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authorDavid Herrmann <dh.herrmann@gmail.com>2013-04-06 22:28:39 +0400
committerGustavo Padovan <gustavo.padovan@collabora.co.uk>2013-04-17 09:45:22 +0400
commit8d12356f33f819ec0d064e233f7ca8e59eaa38ef (patch)
treeb976b1efc17d3f9d207212253d6cb5167c6b755c /include
parentfc225c3f5d1b6aa6f99c5c300af4605e4923ce79 (diff)
downloadlinux-8d12356f33f819ec0d064e233f7ca8e59eaa38ef.tar.xz
Bluetooth: introduce hci_conn ref-counting
We currently do not allow using hci_conn from outside of HCI-core. However, several other users could make great use of it. This includes HIDP, rfcomm and all other sub-protocols that rely on an active connection. Hence, we now introduce hci_conn ref-counting. We currently never call get_device(). put_device() is exclusively used in hci_conn_del_sysfs(). Hence, we currently never have a greater device-refcnt than 1. Therefore, it is safe to move the put_device() call from hci_conn_del_sysfs() to hci_conn_del() (it's the only caller). In fact, this even fixes a "use-after-free" bug as we access hci_conn after calling hci_conn_del_sysfs() in hci_conn_del(). From now on we can add references to hci_conn objects in other layers (like l2cap_sock, HIDP, rfcomm, ...) and grab a reference via hci_conn_get(). This does _not_ guarantee, that the connection is still alive. But, this isn't what we want. We can simply lock the hci_conn device and use "device_is_registered(hci_conn->dev)" to test that. However, this is hardly necessary as outside users should never rely on the HCI connection to be alive, anyway. Instead, they should solely rely on the device-object to be available. But if sub-devices want the hci_conn object as sysfs parent, they need to be notified when the connection drops. This will be introduced in later patches with l2cap_users. Signed-off-by: David Herrmann <dh.herrmann@gmail.com> Acked-by: Marcel Holtmann <marcel@holtmann.org> Signed-off-by: Gustavo Padovan <gustavo.padovan@collabora.co.uk>
Diffstat (limited to 'include')
-rw-r--r--include/net/bluetooth/hci_core.h31
1 files changed, 31 insertions, 0 deletions
diff --git a/include/net/bluetooth/hci_core.h b/include/net/bluetooth/hci_core.h
index 5590cc4412c6..d324b11a0c8f 100644
--- a/include/net/bluetooth/hci_core.h
+++ b/include/net/bluetooth/hci_core.h
@@ -600,6 +600,37 @@ int hci_conn_switch_role(struct hci_conn *conn, __u8 role);
void hci_conn_enter_active_mode(struct hci_conn *conn, __u8 force_active);
+/*
+ * hci_conn_get() and hci_conn_put() are used to control the life-time of an
+ * "hci_conn" object. They do not guarantee that the hci_conn object is running,
+ * working or anything else. They just guarantee that the object is available
+ * and can be dereferenced. So you can use its locks, local variables and any
+ * other constant data.
+ * Before accessing runtime data, you _must_ lock the object and then check that
+ * it is still running. As soon as you release the locks, the connection might
+ * get dropped, though.
+ *
+ * On the other hand, hci_conn_hold() and hci_conn_drop() are used to control
+ * how long the underlying connection is held. So every channel that runs on the
+ * hci_conn object calls this to prevent the connection from disappearing. As
+ * long as you hold a device, you must also guarantee that you have a valid
+ * reference to the device via hci_conn_get() (or the initial reference from
+ * hci_conn_add()).
+ * The hold()/drop() ref-count is known to drop below 0 sometimes, which doesn't
+ * break because nobody cares for that. But this means, we cannot use
+ * _get()/_drop() in it, but require the caller to have a valid ref (FIXME).
+ */
+
+static inline void hci_conn_get(struct hci_conn *conn)
+{
+ get_device(&conn->dev);
+}
+
+static inline void hci_conn_put(struct hci_conn *conn)
+{
+ put_device(&conn->dev);
+}
+
static inline void hci_conn_hold(struct hci_conn *conn)
{
BT_DBG("hcon %p orig refcnt %d", conn, atomic_read(&conn->refcnt));