Lockdep is unhappy if two locks from the same class are held.

Fix the below warning by making __vsock_release() non-recursive -- this
patch is kind of ugly, but it looks to me there is not a better way to
deal with the problem here.

============================================
WARNING: possible recursive locking detected
5.2.0+ #6 Not tainted
--------------------------------------------
a.out/1020 is trying to acquire lock:
0000000074731a98 (sk_lock-AF_VSOCK){+.+.}, at: hvs_release+0x10/0x120 [hv_sock]

but task is already holding lock:
0000000014ff8397 (sk_lock-AF_VSOCK){+.+.}, at: __vsock_release+0x2e/0xf0 [vsock]

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(sk_lock-AF_VSOCK);
  lock(sk_lock-AF_VSOCK);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

2 locks held by a.out/1020:
 #0: 00000000f8bceaa7 (&sb->s_type->i_mutex_key#10){+.+.}, at: __sock_release+0x2d/0xa0
 #1: 0000000014ff8397 (sk_lock-AF_VSOCK){+.+.}, at: __vsock_release+0x2e/0xf0 [vsock]

stack backtrace:
CPU: 7 PID: 1020 Comm: a.out Not tainted 5.2.0+ #6
Call Trace:
 dump_stack+0x67/0x90
 __lock_acquire.cold.66+0x14d/0x1f8
 lock_acquire+0xb5/0x1c0
 lock_sock_nested+0x6d/0x90
 hvs_release+0x10/0x120 [hv_sock]
 __vsock_release+0x24/0xf0 [vsock]
 __vsock_release+0xa0/0xf0 [vsock]
 vsock_release+0x12/0x30 [vsock]
 __sock_release+0x37/0xa0
 sock_close+0x14/0x20
 __fput+0xc1/0x250
 task_work_run+0x98/0xc0
 do_exit+0x3dd/0xc60
 do_group_exit+0x47/0xc0
 get_signal+0x169/0xc60
 do_signal+0x30/0x710
 exit_to_usermode_loop+0x50/0xa0
 do_syscall_64+0x1fc/0x220
 entry_SYSCALL_64_after_hwframe+0x49/0xbe

Signed-off-by: Dexuan Cui <decui@microsoft.com>
---
 net/vmw_vsock/af_vsock.c         | 33 ++++++++++++++++++++++++++++++++-
 net/vmw_vsock/hyperv_transport.c |  2 +-
 2 files changed, 33 insertions(+), 2 deletions(-)

diff --git a/net/vmw_vsock/af_vsock.c b/net/vmw_vsock/af_vsock.c
index ab47bf3..420f605 100644
--- a/net/vmw_vsock/af_vsock.c
+++ b/net/vmw_vsock/af_vsock.c

@@ -638,6 +638,37 @@ struct sock *__vsock_create(struct net *net,
 }
 EXPORT_SYMBOL_GPL(__vsock_create);
 
+static void __vsock_release2(struct sock *sk)
+{
+	if (sk) {
+		struct sk_buff *skb;
+		struct vsock_sock *vsk;
+
+		vsk = vsock_sk(sk);
+
+		/* The release call is supposed to use lock_sock_nested()
+		 * rather than lock_sock(), if a lock should be acquired.
+		 */
+		transport->release(vsk);
+
+		/* Use the nested version to avoid the warning
+		 * "possible recursive locking detected".
+		 */
+		lock_sock_nested(sk, SINGLE_DEPTH_NESTING);

+		sock_orphan(sk);
+		sk->sk_shutdown = SHUTDOWN_MASK;
+
+		while ((skb = skb_dequeue(&sk->sk_receive_queue)))
+			kfree_skb(skb);
+
+		/* This sk can not be a listener, so it's unnecessary
+		 * to call vsock_dequeue_accept().
+		 */
+		release_sock(sk);
+		sock_put(sk);
+	}
+}
+
 static void __vsock_release(struct sock *sk)
 {
 	if (sk) {

@@ -659,7 +690,7 @@ static void __vsock_release(struct sock *sk)
 
 		/* Clean up any sockets that never were accepted. */
 		while ((pending = vsock_dequeue_accept(sk)) != NULL) {
-			__vsock_release(pending);
+			__vsock_release2(pending);
 			sock_put(pending);
 		}
 

diff --git a/net/vmw_vsock/hyperv_transport.c b/net/vmw_vsock/hyperv_transport.c
index 9d864eb..4b126b2 100644
--- a/net/vmw_vsock/hyperv_transport.c
+++ b/net/vmw_vsock/hyperv_transport.c

@@ -559,7 +559,7 @@ static void hvs_release(struct vsock_sock *vsk)
 	struct sock *sk = sk_vsock(vsk);
 	bool remove_sock;
 
-	lock_sock(sk);
+	lock_sock_nested(sk, SINGLE_DEPTH_NESTING);