[PATCH 01/20] ovl: simplify an error path in ovl_copy_up_workdir()

[NeilBrown <neil@brown.name>]

If ovl_copy_up_data() fails the error is not immediately handled but the
code continues on to call ovl_start_write() and lock_rename(),
presumably because both of these locks are needed for the cleanup.
On then (if the lock was successful) is the error checked.

This makes the code a little hard to follow and could be fragile.

This patch changes to handle the error immediately.  A new
ovl_cleanup_unlocked() is created which takes the required directory
lock (though it doesn't take the write lock on the filesystem).  This
will be used extensively in later patches.

In general we need to check the parent is still correct after taking the
lock (as ovl_copy_up_workdir() does after a successful lock_rename()) so
that is included in ovl_cleanup_unlocked() using new lock_parent() and
unlock_parent() calls (it is planned to move this API into VFS code
eventually, though in a slightly different form).

A fresh cleanup block is added which doesn't share code with other
cleanup blocks.  It will get a new users in the next patch.

Signed-off-by: NeilBrown <neil@brown.name>
---
 fs/overlayfs/copy_up.c   | 12 ++++++++++--
 fs/overlayfs/dir.c       | 15 +++++++++++++++
 fs/overlayfs/overlayfs.h |  6 ++++++
 fs/overlayfs/util.c      | 10 ++++++++++
 4 files changed, 41 insertions(+), 2 deletions(-)

diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index 8a3c0d18ec2e..5d21b8d94a0a 100644
--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -794,6 +794,9 @@ static int ovl_copy_up_workdir(struct ovl_copy_up_ctx *c)
 	 */
 	path.dentry = temp;
 	err = ovl_copy_up_data(c, &path);
+	if (err)
+		goto cleanup_need_write;
+
 	/*
 	 * We cannot hold lock_rename() throughout this helper, because of
 	 * lock ordering with sb_writers, which shouldn't be held when calling
@@ -809,8 +812,6 @@ static int ovl_copy_up_workdir(struct ovl_copy_up_ctx *c)
 		if (IS_ERR(trap))
 			goto out;
 		goto unlock;
-	} else if (err) {
-		goto cleanup;
 	}
 
 	err = ovl_copy_up_metadata(c, temp);
@@ -857,6 +858,13 @@ static int ovl_copy_up_workdir(struct ovl_copy_up_ctx *c)
 	ovl_cleanup(ofs, wdir, temp);
 	dput(temp);
 	goto unlock;
+
+cleanup_need_write:
+	ovl_start_write(c->dentry);
+	ovl_cleanup_unlocked(ofs, c->workdir, temp);
+	ovl_end_write(c->dentry);
+	dput(temp);
+	return err;
 }
 
 /* Copyup using O_TMPFILE which does not require cross dir locking */
diff --git a/fs/overlayfs/dir.c b/fs/overlayfs/dir.c
index 4fc221ea6480..cee35d69e0e6 100644
--- a/fs/overlayfs/dir.c
+++ b/fs/overlayfs/dir.c
@@ -43,6 +43,21 @@ int ovl_cleanup(struct ovl_fs *ofs, struct inode *wdir, struct dentry *wdentry)
 	return err;
 }
 
+int ovl_cleanup_unlocked(struct ovl_fs *ofs, struct dentry *workdir,
+			 struct dentry *wdentry)
+{
+	int err;
+
+	err = parent_lock(workdir, wdentry);
+	if (err)
+		return err;
+
+	ovl_cleanup(ofs, workdir->d_inode, wdentry);
+	parent_unlock(workdir);
+
+	return err;
+}
+
 struct dentry *ovl_lookup_temp(struct ovl_fs *ofs, struct dentry *workdir)
 {
 	struct dentry *temp;
diff --git a/fs/overlayfs/overlayfs.h b/fs/overlayfs/overlayfs.h
index 42228d10f6b9..68dc78c712a8 100644
--- a/fs/overlayfs/overlayfs.h
+++ b/fs/overlayfs/overlayfs.h
@@ -416,6 +416,11 @@ static inline bool ovl_open_flags_need_copy_up(int flags)
 }
 
 /* util.c */
+int parent_lock(struct dentry *parent, struct dentry *child);
+static inline void parent_unlock(struct dentry *parent)
+{
+	inode_unlock(parent->d_inode);
+}
 int ovl_get_write_access(struct dentry *dentry);
 void ovl_put_write_access(struct dentry *dentry);
 void ovl_start_write(struct dentry *dentry);
@@ -843,6 +848,7 @@ struct dentry *ovl_create_real(struct ovl_fs *ofs,
 			       struct inode *dir, struct dentry *newdentry,
 			       struct ovl_cattr *attr);
 int ovl_cleanup(struct ovl_fs *ofs, struct inode *dir, struct dentry *dentry);
+int ovl_cleanup_unlocked(struct ovl_fs *ofs, struct dentry *workdir, struct dentry *dentry);
 struct dentry *ovl_lookup_temp(struct ovl_fs *ofs, struct dentry *workdir);
 struct dentry *ovl_create_temp(struct ovl_fs *ofs, struct dentry *workdir,
 			       struct ovl_cattr *attr);
diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 2b4754c645ee..a5105d68f6b4 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -1544,3 +1544,13 @@ void ovl_copyattr(struct inode *inode)
 	i_size_write(inode, i_size_read(realinode));
 	spin_unlock(&inode->i_lock);
 }
+
+int parent_lock(struct dentry *parent, struct dentry *child)
+{
+	inode_lock_nested(parent->d_inode, I_MUTEX_PARENT);
+	if (!child || child->d_parent == parent)
+		return 0;
+
+	inode_unlock(parent->d_inode);
+	return -EINVAL;
+}
-- 
2.49.0