From patchwork Wed Dec 14 14:54:26 2016 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jeff Layton X-Patchwork-Id: 9474303 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 0FB9760824 for ; Wed, 14 Dec 2016 14:54:45 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 00A4A28718 for ; Wed, 14 Dec 2016 14:54:45 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id E990A28730; Wed, 14 Dec 2016 14:54:44 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-6.9 required=2.0 tests=BAYES_00,RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id F3DED28718 for ; Wed, 14 Dec 2016 14:54:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932651AbcLNOyk (ORCPT ); Wed, 14 Dec 2016 09:54:40 -0500 Received: from mx1.redhat.com ([209.132.183.28]:45386 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932599AbcLNOye (ORCPT ); Wed, 14 Dec 2016 09:54:34 -0500 Received: from int-mx11.intmail.prod.int.phx2.redhat.com (int-mx11.intmail.prod.int.phx2.redhat.com [10.5.11.24]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mx1.redhat.com (Postfix) with ESMTPS id 19E221E2A; Wed, 14 Dec 2016 14:54:33 +0000 (UTC) Received: from tleilax.poochiereds.net (ovpn-116-64.rdu2.redhat.com [10.10.116.64]) by int-mx11.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id uBEEsUMu012731; Wed, 14 Dec 2016 09:54:32 -0500 From: Jeff Layton To: ceph-devel@vger.kernel.org Cc: zyan@redhat.com, sage@redhat.com, idryomov@gmail.com, linux-fsdevel@vger.kernel.org, dhowells@redhat.com, viro@ZenIV.linux.org.uk Subject: [PATCH v3 1/5] ceph: clean up unsafe d_parent access in __choose_mds Date: Wed, 14 Dec 2016 09:54:26 -0500 Message-Id: <1481727270-12666-2-git-send-email-jlayton@redhat.com> In-Reply-To: <1481727270-12666-1-git-send-email-jlayton@redhat.com> References: <1481727270-12666-1-git-send-email-jlayton@redhat.com> X-Scanned-By: MIMEDefang 2.68 on 10.5.11.24 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Wed, 14 Dec 2016 14:54:33 +0000 (UTC) Sender: ceph-devel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: ceph-devel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP __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: Jeff Layton --- fs/ceph/mds_client.c | 67 +++++++++++++++++++++++++++++++++++----------------- 1 file changed, 45 insertions(+), 22 deletions(-) diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c index 815acd1a56d4..e62b566d3817 100644 --- a/fs/ceph/mds_client.c +++ b/fs/ceph/mds_client.c @@ -667,6 +667,27 @@ static void __unregister_request(struct ceph_mds_client *mdsc, } /* + * 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. * Otherwise, consult frag tree and/or caps to identify the @@ -674,19 +695,6 @@ 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) { @@ -716,30 +724,42 @@ 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_locked_dir) { + inode = req->r_locked_dir; + 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; + + rcu_read_lock(); + parent = req->r_dentry->d_parent; + dir = d_inode_rcu(parent); - if (dir->i_sb != mdsc->fsc->sb) { - /* not this fs! */ + 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, @@ -768,7 +788,7 @@ 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 @@ -783,7 +803,7 @@ 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; } } } @@ -796,6 +816,7 @@ 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; @@ -803,6 +824,8 @@ 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: