[PATCH 21/53] afs: use d_splice_alias() in afs_vnode_new_inode()

[NeilBrown]

From: NeilBrown <neil at brown.name>

As afs supports the fhandle interfaces there is a theoretical possibility
that the inode created for mkdir could be found by open_by_handle_at()
and given a dentry before d_instantiate() is called.  This would result
in two dentries for the one directory inode, which is not permitted.

So this patch changes afs_mkdir() to use d_splice_alias() and to
return the alternate dentry from ->mkdir() if appropriate.

Signed-off-by: NeilBrown <neil at brown.name>
---
 fs/afs/dir.c      | 14 ++++++++++----
 fs/afs/internal.h |  1 +
 2 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/fs/afs/dir.c b/fs/afs/dir.c
index 9c57614feccf..1e472768e1f1 100644
--- a/fs/afs/dir.c
+++ b/fs/afs/dir.c
@@ -1248,7 +1248,7 @@ void afs_check_for_remote_deletion(struct afs_operation *op)
 /*
  * Create a new inode for create/mkdir/symlink
  */
-static void afs_vnode_new_inode(struct afs_operation *op)
+static struct dentry *afs_vnode_new_inode(struct afs_operation *op)
 {
 	struct afs_vnode_param *dvp = &op->file[0];
 	struct afs_vnode_param *vp = &op->file[1];
@@ -1265,7 +1265,7 @@ static void afs_vnode_new_inode(struct afs_operation *op)
 		 * the new directory on the server.
 		 */
 		afs_op_accumulate_error(op, PTR_ERR(inode), 0);
-		return;
+		return NULL;
 	}
 
 	vnode = AFS_FS_I(inode);
@@ -1276,7 +1276,7 @@ static void afs_vnode_new_inode(struct afs_operation *op)
 		afs_init_new_symlink(vnode, op);
 	if (!afs_op_error(op))
 		afs_cache_permit(vnode, op->key, vnode->cb_break, &vp->scb);
-	d_instantiate(op->dentry, inode);
+	return d_splice_alias(inode, op->dentry);
 }
 
 static void afs_create_success(struct afs_operation *op)
@@ -1285,7 +1285,7 @@ static void afs_create_success(struct afs_operation *op)
 	op->ctime = op->file[0].scb.status.mtime_client;
 	afs_vnode_commit_status(op, &op->file[0]);
 	afs_update_dentry_version(op, &op->file[0], op->dentry);
-	afs_vnode_new_inode(op);
+	op->create.ret = afs_vnode_new_inode(op);
 }
 
 static void afs_create_edit_dir(struct afs_operation *op)
@@ -1356,6 +1356,12 @@ static struct dentry *afs_mkdir(struct mnt_idmap *idmap, struct inode *dir,
 	op->ops		= &afs_mkdir_operation;
 	ret = afs_do_sync_operation(op);
 	afs_dir_unuse_cookie(dvnode, ret);
+	if (op->create.ret) {
+		/* Alternate dentry */
+		if (ret == 0)
+			return op->create.ret;
+		dput(op->create.ret);
+	}
 	return ERR_PTR(ret);
 }
 
diff --git a/fs/afs/internal.h b/fs/afs/internal.h
index f2898ce9c0e6..ce94f10a14c0 100644
--- a/fs/afs/internal.h
+++ b/fs/afs/internal.h
@@ -889,6 +889,7 @@ struct afs_operation {
 			int	reason;		/* enum afs_edit_dir_reason */
 			mode_t	mode;
 			const char *symlink;
+			struct dentry *ret;
 		} create;
 		struct {
 			struct dentry	*unblock;
-- 
2.50.0.107.gf914562f5916.dirty