netdev - Re: [PATCH net-next] net: add annotation for sock_{lock,unlock}

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Message-ID: <20201116222750.nmfyxnj6jvd3rww4@ltop.local>
Date:   Mon, 16 Nov 2020 23:27:50 +0100
From:   Luc Van Oostenryck <luc.vanoostenryck@...il.com>
To:     Paolo Abeni <pabeni@...hat.com>
Cc:     netdev@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        linux-sparse@...r.kernel.org
Subject: Re: [PATCH net-next] net: add annotation for sock_{lock,unlock}_fast

On Mon, Nov 16, 2020 at 11:36:39AM +0100, Paolo Abeni wrote:
> The static checker is fooled by the non-static locking scheme
> implemented by the mentioned helpers.
> Let's make its life easier adding some unconditional annotation
> so that the helpers are now interpreted as a plain spinlock from
> sparse.
> 
> Signed-off-by: Paolo Abeni <pabeni@...hat.com>
> ---
>  include/net/sock.h | 9 ++++++---
>  net/core/sock.c    | 3 ++-
>  2 files changed, 8 insertions(+), 4 deletions(-)
> 
> diff --git a/include/net/sock.h b/include/net/sock.h
> index 1d29aeae74fd..60d321c6b5a5 100644
> --- a/include/net/sock.h
> +++ b/include/net/sock.h
> @@ -1595,7 +1595,8 @@ void release_sock(struct sock *sk);
>  				SINGLE_DEPTH_NESTING)
>  #define bh_unlock_sock(__sk)	spin_unlock(&((__sk)->sk_lock.slock))
>  
> -bool lock_sock_fast(struct sock *sk);
> +bool lock_sock_fast(struct sock *sk) __acquires(&sk->sk_lock.slock);
> +

Good.

>  /**
>   * unlock_sock_fast - complement of lock_sock_fast
>   * @sk: socket
> @@ -1606,10 +1607,12 @@ bool lock_sock_fast(struct sock *sk);
>   */
>  static inline void unlock_sock_fast(struct sock *sk, bool slow)
>  {
> -	if (slow)
> +	if (slow) {
>  		release_sock(sk);
> -	else
> +		__release(&sk->sk_lock.slock);

The correct solution would be to annotate the declaration of
release_sock() with '__releases(&sk->sk_lock.slock)'.

>  /* Used by processes to "lock" a socket state, so that
> diff --git a/net/core/sock.c b/net/core/sock.c
> index 727ea1cc633c..9badbe7bb4e4 100644
> --- a/net/core/sock.c
> +++ b/net/core/sock.c
> @@ -3078,7 +3078,7 @@ EXPORT_SYMBOL(release_sock);
>   *
>   *   sk_lock.slock unlocked, owned = 1, BH enabled
>   */
> -bool lock_sock_fast(struct sock *sk)
> +bool lock_sock_fast(struct sock *sk) __acquires(&sk->sk_lock.slock)
>  {
>  	might_sleep();
>  	spin_lock_bh(&sk->sk_lock.slock);
> @@ -3096,6 +3096,7 @@ bool lock_sock_fast(struct sock *sk)
>  	 * The sk_lock has mutex_lock() semantics here:
>  	 */
>  	mutex_acquire(&sk->sk_lock.dep_map, 0, 0, _RET_IP_);
> +	__acquire(&sk->sk_lock.slock);

OK, given that the mutexes are not annotated.

-- Luc