest,
                 do {
                         p_last_dest = next_peer(p_last_dest);
                 } while (IS_MNT_NEW(p_last_dest));
+                /* is that a peer of the earlier? */
+                if (dest == p_last_dest) {
+                        *type = CL_MAKE_SHARED;
+                        return p_last_src;
+                }
         }
-
-        if (dest != p_last_dest) {
-                *type |= CL_SLAVE;
-                return last_src;
-        } else
-                return p_last_src;
+        /* slave of the earlier, then */
+        *type = CL_SLAVE;
+        /* beginning of peer group among the slaves? */
+        if (IS_MNT_SHARED(dest))
+                *type |= CL_MAKE_SHARED;
+        return last_src;
 }
 
 /*
diff --git a/fs/pnode.h b/fs/pnode.h
index 958665d662af..6c7ef3252a26 100644
--- a/fs/pnode.h
+++ b/fs/pnode.h
@@ -21,8 +21,7 @@
 #define CL_SLAVE                0x02
 #define CL_COPY_ALL             0x04
 #define CL_MAKE_SHARED          0x08
-#define CL_PROPAGATION          0x10
-#define CL_PRIVATE              0x20
+#define CL_PRIVATE              0x10
 
 static inline void set_mnt_shared(struct vfsmount *mnt)
 {