tipc: don't call sock_release() in atomic context

syzbot reported a scheduling while atomic issue at netns
destruction time:

BUG: sleeping function called from invalid context at net/core/sock.c:2769
in_atomic(): 1, irqs_disabled(): 0, pid: 85, name: kworker/u4:3
5 locks held by kworker/u4:3/85:
  #0:  ((wq_completion)"%s""netns"){+.+.}, at: [<00000000c9792deb>]
process_one_work+0xaaf/0x1af0 kernel/workqueue.c:2084
  #1:  (net_cleanup_work){+.+.}, at: [<00000000adc12e2a>]
process_one_work+0xb01/0x1af0 kernel/workqueue.c:2088
  #2:  (net_sem){++++}, at: [<000000009ccb5669>] cleanup_net+0x23f/0xd20
net/core/net_namespace.c:494
  #3:  (net_mutex){+.+.}, at: [<00000000a92767d9>] cleanup_net+0xa7d/0xd20
net/core/net_namespace.c:496
  #4:  (&(&srv->idr_lock)->rlock){+...}, at: [<000000001343e568>]
spin_lock_bh include/linux/spinlock.h:315 [inline]
  #4:  (&(&srv->idr_lock)->rlock){+...}, at: [<000000001343e568>]
tipc_topsrv_stop+0x231/0x610 net/tipc/topsrv.c:685
CPU: 0 PID: 85 Comm: kworker/u4:3 Not tainted 4.16.0-rc1+ #230
Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS
Google 01/01/2011
Workqueue: netns cleanup_net
Call Trace:
  __dump_stack lib/dump_stack.c:17 [inline]
  dump_stack+0x194/0x257 lib/dump_stack.c:53
  ___might_sleep+0x2b2/0x470 kernel/sched/core.c:6128
  __might_sleep+0x95/0x190 kernel/sched/core.c:6081
  lock_sock_nested+0x37/0x110 net/core/sock.c:2769
  lock_sock include/net/sock.h:1463 [inline]
  tipc_release+0x103/0xff0 net/tipc/socket.c:572
  sock_release+0x8d/0x1e0 net/socket.c:594
  tipc_topsrv_stop+0x3c0/0x610 net/tipc/topsrv.c:696
  tipc_exit_net+0x15/0x40 net/tipc/core.c:96
  ops_exit_list.isra.6+0xae/0x150 net/core/net_namespace.c:148
  cleanup_net+0x6ba/0xd20 net/core/net_namespace.c:529
  process_one_work+0xbbf/0x1af0 kernel/workqueue.c:2113
  worker_thread+0x223/0x1990 kernel/workqueue.c:2247
  kthread+0x33c/0x400 kernel/kthread.c:238
  ret_from_fork+0x3a/0x50 arch/x86/entry/entry_64.S:429

This is caused by tipc_topsrv_stop() releasing the listener socket
with the idr lock held. This changeset addresses the issue moving
the release operation outside such lock.

Reported-and-tested-by: syzbot+749d9d87c294c00ca856@syzkaller.appspotmail.com
Fixes: 0ef897be12 ("tipc: separate topology server listener socket from subcsriber sockets")
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Acked-by:  ///jon
Signed-off-by: David S. Miller <davem@davemloft.net>

net/tipc/topsrv.c

@@ -694,9 +694,9 @@ void tipc_topsrv_stop(struct net *net)
 	}
 	__module_get(lsock->ops->owner);
 	__module_get(lsock->sk->sk_prot_creator->owner);
-	sock_release(lsock);
 	srv->listener = NULL;
 	spin_unlock_bh(&srv->idr_lock);
+	sock_release(lsock);
 	tipc_topsrv_work_stop(srv);
 	idr_destroy(&srv->conn_idr);
 	kfree(srv);