> On 14 Dec 2016, at 02:04, Jeff Layton <jlayton@xxxxxxxxxx> wrote: > > __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 | 59 ++++++++++++++++++++++++++++++++++------------------ > 1 file changed, 39 insertions(+), 20 deletions(-) > > diff --git a/fs/ceph/mds_client.c b/fs/ceph/mds_client.c > index 815acd1a56d4..d51cfd2c6def 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 +724,38 @@ 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; > + > + rcu_read_lock(); > + parent = req->r_dentry->d_parent; > + dir = d_inode_rcu(parent); d_inode_rcu(parent) can return null in theory. I think we should use req->r_locked_dir when it’s not null. If both r_locked_dir and d_inode_rcu(parent) are nulls, return an error return the request sender. Regards Yan, Zheng > > 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 +784,7 @@ 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 +799,7 @@ 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 +812,7 @@ 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 +820,8 @@ 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
