netdev - Re: [PATCH v2 net-next 02/11] af_unix: Define locking order for U_LOCK_SECOND in unix_state_double

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Date: Tue, 11 Jun 2024 19:16:25 -0400
From: Kent Overstreet <kent.overstreet@...ux.dev>
To: Kuniyuki Iwashima <kuniyu@...zon.com>
Cc: "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>, 
	Paolo Abeni <pabeni@...hat.com>, Kuniyuki Iwashima <kuni1840@...il.com>, netdev@...r.kernel.org
Subject: Re: [PATCH v2 net-next 02/11] af_unix: Define locking order for
 U_LOCK_SECOND in unix_state_double_lock().

On Tue, Jun 11, 2024 at 03:28:56PM GMT, Kuniyuki Iwashima wrote:
> unix_dgram_connect() and unix_dgram_{send,recv}msg() lock the socket
> and peer in ascending order of the socket address.
> 
> Let's define the order as unix_state_lock_cmp_fn() instead of using
> unix_state_lock_nested().
> 
> Signed-off-by: Kuniyuki Iwashima <kuniyu@...zon.com>

Reviewed-by: Kent Overstreet <kent.overstreet@...ux.dev>

> ---
>  net/unix/af_unix.c | 16 +++++++++++++++-
>  1 file changed, 15 insertions(+), 1 deletion(-)
> 
> diff --git a/net/unix/af_unix.c b/net/unix/af_unix.c
> index 22bb941f174e..c09bf2b03582 100644
> --- a/net/unix/af_unix.c
> +++ b/net/unix/af_unix.c
> @@ -134,6 +134,18 @@ static int unix_table_lock_cmp_fn(const struct lockdep_map *a,
>  {
>  	return cmp_ptr(a, b);
>  }
> +
> +static int unix_state_lock_cmp_fn(const struct lockdep_map *_a,
> +				  const struct lockdep_map *_b)
> +{
> +	const struct unix_sock *a, *b;
> +
> +	a = container_of(_a, struct unix_sock, lock.dep_map);
> +	b = container_of(_b, struct unix_sock, lock.dep_map);
> +
> +	/* unix_state_double_lock(): ascending address order. */
> +	return cmp_ptr(a, b);
> +}
>  #endif
>  
>  static unsigned int unix_unbound_hash(struct sock *sk)
> @@ -987,6 +999,7 @@ static struct sock *unix_create1(struct net *net, struct socket *sock, int kern,
>  	u->path.dentry = NULL;
>  	u->path.mnt = NULL;
>  	spin_lock_init(&u->lock);
> +	lock_set_cmp_fn(&u->lock, unix_state_lock_cmp_fn, NULL);
>  	mutex_init(&u->iolock); /* single task reading lock */
>  	mutex_init(&u->bindlock); /* single task binding lock */
>  	init_waitqueue_head(&u->peer_wait);
> @@ -1335,11 +1348,12 @@ static void unix_state_double_lock(struct sock *sk1, struct sock *sk2)
>  		unix_state_lock(sk1);
>  		return;
>  	}
> +
>  	if (sk1 > sk2)
>  		swap(sk1, sk2);
>  
>  	unix_state_lock(sk1);
> -	unix_state_lock_nested(sk2, U_LOCK_SECOND);
> +	unix_state_lock(sk2);
>  }
>  
>  static void unix_state_double_unlock(struct sock *sk1, struct sock *sk2)
> -- 
> 2.30.2
>