Commit 12487f30 authored by Al Viro's avatar Al Viro
Browse files

follow_dotdot{,_rcu}(): massage loops 



The logics in both of them is the same:
	while true
		if in process' root	// uncommon
			break
		if *not* in mount root	// normal case
			find the parent
			return
		if at absolute root	// very uncommon
			break
		move to underlying mountpoint
	report that we are in root

Pull the common path out of the loop:
	if in process' root		// uncommon
		goto in_root
	if unlikely(in mount root)
		while true
			if at absolute root
				goto in_root
			move to underlying mountpoint
			if in process' root
				goto in_root
			if in mount root
				break;
	find the parent	// we are not in mount root
	return
in_root:
	report that we are in root

The reason for that transformation is that we get to keep the
common path straight *and* get a separate block for "move
through underlying mountpoints", which will allow to sanitize
NO_XDEV handling there.  What's more, the pared-down loops
will be easier to deal with - in particular, non-RCU case
has no need to grab mount_lock and rewriting it to the
form that wouldn't do that is a non-trivial change.  Better
do that with less stuff getting in the way...

Signed-off-by: default avatarAl Viro <viro@zeniv.linux.org.uk>
parent c2df1968

fs/namei.c

+45 −32
Original line number Diff line number Diff line
@@ -1691,21 +1691,12 @@ static struct dentry *follow_dotdot_rcu(struct nameidata *nd, 
					struct inode **inodep,

					unsigned *seqp)

{

	while (1) {

		if (path_equal(&nd->path, &nd->root))

			break;

		if (nd->path.dentry != nd->path.mnt->mnt_root) {

			struct dentry *old = nd->path.dentry;

			struct dentry *parent = old->d_parent;

	struct dentry *parent, *old;



			*inodep = parent->d_inode;

			*seqp = read_seqcount_begin(&parent->d_seq);

			if (unlikely(read_seqcount_retry(&old->d_seq, nd->seq)))

				return ERR_PTR(-ECHILD);

			if (unlikely(!path_connected(nd->path.mnt, parent)))

				return ERR_PTR(-ECHILD);

			return parent;

		} else {

	if (path_equal(&nd->path, &nd->root))

		goto in_root;

	if (unlikely(nd->path.dentry == nd->path.mnt->mnt_root)) {

		while (1) {

			struct mount *mnt = real_mount(nd->path.mnt);

			struct mount *mparent = mnt->mnt_parent;

			struct dentry *mountpoint = mnt->mnt_mountpoint;
@@ -1714,7 +1705,7 @@ static struct dentry *follow_dotdot_rcu(struct nameidata *nd, 
			if (unlikely(read_seqretry(&mount_lock, nd->m_seq)))

				return ERR_PTR(-ECHILD);

			if (&mparent->mnt == nd->path.mnt)

				break;

				goto in_root;

			if (unlikely(nd->flags & LOOKUP_NO_XDEV))

				return ERR_PTR(-ECHILD);

			/* we know that mountpoint was pinned */
@@ -1722,8 +1713,22 @@ static struct dentry *follow_dotdot_rcu(struct nameidata *nd, 
			nd->path.mnt = &mparent->mnt;

			nd->inode = inode;

			nd->seq = seq;

			if (path_equal(&nd->path, &nd->root))

				goto in_root;

			if (nd->path.dentry != nd->path.mnt->mnt_root)

				break;

		}

	}

	old = nd->path.dentry;

	parent = old->d_parent;

	*inodep = parent->d_inode;

	*seqp = read_seqcount_begin(&parent->d_seq);

	if (unlikely(read_seqcount_retry(&old->d_seq, nd->seq)))

		return ERR_PTR(-ECHILD);

	if (unlikely(!path_connected(nd->path.mnt, parent)))

		return ERR_PTR(-ECHILD);

	return parent;

in_root:

	if (unlikely(nd->flags & LOOKUP_BENEATH))

		return ERR_PTR(-ECHILD);

	return NULL;
@@ -1733,12 +1738,24 @@ static struct dentry *follow_dotdot(struct nameidata *nd, 
				 struct inode **inodep,

				 unsigned *seqp)

{

	struct dentry *parent;



	if (path_equal(&nd->path, &nd->root))

		goto in_root;

	if (unlikely(nd->path.dentry == nd->path.mnt->mnt_root)) {

		while (1) {

			if (!follow_up(&nd->path))

				goto in_root;

			if (unlikely(nd->flags & LOOKUP_NO_XDEV))

				return ERR_PTR(-EXDEV);

			if (path_equal(&nd->path, &nd->root))

				goto in_root;

			if (nd->path.dentry != nd->path.mnt->mnt_root)

				break;

		if (nd->path.dentry != nd->path.mnt->mnt_root) {

		}

	}

	/* rare case of legitimate dget_parent()... */

			struct dentry *parent = dget_parent(nd->path.dentry);

	parent = dget_parent(nd->path.dentry);

	if (unlikely(!path_connected(nd->path.mnt, parent))) {

		dput(parent);

		return ERR_PTR(-ENOENT);
@@ -1746,12 +1763,8 @@ static struct dentry *follow_dotdot(struct nameidata *nd, 
	*seqp = 0;

	*inodep = parent->d_inode;

	return parent;

		}

		if (!follow_up(&nd->path))

			break;

		if (unlikely(nd->flags & LOOKUP_NO_XDEV))

			return ERR_PTR(-EXDEV);

	}



in_root:

	if (unlikely(nd->flags & LOOKUP_BENEATH))

		return ERR_PTR(-EXDEV);

	dget(nd->path.dentry);

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