x25: remove the BKL

This replaces all instances of lock_kernel in x25
with lock_sock, taking care to release the socket
lock around sleeping functions (sock_alloc_send_skb
and skb_recv_datagram). It is not clear whether
this is a correct solution, but it seem to be what
other protocols do in the same situation.

Includes a fix suggested by Eric Dumazet.

Signed-off-by: Arnd Bergmann <[e-mail]>
Acked-by: David S. Miller <[e-mail]>
Tested-by: Andrew Hendry <[e-mail]>
Cc: [e-mail]
Cc: [e-mail]
Cc: Eric Dumazet <[e-mail]>

net/x25/Kconfig

···
 config X25
 	tristate "CCITT X.25 Packet Layer (EXPERIMENTAL)"
 	depends on EXPERIMENTAL
-	depends on BKL # should be fixable
 	---help---
 	  X.25 is a set of standardized network protocols, similar in scope to
 	  frame relay; the one physical line from your box to the X.25 network

net/x25/af_x25.c

···
 #include <linux/errno.h>
 #include <linux/kernel.h>
 #include <linux/sched.h>
-#include <linux/smp_lock.h>
 #include <linux/timer.h>
 #include <linux/string.h>
 #include <linux/net.h>
···
 	sock_put(sk);
 }
 
-static void x25_destroy_socket(struct sock *sk)
-{
-	sock_hold(sk);
-	lock_sock(sk);
-	__x25_destroy_socket(sk);
-	release_sock(sk);
-	sock_put(sk);
-}
-
 /*
  *	Handling for system calls applied via the various interfaces to a
  *	X.25 socket object.
···
 	struct sock *sk = sock->sk;
 	struct x25_sock *x25;
 
-	lock_kernel();
 	if (!sk)
-		goto out;
+		return 0;
 
 	x25 = x25_sk(sk);
 
+	sock_hold(sk);
+	lock_sock(sk);
 	switch (x25->state) {
 
 		case X25_STATE_0:
 		case X25_STATE_2:
 			x25_disconnect(sk, 0, 0, 0);
-			x25_destroy_socket(sk);
+			__x25_destroy_socket(sk);
 			goto out;
 
 		case X25_STATE_1:
···
 
 	sock_orphan(sk);
 out:
-	unlock_kernel();
+	release_sock(sk);
+	sock_put(sk);
 	return 0;
 }
 
···
 	size_t size;
 	int qbit = 0, rc = -EINVAL;
 
-	lock_kernel();
+	lock_sock(sk);
 	if (msg->msg_flags & ~(MSG_DONTWAIT|MSG_OOB|MSG_EOR|MSG_CMSG_COMPAT))
 		goto out;
 
···
 
 	size = len + X25_MAX_L2_LEN + X25_EXT_MIN_LEN;
 
+	release_sock(sk);
 	skb = sock_alloc_send_skb(sk, size, noblock, &rc);
+	lock_sock(sk);
 	if (!skb)
 		goto out;
 	X25_SKB_CB(skb)->flags = msg->msg_flags;
···
 			len++;
 	}
 
-	/*
-	 * lock_sock() is currently only used to serialize this x25_kick()
-	 * against input-driven x25_kick() calls. It currently only blocks
-	 * incoming packets for this socket and does not protect against
-	 * any other socket state changes and is not called from anywhere
-	 * else. As x25_kick() cannot block and as long as all socket
-	 * operations are BKL-wrapped, we don't need take to care about
-	 * purging the backlog queue in x25_release().
-	 *
-	 * Using lock_sock() to protect all socket operations entirely
-	 * (and making the whole x25 stack SMP aware) unfortunately would
-	 * require major changes to {send,recv}msg and skb allocation methods.
-	 * -> 2.5 ;)
-	 */
-	lock_sock(sk);
 	x25_kick(sk);
-	release_sock(sk);
 	rc = len;
 out:
-	unlock_kernel();
+	release_sock(sk);
 	return rc;
 out_kfree_skb:
 	kfree_skb(skb);
···
 	unsigned char *asmptr;
 	int rc = -ENOTCONN;
 
-	lock_kernel();
+	lock_sock(sk);
 	/*
 	 * This works for seqpacket too. The receiver has ordered the queue for
 	 * us! We do one quick check first though
···
 		msg->msg_flags |= MSG_OOB;
 	} else {
 		/* Now we can treat all alike */
+		release_sock(sk);
 		skb = skb_recv_datagram(sk, flags & ~MSG_DONTWAIT,
 					flags & MSG_DONTWAIT, &rc);
+		lock_sock(sk);
 		if (!skb)
 			goto out;
 
···
 
 	msg->msg_namelen = sizeof(struct sockaddr_x25);
 
-	lock_sock(sk);
 	x25_check_rbuf(sk);
-	release_sock(sk);
 	rc = copied;
 out_free_dgram:
 	skb_free_datagram(sk, skb);
 out:
-	unlock_kernel();
+	release_sock(sk);
 	return rc;
 }
 
···
 
 		case SIOCX25CALLACCPTAPPRV: {
 			rc = -EINVAL;
-			lock_kernel();
+			lock_sock(sk);
 			if (sk->sk_state != TCP_CLOSE)
 				break;
 			clear_bit(X25_ACCPT_APPRV_FLAG, &x25->flags);
-			unlock_kernel();
+			release_sock(sk);
 			rc = 0;
 			break;
 		}
 
 		case SIOCX25SENDCALLACCPT:  {
 			rc = -EINVAL;
-			lock_kernel();
+			lock_sock(sk);
 			if (sk->sk_state != TCP_ESTABLISHED)
 				break;
 			/* must call accptapprv above */
···
 				break;
 			x25_write_internal(sk, X25_CALL_ACCEPTED);
 			x25->state = X25_STATE_3;
-			unlock_kernel();
+			release_sock(sk);
 			rc = 0;
 			break;
 		}

net/x25/x25_out.c

···
 		frontlen = skb_headroom(skb);
 
 		while (skb->len > 0) {
-			if ((skbn = sock_alloc_send_skb(sk, frontlen + max_len,
-							noblock, &err)) == NULL){
+			release_sock(sk);
+			skbn = sock_alloc_send_skb(sk, frontlen + max_len,
+						   noblock, &err);
+			lock_sock(sk);
+			if (!skbn) {
 				if (err == -EWOULDBLOCK && noblock){
 					kfree_skb(skb);
 					return sent;