A delayed operation such as hci_sync on a given hci_conn needs to take
hci_conn_get, so that the hci_conn doesn't get freed in the meantime.
This does not guarantee the conn is still alive in a valid state, as it
may be cleaned up in the meantime, so one needs to check if it is still
in conn_hash to know if it's still alive.
Simplify this alive check, using HCI_CONN_DELETED flag. This is also
meaningful with RCU lock only, but with slightly different semantics.
If hci_conn_is_alive(conn) returns true inside rcu_read_lock, conn was
in conn_hash from the point of view of the current task when the flag
was read. Then its deletion cannot complete before rcu_read_unlock.
Signed-off-by: Pauli Virtanen <pav@xxxxxx>
---
Notes:
This probably can be done with RCU primitives setting list.prev, but
that's maybe more magical...
include/net/bluetooth/hci_core.h | 18 ++++++++++++++++++
net/bluetooth/hci_conn.c | 10 +---------
2 files changed, 19 insertions(+), 9 deletions(-)
diff --git a/include/net/bluetooth/hci_core.h b/include/net/bluetooth/hci_core.h
index 05a9b3ab3f56..cab39bdd0592 100644
--- a/include/net/bluetooth/hci_core.h
+++ b/include/net/bluetooth/hci_core.h
@@ -978,6 +978,7 @@ enum {
HCI_CONN_PER_ADV,
HCI_CONN_BIG_CREATED,
HCI_CONN_CREATE_CIS,
+ HCI_CONN_DELETED,
};
static inline bool hci_conn_ssp_enabled(struct hci_conn *conn)
@@ -997,6 +998,7 @@ static inline bool hci_conn_sc_enabled(struct hci_conn *conn)
static inline void hci_conn_hash_add(struct hci_dev *hdev, struct hci_conn *c)
{
struct hci_conn_hash *h = &hdev->conn_hash;
+ WARN_ON(test_bit(HCI_CONN_DELETED, &c->flags));
list_add_tail_rcu(&c->list, &h->list);
switch (c->type) {
case ACL_LINK:
@@ -1023,6 +1025,10 @@ static inline void hci_conn_hash_add(struct hci_dev *hdev, struct hci_conn *c)
static inline void hci_conn_hash_del(struct hci_dev *hdev, struct hci_conn *c)
{
struct hci_conn_hash *h = &hdev->conn_hash;
+ bool deleted;
+
+ deleted = test_and_set_bit(HCI_CONN_DELETED, &c->flags);
+ WARN_ON(deleted);
list_del_rcu(&c->list);
synchronize_rcu();
@@ -1049,6 +1055,18 @@ static inline void hci_conn_hash_del(struct hci_dev *hdev, struct hci_conn *c)
}
}
+/* With hdev->lock: whether hci_conn is in conn_hash.
+ * With RCU: if true, the hci_conn is valid conn_hash iteration cursor and
+ * hci_conn_hash_del has not completed. (Note that if hci_conn was obtained in
+ * this critical section it is always valid, but this may return false!)
+ */
+static inline bool hci_conn_is_alive(struct hci_dev *hdev, struct hci_conn *c)
+{
+ RCU_LOCKDEP_WARN(lockdep_is_held(&hdev->lock) || rcu_read_lock_held(),
+ "suspicious locking");
+ return !test_bit(HCI_CONN_DELETED, &c->flags);
+}
+
static inline unsigned int hci_conn_num(struct hci_dev *hdev, __u8 type)
{
struct hci_conn_hash *h = &hdev->conn_hash;
diff --git a/net/bluetooth/hci_conn.c b/net/bluetooth/hci_conn.c
index 62a7ccfdfe63..d489a4829be7 100644
--- a/net/bluetooth/hci_conn.c
+++ b/net/bluetooth/hci_conn.c
@@ -183,21 +183,13 @@ static void le_scan_cleanup(struct work_struct *work)
struct hci_conn *conn = container_of(work, struct hci_conn,
le_scan_cleanup);
struct hci_dev *hdev = conn->hdev;
- struct hci_conn *c = NULL;
BT_DBG("%s hcon %p", hdev->name, conn);
hci_dev_lock(hdev);
/* Check that the hci_conn is still around */
- rcu_read_lock();
- list_for_each_entry_rcu(c, &hdev->conn_hash.list, list) {
- if (c == conn)
- break;
- }
- rcu_read_unlock();
-
- if (c == conn) {
+ if (hci_conn_is_alive(hdev, conn)) {
hci_connect_le_scan_cleanup(conn, 0x00);
hci_conn_cleanup(conn);
}
--
2.41.0
