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mptcp: fix lockdep false positive 

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: 30e51b923e ("mptcp: fix unreleased socket in accept queue")
Reported-by: Matthieu Baerts <matthieu.baerts@tessares.net>
Reviewed-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Mat Martineau <mathew.j.martineau@linux.intel.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
This commit is contained in:
Paolo Abeni 2022-12-20 11:52:15 -08:00 committed by Jakub Kicinski
parent 7d803344fd
commit fec3adfd75
3 changed files with 19 additions and 4 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

2
net/mptcp/protocol.c
View File

@ -2357,7 +2357,7 @@ 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);
mptcp_event_pm_listener(ssk, MPTCP_EVENT_LISTENER_CLOSED);
}

2
net/mptcp/protocol.h
View File

@ -628,7 +628,7 @@ 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);

19
net/mptcp/subflow.c
View File

@ -1791,7 +1791,7 @@ 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;
@ -1840,8 +1840,23 @@ 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);
}