Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs

Pull vfs fixes from Al Viro:

 - backport-friendly part of lock_parent() race fix

 - a fix for an assumption in the heurisic used by path_connected() that
   is not true on NFS

 - livelock fixes for d_alloc_parallel()

* 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs:
  fs: Teach path_connected to handle nfs filesystems with multiple roots.
  fs: dcache: Use READ_ONCE when accessing i_dir_seq
  fs: dcache: Avoid livelock between d_alloc_parallel and __d_add
  lock_parent() needs to recheck if dentry got __dentry_kill'ed under it

3 files changed, 21 insertions, 7 deletions

diff --git a/fs/dcache.c b/fs/dcache.c
index 7c38f39958bc..8945e6cabd93 100644
--- a/fs/dcache.c
+++ b/fs/dcache.c
@@ -647,11 +647,16 @@ again:
                 spin_unlock(&parent->d_lock);
                 goto again;
         }
-        rcu_read_unlock();
-        if (parent != dentry)
+        if (parent != dentry) {
                 spin_lock_nested(&dentry->d_lock, DENTRY_D_LOCK_NESTED);
-        else
+                if (unlikely(dentry->d_lockref.count < 0)) {
+                        spin_unlock(&parent->d_lock);
+                        parent = NULL;
+                }
+        } else {
                 parent = NULL;
+        }
+        rcu_read_unlock();
         return parent;
 }
 
@@ -2474,7 +2479,7 @@ struct dentry *d_alloc_parallel(struct dentry *parent,
 
 retry:
         rcu_read_lock();
-        seq = smp_load_acquire(&parent->d_inode->i_dir_seq) & ~1;
+        seq = smp_load_acquire(&parent->d_inode->i_dir_seq);
         r_seq = read_seqbegin(&rename_lock);
         dentry = __d_lookup_rcu(parent, name, &d_seq);
         if (unlikely(dentry)) {
@@ -2495,8 +2500,14 @@ retry:
                 rcu_read_unlock();
                 goto retry;
         }
+
+        if (unlikely(seq & 1)) {
+                rcu_read_unlock();
+                goto retry;
+        }
+
         hlist_bl_lock(b);
-        if (unlikely(parent->d_inode->i_dir_seq != seq)) {
+        if (unlikely(READ_ONCE(parent->d_inode->i_dir_seq) != seq)) {
                 hlist_bl_unlock(b);
                 rcu_read_unlock();
                 goto retry;
diff --git a/fs/namei.c b/fs/namei.c
index 921ae32dbc80..cafa365eeb70 100644
--- a/fs/namei.c
+++ b/fs/namei.c
@@ -559,9 +559,10 @@ static int __nd_alloc_stack(struct nameidata *nd)
 static bool path_connected(const struct path *path)
 {
         struct vfsmount *mnt = path->mnt;
+        struct super_block *sb = mnt->mnt_sb;
 
-        /* Only bind mounts can have disconnected paths */
-        if (mnt->mnt_root == mnt->mnt_sb->s_root)
+        /* Bind mounts and multi-root filesystems can have disconnected paths */
+        if (!(sb->s_iflags & SB_I_MULTIROOT) && (mnt->mnt_root == sb->s_root))
                 return true;
 
         return is_subdir(path->dentry, mnt->mnt_root);
diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index 29bacdc56f6a..5e470e233c83 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -2631,6 +2631,8 @@ struct dentry *nfs_fs_mount_common(struct nfs_server *server,
                 /* initial superblock/root creation */
                 mount_info->fill_super(s, mount_info);
                 nfs_get_cache_cookie(s, mount_info->parsed, mount_info->cloned);
+                if (!(server->flags & NFS_MOUNT_UNSHARED))
+                        s->s_iflags |= SB_I_MULTIROOT;
         }
 
         mntroot = nfs_get_root(s, mount_info->mntfh, dev_name);