This is a note to let you know that I've just added the patch titled mptcp: fix lockdep false positive to the 6.1-stable tree which can be found at: http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary The filename of the patch is: mptcp-fix-lockdep-false-positive.patch and it can be found in the queue-6.1 subdirectory. If you, or anyone else, feels it should not be added to the stable tree, please let <stable@xxxxxxxxxxxxxxx> know about it. commit 635d909ddd53062e5800684c5a379feb32897e8e Author: Paolo Abeni <pabeni@xxxxxxxxxx> Date: Tue Dec 20 11:52:15 2022 -0800 mptcp: fix lockdep false positive [ Upstream commit fec3adfd754ccc99a7230e8ab9f105b65fb07bcc ] MattB reported a lockdep splat in the mptcp listener code cleanup: WARNING: possible circular locking dependency detected packetdrill/14278 is trying to acquire lock: ffff888017d868f0 ((work_completion)(&msk->work)){+.+.}-{0:0}, at: __flush_work (kernel/workqueue.c:3069) but task is already holding lock: ffff888017d84130 (sk_lock-AF_INET){+.+.}-{0:0}, at: mptcp_close (net/mptcp/protocol.c:2973) which lock already depends on the new lock. the existing dependency chain (in reverse order) is: -> #1 (sk_lock-AF_INET){+.+.}-{0:0}: __lock_acquire (kernel/locking/lockdep.c:5055) lock_acquire (kernel/locking/lockdep.c:466) lock_sock_nested (net/core/sock.c:3463) mptcp_worker (net/mptcp/protocol.c:2614) process_one_work (kernel/workqueue.c:2294) worker_thread (include/linux/list.h:292) kthread (kernel/kthread.c:376) ret_from_fork (arch/x86/entry/entry_64.S:312) -> #0 ((work_completion)(&msk->work)){+.+.}-{0:0}: check_prev_add (kernel/locking/lockdep.c:3098) validate_chain (kernel/locking/lockdep.c:3217) __lock_acquire (kernel/locking/lockdep.c:5055) lock_acquire (kernel/locking/lockdep.c:466) __flush_work (kernel/workqueue.c:3070) __cancel_work_timer (kernel/workqueue.c:3160) mptcp_cancel_work (net/mptcp/protocol.c:2758) mptcp_subflow_queue_clean (net/mptcp/subflow.c:1817) __mptcp_close_ssk (net/mptcp/protocol.c:2363) mptcp_destroy_common (net/mptcp/protocol.c:3170) mptcp_destroy (include/net/sock.h:1495) __mptcp_destroy_sock (net/mptcp/protocol.c:2886) __mptcp_close (net/mptcp/protocol.c:2959) mptcp_close (net/mptcp/protocol.c:2974) inet_release (net/ipv4/af_inet.c:432) __sock_release (net/socket.c:651) sock_close (net/socket.c:1367) __fput (fs/file_table.c:320) task_work_run (kernel/task_work.c:181 (discriminator 1)) exit_to_user_mode_prepare (include/linux/resume_user_mode.h:49) syscall_exit_to_user_mode (kernel/entry/common.c:130) do_syscall_64 (arch/x86/entry/common.c:87) entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:120) other info that might help us debug this: Possible unsafe locking scenario: CPU0 CPU1 ---- ---- lock(sk_lock-AF_INET); lock((work_completion)(&msk->work)); lock(sk_lock-AF_INET); lock((work_completion)(&msk->work)); *** DEADLOCK *** The report is actually a false positive, since the only existing lock nesting is the msk socket lock acquired by the mptcp work. cancel_work_sync() is invoked without the relevant socket lock being held, but under a different (the msk listener) socket lock. We could silence the splat adding a per workqueue dynamic lockdep key, but that looks overkill. Instead just tell lockdep the msk socket lock is not held around cancel_work_sync(). Closes: https://github.com/multipath-tcp/mptcp_net-next/issues/322 Fixes: 30e51b923e43 ("mptcp: fix unreleased socket in accept queue") Reported-by: Matthieu Baerts <matthieu.baerts@xxxxxxxxxxxx> Reviewed-by: Mat Martineau <mathew.j.martineau@xxxxxxxxxxxxxxx> Signed-off-by: Paolo Abeni <pabeni@xxxxxxxxxx> Signed-off-by: Mat Martineau <mathew.j.martineau@xxxxxxxxxxxxxxx> Signed-off-by: Jakub Kicinski <kuba@xxxxxxxxxx> Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx> diff --git a/net/mptcp/protocol.c b/net/mptcp/protocol.c index e64ea2ca1c7a..e97465f0c667 100644 --- a/net/mptcp/protocol.c +++ b/net/mptcp/protocol.c @@ -2371,7 +2371,7 @@ static void __mptcp_close_ssk(struct sock *sk, struct sock *ssk, /* otherwise tcp will dispose of the ssk and subflow ctx */ if (ssk->sk_state == TCP_LISTEN) { tcp_set_state(ssk, TCP_CLOSE); - mptcp_subflow_queue_clean(ssk); + mptcp_subflow_queue_clean(sk, ssk); inet_csk_listen_stop(ssk); } __tcp_close(ssk, 0); diff --git a/net/mptcp/protocol.h b/net/mptcp/protocol.h index 380bddbc52d4..62e9ff237b6e 100644 --- a/net/mptcp/protocol.h +++ b/net/mptcp/protocol.h @@ -614,7 +614,7 @@ void mptcp_close_ssk(struct sock *sk, struct sock *ssk, struct mptcp_subflow_context *subflow); void __mptcp_subflow_send_ack(struct sock *ssk); void mptcp_subflow_reset(struct sock *ssk); -void mptcp_subflow_queue_clean(struct sock *ssk); +void mptcp_subflow_queue_clean(struct sock *sk, struct sock *ssk); void mptcp_sock_graft(struct sock *sk, struct socket *parent); struct socket *__mptcp_nmpc_socket(const struct mptcp_sock *msk); bool __mptcp_close(struct sock *sk, long timeout); diff --git a/net/mptcp/subflow.c b/net/mptcp/subflow.c index 613f515fedf0..9d3701fdb293 100644 --- a/net/mptcp/subflow.c +++ b/net/mptcp/subflow.c @@ -1733,7 +1733,7 @@ static void subflow_state_change(struct sock *sk) } } -void mptcp_subflow_queue_clean(struct sock *listener_ssk) +void mptcp_subflow_queue_clean(struct sock *listener_sk, struct sock *listener_ssk) { struct request_sock_queue *queue = &inet_csk(listener_ssk)->icsk_accept_queue; struct mptcp_sock *msk, *next, *head = NULL; @@ -1782,8 +1782,23 @@ void mptcp_subflow_queue_clean(struct sock *listener_ssk) do_cancel_work = __mptcp_close(sk, 0); release_sock(sk); - if (do_cancel_work) + if (do_cancel_work) { + /* lockdep will report a false positive ABBA deadlock + * between cancel_work_sync and the listener socket. + * The involved locks belong to different sockets WRT + * the existing AB chain. + * Using a per socket key is problematic as key + * deregistration requires process context and must be + * performed at socket disposal time, in atomic + * context. + * Just tell lockdep to consider the listener socket + * released here. + */ + mutex_release(&listener_sk->sk_lock.dep_map, _RET_IP_); mptcp_cancel_work(sk); + mutex_acquire(&listener_sk->sk_lock.dep_map, + SINGLE_DEPTH_NESTING, 0, _RET_IP_); + } sock_put(sk); }