bluetooth: rfcomm_dev_state_change deadlock fix
There's logic in __rfcomm_dlc_close:
rfcomm_dlc_lock(d);
d->state = BT_CLOSED;
d->state_changed(d, err);
rfcomm_dlc_unlock(d);
In rfcomm_dev_state_change, it's possible that rfcomm_dev_put try to
take the dlc lock, then we will deadlock.
Here fixed it by unlock dlc before rfcomm_dev_get in
rfcomm_dev_state_change.
why not unlock just before rfcomm_dev_put? it's because there's
another problem. rfcomm_dev_get/rfcomm_dev_del will take
rfcomm_dev_lock, but in rfcomm_dev_add the lock order is :
rfcomm_dev_lock --> dlc lock
so I unlock dlc before the taken of rfcomm_dev_lock.
Actually it's a regression caused by commit
1905f6c736cb618e07eca0c96e60e3c024023428 ("bluetooth :
__rfcomm_dlc_close lock fix"), the dlc state_change could be two
callbacks : rfcomm_sk_state_change and rfcomm_dev_state_change. I
missed the rfcomm_sk_state_change that time.
Thanks Arjan van de Ven <arjan@linux.intel.com> for the effort in
commit 4c8411f8c115def968820a4df6658ccfd55d7f1a ("bluetooth: fix
locking bug in the rfcomm socket cleanup handling") but he missed the
rfcomm_dev_state_change lock issue.
Signed-off-by: Dave Young <hidave.darkstar@gmail.com>
Acked-by: Marcel Holtmann <marcel@holtmann.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/bluetooth/rfcomm/tty.c b/net/bluetooth/rfcomm/tty.c
index c3f749a..c919187 100644
--- a/net/bluetooth/rfcomm/tty.c
+++ b/net/bluetooth/rfcomm/tty.c
@@ -566,11 +566,22 @@
if (dlc->state == BT_CLOSED) {
if (!dev->tty) {
if (test_bit(RFCOMM_RELEASE_ONHUP, &dev->flags)) {
- if (rfcomm_dev_get(dev->id) == NULL)
+ /* Drop DLC lock here to avoid deadlock
+ * 1. rfcomm_dev_get will take rfcomm_dev_lock
+ * but in rfcomm_dev_add there's lock order:
+ * rfcomm_dev_lock -> dlc lock
+ * 2. rfcomm_dev_put will deadlock if it's
+ * the last reference
+ */
+ rfcomm_dlc_unlock(dlc);
+ if (rfcomm_dev_get(dev->id) == NULL) {
+ rfcomm_dlc_lock(dlc);
return;
+ }
rfcomm_dev_del(dev);
rfcomm_dev_put(dev);
+ rfcomm_dlc_lock(dlc);
}
} else
tty_hangup(dev->tty);