__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 change 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, hold the rcu_read_lock so we can ensure that any d_parent we find won't go away. Change get_nonsnap_parent to return an inode, and take a reference to that inode before returning (if any). Change 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 <jlayton@xxxxxxxxxx> --- fs/ceph/mds_client.c | 67 +++++++++++++++++++++++++++++++++++----------------- 1 file changed, 45 insertions(+), 22 deletions(-) v2: try to use req->r_locked_dir if d_inode_rcu(parent) is NULL diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c index 815acd1a56d4..eef772155ab1 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_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); - - if (dir->i_sb != mdsc->fsc->sb) { + struct dentry *parent; + struct inode *dir; + + rcu_read_lock(); + parent = req->r_dentry->d_parent; + dir = d_inode_rcu(parent); + + if (!dir) { + inode = req->r_locked_dir; + if (inode) + ihold(inode); + } else if (dir->i_sb != mdsc->fsc->sb) { /* not this fs! */ inode = d_inode(req->r_dentry); + 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: -- 2.7.4 -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
