ovl: reorder ovl_want_write() after ovl_inode_lock()

Make the locking order of ovl_inode_lock() strictly between the two
vfs stacked layers, i.e.:
- ovl vfs locks: sb_writers, inode_lock, ...
- ovl_inode_lock
- upper vfs locks: sb_writers, inode_lock, ...

To that effect, move ovl_want_write() into the helpers ovl_nlink_start()
and ovl_copy_up_start which currently take the ovl_inode_lock() after
ovl_want_write().

Signed-off-by: Amir Goldstein <amir73il@gmail.com>

1 files changed, 27 insertions, 7 deletions

diff --git a/fs/overlayfs/util.c b/fs/overlayfs/util.c
index 80f20ca85344..af11c83b7a25 100644
--- a/fs/overlayfs/util.c
+++ b/fs/overlayfs/util.c
@@ -676,16 +676,26 @@ int ovl_copy_up_start(struct dentry *dentry, int flags)
 	int err;
 
 	err = ovl_inode_lock_interruptible(inode);
-	if (!err && ovl_already_copied_up_locked(dentry, flags)) {
+	if (err)
+		return err;
+
+	if (ovl_already_copied_up_locked(dentry, flags))
 		err = 1; /* Already copied up */
-		ovl_inode_unlock(inode);
-	}
+	else
+		err = ovl_want_write(dentry);
+	if (err)
+		goto out_unlock;
+
+	return 0;
 
+out_unlock:
+	ovl_inode_unlock(inode);
 	return err;
 }
 
 void ovl_copy_up_end(struct dentry *dentry)
 {
+	ovl_drop_write(dentry);
 	ovl_inode_unlock(d_inode(dentry));
 }
 
@@ -1088,8 +1098,12 @@ int ovl_nlink_start(struct dentry *dentry)
 	if (err)
 		return err;
 
+	err = ovl_want_write(dentry);
+	if (err)
+		goto out_unlock;
+
 	if (d_is_dir(dentry) || !ovl_test_flag(OVL_INDEX, inode))
-		goto out;
+		return 0;
 
 	old_cred = ovl_override_creds(dentry->d_sb);
 	/*
@@ -1100,10 +1114,15 @@ int ovl_nlink_start(struct dentry *dentry)
 	 */
 	err = ovl_set_nlink_upper(dentry);
 	revert_creds(old_cred);
-
-out:
 	if (err)
-		ovl_inode_unlock(inode);
+		goto out_drop_write;
+
+	return 0;
+
+out_drop_write:
+	ovl_drop_write(dentry);
+out_unlock:
+	ovl_inode_unlock(inode);
 
 	return err;
 }
@@ -1120,6 +1139,7 @@ void ovl_nlink_end(struct dentry *dentry)
 		revert_creds(old_cred);
 	}
 
+	ovl_drop_write(dentry);
 	ovl_inode_unlock(inode);
 }