[PATCH v2 5/7] nfsd: Fix race in lock stateid creation

[Trond Myklebust <trond.myklebust@primarydata.com>]

If we're looking up a new lock state, and the creation fails, then
we want to unhash it, just like we do for OPEN. However in order
to do so, we need to that no other LOCK requests can grab the
mutex until we have unhashed it (and marked it as closed).

Signed-off-by: Trond Myklebust <trond.myklebust@primarydata.com>
---
 fs/nfsd/nfs4state.c | 104 +++++++++++++++++++++++++++++-----------------------
 1 file changed, 59 insertions(+), 45 deletions(-)

diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index f93ca0682aaa..f13fba4f51ec 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -5630,14 +5630,41 @@ alloc_init_lock_stateowner(unsigned int strhashval, struct nfs4_client *clp,
 	return ret;
 }
 
-static void
+static struct nfs4_ol_stateid *
+find_lock_stateid(struct nfs4_lockowner *lo, struct nfs4_file *fp)
+{
+	struct nfs4_ol_stateid *lst;
+	struct nfs4_client *clp = lo->lo_owner.so_client;
+
+	lockdep_assert_held(&clp->cl_lock);
+
+	list_for_each_entry(lst, &lo->lo_owner.so_stateids, st_perstateowner) {
+		if (lst->st_stid.sc_type != NFS4_LOCK_STID)
+			continue;
+		if (lst->st_stid.sc_file == fp) {
+			atomic_inc(&lst->st_stid.sc_count);
+			return lst;
+		}
+	}
+	return NULL;
+}
+
+static struct nfs4_ol_stateid *
 init_lock_stateid(struct nfs4_ol_stateid *stp, struct nfs4_lockowner *lo,
 		  struct nfs4_file *fp, struct inode *inode,
 		  struct nfs4_ol_stateid *open_stp)
 {
 	struct nfs4_client *clp = lo->lo_owner.so_client;
+	struct nfs4_ol_stateid *retstp;
 
-	lockdep_assert_held(&clp->cl_lock);
+	mutex_init(&stp->st_mutex);
+	mutex_lock(&stp->st_mutex);
+retry:
+	spin_lock(&clp->cl_lock);
+	spin_lock(&fp->fi_lock);
+	retstp = find_lock_stateid(lo, fp);
+	if (retstp)
+		goto out_unlock;
 
 	atomic_inc(&stp->st_stid.sc_count);
 	stp->st_stid.sc_type = NFS4_LOCK_STID;
@@ -5647,31 +5674,22 @@ init_lock_stateid(struct nfs4_ol_stateid *stp, struct nfs4_lockowner *lo,
 	stp->st_access_bmap = 0;
 	stp->st_deny_bmap = open_stp->st_deny_bmap;
 	stp->st_openstp = open_stp;
-	mutex_init(&stp->st_mutex);
 	list_add(&stp->st_locks, &open_stp->st_locks);
 	list_add(&stp->st_perstateowner, &lo->lo_owner.so_stateids);
-	spin_lock(&fp->fi_lock);
 	list_add(&stp->st_perfile, &fp->fi_stateids);
+out_unlock:
 	spin_unlock(&fp->fi_lock);
-}
-
-static struct nfs4_ol_stateid *
-find_lock_stateid(struct nfs4_lockowner *lo, struct nfs4_file *fp)
-{
-	struct nfs4_ol_stateid *lst;
-	struct nfs4_client *clp = lo->lo_owner.so_client;
-
-	lockdep_assert_held(&clp->cl_lock);
-
-	list_for_each_entry(lst, &lo->lo_owner.so_stateids, st_perstateowner) {
-		if (lst->st_stid.sc_type != NFS4_LOCK_STID)
-			continue;
-		if (lst->st_stid.sc_file == fp) {
-			atomic_inc(&lst->st_stid.sc_count);
-			return lst;
+	spin_unlock(&clp->cl_lock);
+	if (retstp) {
+		if (nfsd4_lock_ol_stateid(retstp) != nfs_ok) {
+			nfs4_put_stid(&retstp->st_stid);
+			goto retry;
 		}
+		/* To keep mutex tracking happy */
+		mutex_unlock(&stp->st_mutex);
+		stp = retstp;
 	}
-	return NULL;
+	return stp;
 }
 
 static struct nfs4_ol_stateid *
@@ -5684,26 +5702,25 @@ find_or_create_lock_stateid(struct nfs4_lockowner *lo, struct nfs4_file *fi,
 	struct nfs4_openowner *oo = openowner(ost->st_stateowner);
 	struct nfs4_client *clp = oo->oo_owner.so_client;
 
+	*new = false;
 	spin_lock(&clp->cl_lock);
 	lst = find_lock_stateid(lo, fi);
-	if (lst == NULL) {
-		spin_unlock(&clp->cl_lock);
-		ns = nfs4_alloc_stid(clp, stateid_slab, nfs4_free_lock_stateid);
-		if (ns == NULL)
-			return NULL;
-
-		spin_lock(&clp->cl_lock);
-		lst = find_lock_stateid(lo, fi);
-		if (likely(!lst)) {
-			lst = openlockstateid(ns);
-			init_lock_stateid(lst, lo, fi, inode, ost);
-			ns = NULL;
-			*new = true;
-		}
-	}
 	spin_unlock(&clp->cl_lock);
-	if (ns)
+	if (lst != NULL) {
+		if (nfsd4_lock_ol_stateid(lst) == nfs_ok)
+			goto out;
+		nfs4_put_stid(&lst->st_stid);
+	}
+	ns = nfs4_alloc_stid(clp, stateid_slab, nfs4_free_lock_stateid);
+	if (ns == NULL)
+		return NULL;
+
+	lst = init_lock_stateid(openlockstateid(ns), lo, fi, inode, ost);
+	if (lst == openlockstateid(ns))
+		*new = true;
+	else
 		nfs4_put_stid(ns);
+out:
 	return lst;
 }
 
@@ -5755,17 +5772,12 @@ lookup_or_create_lock_state(struct nfsd4_compound_state *cstate,
 			goto out;
 	}
 
-retry:
 	lst = find_or_create_lock_stateid(lo, fi, inode, ost, new);
 	if (lst == NULL) {
 		status = nfserr_jukebox;
 		goto out;
 	}
 
-	if (nfsd4_lock_ol_stateid(lst) != nfs_ok) {
-		nfs4_put_stid(&lst->st_stid);
-		goto retry;
-	}
 	status = nfs_ok;
 	*plst = lst;
 out:
@@ -5971,14 +5983,16 @@ nfsd4_lock(struct svc_rqst *rqstp, struct nfsd4_compound_state *cstate,
 		    seqid_mutating_err(ntohl(status)))
 			lock_sop->lo_owner.so_seqid++;
 
-		mutex_unlock(&lock_stp->st_mutex);
-
 		/*
 		 * If this is a new, never-before-used stateid, and we are
 		 * returning an error, then just go ahead and release it.
 		 */
-		if (status && new)
+		if (status && new) {
+			lock_stp->st_stid.sc_type = NFS4_CLOSED_STID;
 			release_lock_stateid(lock_stp);
+		}
+
+		mutex_unlock(&lock_stp->st_mutex);
 
 		nfs4_put_stid(&lock_stp->st_stid);
 	}
-- 
2.13.6