massage __follow_mount_rcu() a bit

make the loop more similar to that in follow_managed(), with
explicit tracking of flags, etc.

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

diff --git a/fs/namei.c b/fs/namei.c
index b45ec86..18c46b8 100644 (file)
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -1269,12 +1269,6 @@ int follow_down_one(struct path *path)
 }
 EXPORT_SYMBOL(follow_down_one);
 
-static inline int managed_dentry_rcu(const struct path *path)
-{
-       return (path->dentry->d_flags & DCACHE_MANAGE_TRANSIT) ?
-               path->dentry->d_op->d_manage(path, true) : 0;
-}
-
 /*
  * Try to skip to top of mountpoint pile in rcuwalk mode.  Fail if
  * we meet a managed dentry that would need blocking.
@@ -1282,43 +1276,49 @@ static inline int managed_dentry_rcu(const struct path *path)
 static bool __follow_mount_rcu(struct nameidata *nd, struct path *path,
                               struct inode **inode, unsigned *seqp)
 {
+       struct dentry *dentry = path->dentry;
+       unsigned int flags = dentry->d_flags;
+
+       if (likely(!(flags & DCACHE_MANAGED_DENTRY)))
+               return true;
+
+       if (unlikely(nd->flags & LOOKUP_NO_XDEV))
+               return false;
+
        for (;;) {
-               struct mount *mounted;
                /*
                 * Don't forget we might have a non-mountpoint managed dentry
                 * that wants to block transit.
                 */
-               switch (managed_dentry_rcu(path)) {
-               case -ECHILD:
-               default:
-                       return false;
-               case -EISDIR:
-                       return true;
-               case 0:
-                       break;
+               if (unlikely(flags & DCACHE_MANAGE_TRANSIT)) {
+                       int res = dentry->d_op->d_manage(path, true);
+                       if (res)
+                               return res == -EISDIR;
+                       flags = dentry->d_flags;
                }
 
-               if (!d_mountpoint(path->dentry))
-                       return !(path->dentry->d_flags & DCACHE_NEED_AUTOMOUNT);
-
-               mounted = __lookup_mnt(path->mnt, path->dentry);
-               if (!mounted)
-                       break;
-               if (unlikely(nd->flags & LOOKUP_NO_XDEV))
-                       return false;
-               path->mnt = &mounted->mnt;
-               path->dentry = mounted->mnt.mnt_root;
-               nd->flags |= LOOKUP_JUMPED;
-               *seqp = read_seqcount_begin(&path->dentry->d_seq);
-               /*
-                * Update the inode too. We don't need to re-check the
-                * dentry sequence number here after this d_inode read,
-                * because a mount-point is always pinned.
-                */
-               *inode = path->dentry->d_inode;
+               if (flags & DCACHE_MOUNTED) {
+                       struct mount *mounted = __lookup_mnt(path->mnt, dentry);
+                       if (mounted) {
+                               path->mnt = &mounted->mnt;
+                               dentry = path->dentry = mounted->mnt.mnt_root;
+                               nd->flags |= LOOKUP_JUMPED;
+                               *seqp = read_seqcount_begin(&dentry->d_seq);
+                               *inode = dentry->d_inode;
+                               /*
+                                * We don't need to re-check ->d_seq after this
+                                * ->d_inode read - there will be an RCU delay
+                                * between mount hash removal and ->mnt_root
+                                * becoming unpinned.
+                                */
+                               flags = dentry->d_flags;
+                               continue;
+                       }
+                       if (read_seqretry(&mount_lock, nd->m_seq))
+                               return false;
+               }
+               return !(flags & DCACHE_NEED_AUTOMOUNT);
        }
-       return !read_seqretry(&mount_lock, nd->m_seq) &&
-               !(path->dentry->d_flags & DCACHE_NEED_AUTOMOUNT);
 }
 
 static inline int handle_mounts(struct nameidata *nd, struct dentry *dentry,