[PATCH] scsi: target: tcm_fc: annotate session hash traversals

[Runyu Xiao]

The TCM FC session hash is updated with RCU hlist primitives. Several
writer-side helpers traverse the hash with hlist_for_each_entry_rcu()
while the file-level comments state that the caller holds ft_lport_lock:

ft_sess_create()
ft_sess_delete()
ft_sess_delete_all()

Other tcm_fc paths already use lockdep_is_held(&ft_lport_lock) when
dereferencing RCU-protected local-port state. Pass the same lockdep
condition to these session hash iterators so CONFIG_PROVE_RCU_LIST can
distinguish the ft_lport_lock-protected writer paths from ordinary RCU
readers.

This was found by our static analysis tool and then manually reviewed
against the current tree. In the reviewed CONFIG_PROVE_RCU_LIST triage
runs, the session hash walkers produced the expected "RCU-list traversed
in non-reader section!!" warning with stacks matching ft_sess_create()/
ft_prli_locked(), ft_sess_delete()/ft_prlo(), and ft_sess_delete_all()/
ft_lport_del(). The change is limited to documenting the existing
protection contract.

This is a lockdep annotation cleanup and does not change the session
hash lifetime model.

Signed-off-by: Runyu Xiao <runyu.xiao@xxxxxxxxxx>
---
 drivers/target/tcm_fc/tfc_sess.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

diff --git a/drivers/target/tcm_fc/tfc_sess.c b/drivers/target/tcm_fc/tfc_sess.c
index 797be06ab71b..84a6f29a1b5f 100644
--- a/drivers/target/tcm_fc/tfc_sess.c
+++ b/drivers/target/tcm_fc/tfc_sess.c
@@ -215,7 +215,8 @@ static struct ft_sess *ft_sess_create(struct ft_tport *tport, u32 port_id,
 	ft_format_wwn(&initiatorname[0], TRANSPORT_IQN_LEN, rdata->ids.port_name);
 
 	head = &tport->hash[ft_sess_hash(port_id)];
-	hlist_for_each_entry_rcu(sess, head, hash)
+	hlist_for_each_entry_rcu(sess, head, hash,
+				 lockdep_is_held(&ft_lport_lock))
 		if (sess->port_id == port_id)
 			return sess;
 
@@ -264,7 +265,8 @@ static struct ft_sess *ft_sess_delete(struct ft_tport *tport, u32 port_id)
 	struct ft_sess *sess;
 
 	head = &tport->hash[ft_sess_hash(port_id)];
-	hlist_for_each_entry_rcu(sess, head, hash) {
+	hlist_for_each_entry_rcu(sess, head, hash,
+				 lockdep_is_held(&ft_lport_lock)) {
 		if (sess->port_id == port_id) {
 			ft_sess_unhash(sess);
 			return sess;
@@ -291,7 +293,8 @@ static void ft_sess_delete_all(struct ft_tport *tport)
 
 	for (head = tport->hash;
 	     head < &tport->hash[FT_SESS_HASH_SIZE]; head++) {
-		hlist_for_each_entry_rcu(sess, head, hash) {
+		hlist_for_each_entry_rcu(sess, head, hash,
+					 lockdep_is_held(&ft_lport_lock)) {
 			ft_sess_unhash(sess);
 			ft_close_sess(sess);	/* release from table */
 		}
-- 
2.34.1