Bluetooth: fix crash by disabling tasklet in sock accept

Crash can happen when tasklet handling connect/disconnect requests
preempts socket accept. Can be reproduced with "l2test -r" on one
side and several "l2test -c -b 1000 -i hci0 -P 10 <bdaddr>" on the
other side.

disable taskets in socket accept and change lock_sock and release_sock
to bh_lock_sock and bh_unlock_sock since we have to use spinlocks and
there is no need to mark sock as owned by user.

...
[ 3555.897247] Unable to handle kernel NULL pointer dereference at virtual
address 000000bc
[ 3555.915039] pgd = cab9c000
[ 3555.917785] [000000bc] *pgd=8bf3d031, *pte=00000000, *ppte=00000000
[ 3555.928314] Internal error: Oops: 17 [#1] PREEMPT
[ 3555.999786] CPU: 0    Not tainted  (2.6.32.21-13874-g67918ef #65)
...
[ 3556.005981] PC is at bt_accept_unlink+0x20/0x58 [bluetooth]
[ 3556.011627] LR is at bt_accept_dequeue+0x3c/0xe8 [bluetooth]
...
[ 3556.161285] [<bf0007fc>] (bt_accept_unlink+0x20/0x58 [bluetooth]) from
[<bf000870>] (bt_accept_dequeue+0x3c/0xe8 [bluetooth])
[ 3556.172729] [<bf000870>] (bt_accept_dequeue+0x3c/0xe8 [bluetooth]) from
[<bf324df8>] (l2cap_sock_accept+0x100/0x15c [l2cap])
[ 3556.184082] [<bf324df8>] (l2cap_sock_accept+0x100/0x15c [l2cap]) from
[<c026a0a8>] (sys_accept4+0x120/0x1e0)
[ 3556.193969] [<c026a0a8>] (sys_accept4+0x120/0x1e0) from [<c002c9a0>]
(ret_fast_syscall+0x0/0x2c)
[ 3556.202819] Code: e5813000 e5901164 e580c160 e580c15c (e1d13bbc)
...
Signed-off-by: Andrei Emeltchenko <andrei.emeltchenko@nokia.com>
Signed-off-by: Gustavo F. Padovan <padovan@profusion.mobi>

net/bluetooth/af_bluetooth.c

@@ -199,14 +199,15 @@ struct sock *bt_accept_dequeue(struct sock *parent, struct socket *newsock)
 
 	BT_DBG("parent %p", parent);
 
+	local_bh_disable();
 	list_for_each_safe(p, n, &bt_sk(parent)->accept_q) {
 		sk = (struct sock *) list_entry(p, struct bt_sock, accept_q);
 
-		lock_sock(sk);
+		bh_lock_sock(sk);
 
 		/* FIXME: Is this check still needed */
 		if (sk->sk_state == BT_CLOSED) {
-			release_sock(sk);
+			bh_unlock_sock(sk);
 			bt_accept_unlink(sk);
 			continue;
 		}
@@ -216,12 +217,16 @@ struct sock *bt_accept_dequeue(struct sock *parent, struct socket *newsock)
 			bt_accept_unlink(sk);
 			if (newsock)
 				sock_graft(sk, newsock);
-			release_sock(sk);
+
+			bh_unlock_sock(sk);
+			local_bh_enable();
 			return sk;
 		}
 
-		release_sock(sk);
+		bh_unlock_sock(sk);
 	}
+	local_bh_enable();
+
 	return NULL;
 }
 EXPORT_SYMBOL(bt_accept_dequeue);