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Commit 30c71233 authored by Jeff Layton's avatar Jeff Layton Committed by Ilya Dryomov
Browse files

ceph: clean up unsafe d_parent access in __choose_mds 

__choose_mds exists to pick an MDS to use when issuing a call. Doing
that typically involves picking an inode and using the authoritative
MDS for it. In most cases, that's pretty straightforward, as we are
using an inode to which we hold a reference (usually represented by
r_dentry or r_inode in the request).

In the case of a snapshotted directory however, we need to fetch
the non-snapped parent, which involves walking back up the parents
in the tree. The dentries in the snapshot dir are effectively frozen
but the overall parent is _not_, and could vanish if a concurrent
rename were to occur.

Clean this code up and take special care to ensure the validity of
the entries we're working with. First, try to use the inode in
r_locked_dir if one exists. If not and all we have is r_dentry,
then we have to walk back up the tree. Use the rcu_read_lock for
this so we can ensure that any d_parent we find won't go away, and
take extra care to deal with the possibility that the dentries could
go negative.

Change get_nonsnap_parent to return an inode, and take a reference to
that inode before returning (if any). Change all of the other places
where we set "inode" in __choose_mds to also take a reference, and then
call iput on that inode before exiting the function.

Link: http://tracker.ceph.com/issues/18148


Signed-off-by: default avatarJeff Layton <jlayton@redhat.com>
Reviewed-by: default avatarYan, Zheng <zyan@redhat.com>
Signed-off-by: default avatarIlya Dryomov <idryomov@gmail.com>
parent c470abd4

fs/ceph/mds_client.c

+42 −22
Original line number Diff line number Diff line
@@ -667,6 +667,27 @@ static void __unregister_request(struct ceph_mds_client *mdsc, 
	ceph_mdsc_put_request(req);

}



/*

 * Walk back up the dentry tree until we hit a dentry representing a

 * non-snapshot inode. We do this using the rcu_read_lock (which must be held

 * when calling this) to ensure that the objects won't disappear while we're

 * working with them. Once we hit a candidate dentry, we attempt to take a

 * reference to it, and return that as the result.

 */

static struct inode *get_nonsnap_parent(struct dentry *dentry) { struct inode

	*inode = NULL;



	while (dentry && !IS_ROOT(dentry)) {

		inode = d_inode_rcu(dentry);

		if (!inode || ceph_snap(inode) == CEPH_NOSNAP)

			break;

		dentry = dentry->d_parent;

	}

	if (inode)

		inode = igrab(inode);

	return inode;

}



/*

 * Choose mds to send request to next.  If there is a hint set in the

 * request (e.g., due to a prior forward hint from the mds), use that.
@@ -675,19 +696,6 @@ static void __unregister_request(struct ceph_mds_client *mdsc, 
 *

 * Called under mdsc->mutex.

 */

static struct dentry *get_nonsnap_parent(struct dentry *dentry)

{

	/*

	 * we don't need to worry about protecting the d_parent access

	 * here because we never renaming inside the snapped namespace

	 * except to resplice to another snapdir, and either the old or new

	 * result is a valid result.

	 */

	while (!IS_ROOT(dentry) && ceph_snap(d_inode(dentry)) != CEPH_NOSNAP)

		dentry = dentry->d_parent;

	return dentry;

}



static int __choose_mds(struct ceph_mds_client *mdsc,

			struct ceph_mds_request *req)

{
@@ -717,30 +725,39 @@ static int __choose_mds(struct ceph_mds_client *mdsc, 
	inode = NULL;

	if (req->r_inode) {

		inode = req->r_inode;

		ihold(inode);

	} else if (req->r_dentry) {

		/* ignore race with rename; old or new d_parent is okay */

		struct dentry *parent = req->r_dentry->d_parent;

		struct inode *dir = d_inode(parent);

		struct dentry *parent;

		struct inode *dir;



		if (dir->i_sb != mdsc->fsc->sb) {

			/* not this fs! */

		rcu_read_lock();

		parent = req->r_dentry->d_parent;

		dir = req->r_locked_dir ? : d_inode_rcu(parent);



		if (!dir || dir->i_sb != mdsc->fsc->sb) {

			/*  not this fs or parent went negative */

			inode = d_inode(req->r_dentry);

			if (inode)

				ihold(inode);

		} else if (ceph_snap(dir) != CEPH_NOSNAP) {

			/* direct snapped/virtual snapdir requests

			 * based on parent dir inode */

			struct dentry *dn = get_nonsnap_parent(parent);

			inode = d_inode(dn);

			inode = get_nonsnap_parent(parent);

			dout("__choose_mds using nonsnap parent %p\n", inode);

		} else {

			/* dentry target */

			inode = d_inode(req->r_dentry);

			if (!inode || mode == USE_AUTH_MDS) {

				/* dir + name */

				inode = dir;

				inode = igrab(dir);

				hash = ceph_dentry_hash(dir, req->r_dentry);

				is_hash = true;

			} else {

				ihold(inode);

			}

		}

		rcu_read_unlock();

	}



	dout("__choose_mds %p is_hash=%d (%d) mode %d\n", inode, (int)is_hash,
@@ -769,7 +786,7 @@ static int __choose_mds(struct ceph_mds_client *mdsc, 
				     (int)r, frag.ndist);

				if (ceph_mdsmap_get_state(mdsc->mdsmap, mds) >=

				    CEPH_MDS_STATE_ACTIVE)

					return mds;

					goto out;

			}



			/* since this file/dir wasn't known to be
@@ -784,7 +801,7 @@ static int __choose_mds(struct ceph_mds_client *mdsc, 
				     inode, ceph_vinop(inode), frag.frag, mds);

				if (ceph_mdsmap_get_state(mdsc->mdsmap, mds) >=

				    CEPH_MDS_STATE_ACTIVE)

					return mds;

					goto out;

			}

		}

	}
@@ -797,6 +814,7 @@ static int __choose_mds(struct ceph_mds_client *mdsc, 
		cap = rb_entry(rb_first(&ci->i_caps), struct ceph_cap, ci_node);

	if (!cap) {

		spin_unlock(&ci->i_ceph_lock);

		iput(inode);

		goto random;

	}

	mds = cap->session->s_mds;
@@ -804,6 +822,8 @@ static int __choose_mds(struct ceph_mds_client *mdsc, 
	     inode, ceph_vinop(inode), mds,

	     cap == ci->i_auth_cap ? "auth " : "", cap);

	spin_unlock(&ci->i_ceph_lock);

out:

	iput(inode);

	return mds;



random: