Re: [PATCH] vsock: Fix a lockdep warning in __vsock_release()

[Stefano Garzarella <sgarzare@redhat.com>]

On Tue, Aug 20, 2019 at 03:14:22AM +0000, Dexuan Cui wrote:
> 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);

What about using lock_sock_nested() in the __vsock_release() without
define this new function?

> +		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);

Should we update also other transports?

Thanks,
Stefano