[PATCH 3/3] NFSD: Annotate caller preconditions for the state-table walkers

The state-table walkers now assert nfsd_mutex with
lockdep_assert_held() and document the nfsd_mutex / nn->nfsd_serv
precondition in a Context: kdoc section, so the next caller added to
this path cannot silently reintroduce the same use-after-free.

Signed-off-by: Chuck Lever <[email protected]>
---
 fs/nfsd/nfs4proc.c  |  6 ++++++
 fs/nfsd/nfs4state.c | 16 +++++++++++++++-
 2 files changed, 21 insertions(+), 1 deletion(-)

diff --git a/fs/nfsd/nfs4proc.c b/fs/nfsd/nfs4proc.c
index eb8a2a16839f..3e4de45aa360 100644
--- a/fs/nfsd/nfs4proc.c
+++ b/fs/nfsd/nfs4proc.c
@@ -1587,6 +1587,11 @@ static bool nfsd4_copy_on_sb(const struct nfsd4_copy *copy,
  * nfsd4_cancel_copy_by_sb - cancel async copy operations on @sb
  * @net: net namespace containing the copy operations
  * @sb: targeted superblock
+ *
+ * Context: Caller must hold nfsd_mutex with nn->nfsd_serv confirmed
+ *          non-NULL.  nfs4_state_destroy_net() frees conf_id_hashtbl
+ *          at server shutdown without clearing the pointer, so a
+ *          walk without these guarantees iterates freed slab memory.
  */
 void nfsd4_cancel_copy_by_sb(struct net *net, struct super_block *sb)
 {
@@ -1596,6 +1601,7 @@ void nfsd4_cancel_copy_by_sb(struct net *net, struct super_block *sb)
 	unsigned int idhashval;
 	LIST_HEAD(to_cancel);
 
+	lockdep_assert_held(&nfsd_mutex);
 	spin_lock(&nn->client_lock);
 	for (idhashval = 0; idhashval < CLIENT_HASH_SIZE; idhashval++) {
 		struct list_head *head = &nn->conf_id_hashtbl[idhashval];
diff --git a/fs/nfsd/nfs4state.c b/fs/nfsd/nfs4state.c
index bef0ec9be459..2a6a0c9ef65f 100644
--- a/fs/nfsd/nfs4state.c
+++ b/fs/nfsd/nfs4state.c
@@ -1873,14 +1873,21 @@ static void revoke_one_stid(struct nfsd_net *nn, struct nfs4_client *clp,
  * being released.  Thus nfsd will no longer prevent the filesystem from being
  * unmounted.
  *
- * The clients which own the states will subsequently being notified that the
+ * The clients which own the states will subsequently be notified that the
  * states have been "admin-revoked".
+ *
+ * Context: Caller must hold nfsd_mutex with nn->nfsd_serv confirmed
+ *          non-NULL.  nfs4_state_destroy_net() frees conf_id_hashtbl
+ *          at server shutdown without clearing the pointer, so a
+ *          walk without these guarantees iterates freed slab memory.
  */
 void nfsd4_revoke_states(struct nfsd_net *nn, struct super_block *sb)
 {
 	unsigned int idhashval;
 	unsigned int sc_types;
 
+	lockdep_assert_held(&nfsd_mutex);
+
 	sc_types = SC_TYPE_OPEN | SC_TYPE_LOCK | SC_TYPE_DELEG | SC_TYPE_LAYOUT;
 
 	spin_lock(&nn->client_lock);
@@ -1946,12 +1953,19 @@ static struct nfs4_stid *find_one_export_stid(struct nfs4_client *clp,
  *
  * Userspace (exportfs -u) sends this after removing the last client
  * for a path, enabling the underlying filesystem to be unmounted.
+ *
+ * Context: Caller must hold nfsd_mutex with nn->nfsd_serv confirmed
+ *          non-NULL.  nfs4_state_destroy_net() frees conf_id_hashtbl
+ *          at server shutdown without clearing the pointer, so a
+ *          walk without these guarantees iterates freed slab memory.
  */
 void nfsd4_revoke_export_states(struct nfsd_net *nn, const struct path *path)
 {
 	unsigned int idhashval;
 	unsigned int sc_types;
 
+	lockdep_assert_held(&nfsd_mutex);
+
 	sc_types = SC_TYPE_OPEN | SC_TYPE_LOCK | SC_TYPE_DELEG | SC_TYPE_LAYOUT;
 
 	spin_lock(&nn->client_lock);

-- 
2.54.0