Re: [PATCH mptcp-next v2 1/2] mptcp: give MPTCP sockets a distinct lockdep class

[Matthieu Baerts <matttbe@kernel.org>]

Hi Geliang,

Thank you for the new version.

On 16/10/2026 03:35, Geliang Tang wrote:
> From: Geliang Tang <tanggeliang@kylinos.cn>
> 
> MPTCP sockets and their subflows share the same k-sk_lock-AF_INET
> lockdep class. When both are kernel sockets, lockdep flags every path
> that holds the MPTCP socket lock and then locks a subflow (setsockopt,
> connect, bind, worker send-ack) as "possible recursive locking".
> 
> Extract the lock reclassification logic from PM listener socket creation
> into mptcp_reclassify_socket() helper to reclassify MPTCP socket locks
> to a distinct class (msk_lock-AF_INET for IPv4, msk_lock-AF_INET6 for
> IPv6). Call it from __mptcp_init_sock() to cover both active (connect)
> and passive (accept/clone) socket creation paths.
> 
> Signed-off-by: Geliang Tang <tanggeliang@kylinos.cn>
> ---
>  net/mptcp/pm_kernel.c | 18 ++++++++++++------
>  net/mptcp/protocol.c  |  3 +++
>  net/mptcp/protocol.h  |  2 ++
>  3 files changed, 17 insertions(+), 6 deletions(-)
> 
> diff --git a/net/mptcp/pm_kernel.c b/net/mptcp/pm_kernel.c
> index d3014bf57bf3..5e8792ad38ca 100644
> --- a/net/mptcp/pm_kernel.c
> +++ b/net/mptcp/pm_kernel.c
> @@ -849,10 +849,20 @@ static int mptcp_pm_nl_append_new_local_addr(struct pm_nl_pernet *pernet,
>  static struct lock_class_key mptcp_slock_keys[2];
>  static struct lock_class_key mptcp_keys[2];
>  
> +void mptcp_reclassify_socket(struct sock *sk)
> +{
> +	bool is_ipv6 = sk->sk_family == AF_INET6;
> +
> +	sock_lock_init_class_and_name(sk,
> +				      is_ipv6 ? "mlock-AF_INET6" : "mlock-AF_INET",
> +				      &mptcp_slock_keys[is_ipv6],
> +				      is_ipv6 ? "msk_lock-AF_INET6" : "msk_lock-AF_INET",
> +				      &mptcp_keys[is_ipv6]);
> +}

Good idea to share this code here, but then I think it should be better
in net/mptcp/protocol.c than in the in-kernel PM.

>  static int mptcp_pm_nl_create_listen_socket(struct sock *sk,
>  					    struct mptcp_pm_addr_entry *entry)
>  {
> -	bool is_ipv6 = entry->addr.family == AF_INET6;
>  	int addrlen = sizeof(struct sockaddr_in);
>  	struct sockaddr_storage addr;
>  	struct sock *newsk, *ssk;
> @@ -874,11 +884,7 @@ static int mptcp_pm_nl_create_listen_socket(struct sock *sk,
>  	 * modifiers in several places, re-init the lock class for the msk
>  	 * socket to an mptcp specific one.
>  	 */
> -	sock_lock_init_class_and_name(newsk,
> -				      is_ipv6 ? "mlock-AF_INET6" : "mlock-AF_INET",
> -				      &mptcp_slock_keys[is_ipv6],
> -				      is_ipv6 ? "msk_lock-AF_INET6" : "msk_lock-AF_INET",
> -				      &mptcp_keys[is_ipv6]);
> +	mptcp_reclassify_socket(newsk);
>  
>  	lock_sock(newsk);
>  	ssk = __mptcp_nmpc_sk(mptcp_sk(newsk));
> diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c
> index 60cbd91be632..68f339311993 100644
> --- a/net/mptcp/protocol.c
> +++ b/net/mptcp/protocol.c
> @@ -3245,6 +3245,9 @@ static void __mptcp_init_sock(struct sock *sk)
>  	/* re-use the csk retrans timer for MPTCP-level retrans */
>  	timer_setup(&sk->mptcp_retransmit_timer, mptcp_retransmit_timer, 0);
>  	timer_setup(&msk->sk.mptcp_tout_timer, mptcp_tout_timer, 0);
> +
> +	if (sk->sk_socket)

If you need this check here, that means the reclassification is not
always done, thus this new helper is certainly called from the wrong place.

> +		mptcp_reclassify_socket(sk);
>  }
>  
>  static void mptcp_ca_reset(struct sock *sk)
> diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h
> index ed2f363bb915..325499e65236 100644
> --- a/net/mptcp/protocol.h
> +++ b/net/mptcp/protocol.h
> @@ -1265,6 +1265,8 @@ u8 mptcp_pm_get_endp_fullmesh_max(const struct mptcp_sock *msk);
>  u8 mptcp_pm_get_limit_add_addr_accepted(const struct mptcp_sock *msk);
>  u8 mptcp_pm_get_limit_extra_subflows(const struct mptcp_sock *msk);
>  
> +void mptcp_reclassify_socket(struct sock *sk);
> +
>  /* called under PM lock */
>  static inline void __mptcp_pm_close_subflow(struct mptcp_sock *msk)
>  {

Cheers,
Matt
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