On Wed, 2016-12-14 at 16:58 +0800, Yan, Zheng wrote: > > > > 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 > > Yes, good catch. d_parent can go negative if all you hold is the rcu_read_lock. I don't think we need to return an error the case that both are NULL though. In that event, we'll just "goto random" (which is what we generally do in this function when we aren't sure which one to use). I'll respin... Thanks, Jeff > > > > > > 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 > > > -- Jeff Layton <jlayton@xxxxxxxxxx> -- 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
