[MPTCP] Re: [MPTCP][PATCH v7 mptcp-next 1/7] mptcp: create the listening socket for new port

[Paolo Abeni <pabeni at redhat.com>]

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Hello,

On Mon, 2020-12-07 at 14:30 +0800, Geliang Tang wrote:
> On Thu, Dec 03, 2020 at 05:36:08PM -0800, Mat Martineau wrote:
> > On Mon, 30 Nov 2020, Geliang Tang wrote:
> > 
> > > This patch created a listening socket when an address with a port-number
> > > is added by PM netlink. Then binded the new port to the socket, and
> > > listened for the connection.
> > > 
> > > Signed-off-by: Geliang Tang <geliangtang(a)gmail.com>
> > > ---
> > > net/mptcp/pm_netlink.c | 58 ++++++++++++++++++++++++++++++++++++++++++
> > > net/mptcp/protocol.c   |  2 +-
> > > net/mptcp/protocol.h   |  3 +++
> > > net/mptcp/subflow.c    |  4 +--
> > > 4 files changed, 64 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/net/mptcp/pm_netlink.c b/net/mptcp/pm_netlink.c
> > > index 5151cfcd6962..c296927bf167 100644
> > > --- a/net/mptcp/pm_netlink.c
> > > +++ b/net/mptcp/pm_netlink.c
> > > @@ -26,6 +26,7 @@ struct mptcp_pm_addr_entry {
> > > 	struct list_head	list;
> > > 	struct mptcp_addr_info	addr;
> > > 	struct rcu_head		rcu;
> > > +	struct socket		*lsk;
> > 
> > Two things to fix up:
> > 
> > Non-zero lsk is not released everywhere mptcp_pm_addr_entry structs are
> > freed.
> > 
> > lsk is not initialized in mptcp_pm_nl_get_local_id()
> > 
> > > };
> > > 
> > > struct mptcp_pm_add_entry {
> > > @@ -732,6 +733,53 @@ static struct pm_nl_pernet *genl_info_pm_nl(struct genl_info *info)
> > > 	return net_generic(genl_info_net(info), pm_nl_pernet_id);
> > > }
> > > 
> > > +static int mptcp_pm_nl_create_listen_socket(struct sock *sk,
> > > +					    struct mptcp_pm_addr_entry *entry)
> > > +{
> > > +	struct sockaddr_storage addr;
> > > +	struct mptcp_sock *msk;
> > > +	struct socket *ssock;
> > > +	int backlog = 20;
> > 
> > Any comment on the choice of '20' here? Could it be too small for a high
> > connection rate, or worth a sysctl?
> > 
> > Thanks,
> > 
> > Mat
> > 
> > > +	int err;
> > > +
> > > +	err = sock_create_kern(sock_net(sk), entry->addr.family,
> > > +			       SOCK_STREAM, IPPROTO_MPTCP, &entry->lsk);
> > > +	if (err)
> > > +		return err;
> > > +
> > > +	msk = mptcp_sk(entry->lsk->sk);
> > > +	if (!msk) {
> > > +		err = -EINVAL;
> > > +		goto out;
> > > +	}
> > > +
> > > +	ssock = __mptcp_nmpc_socket(msk);
> > > +	if (!ssock) {
> > > +		err = -EINVAL;
> > > +		goto out;
> > > +	}
> > > +
> > > +	mptcp_info2sockaddr(&entry->addr, &addr);
> > > +	err = kernel_bind(ssock, (struct sockaddr *)&addr,
> > > +			  sizeof(struct sockaddr_in));
> > > +	if (err) {
> > > +		pr_warn("kernel_bind error, err=%d", err);
> > > +		goto out;
> > > +	}
> > > +
> > > +	err = kernel_listen(ssock, backlog);
> > > +	if (err) {
> > > +		pr_warn("kernel_listen error, err=%d", err);
> > > +		goto out;
> > > +	}
> > > +
> > > +	return 0;
> > > +
> > > +out:
> > > +	sock_release(entry->lsk);
> 
> I need some help about releasing the MPTCP type listening socket. When I
> use "sock_release(entry->lsk)" to release it, I'll get a deadlock warning
> like this:
> 
> ----
> 
> [   55.789592] ============================================
> [   55.789593] WARNING: possible recursive locking detected
> [   55.789594] 5.10.0-rc6-mptcp+ #742 Not tainted
> [   55.789595] --------------------------------------------
> [   55.789596] pm_nl_ctl/5583 is trying to acquire lock:
> [   55.789597] ffff9ff9883cb960 (k-sk_lock-AF_INET){+.+.}-{0:0}, at: __mptcp_close_ssk+0x52/0x160
> [   55.789604]
>                but task is already holding lock:
> [   55.789605] ffff9ff949c1c1a0 (k-sk_lock-AF_INET){+.+.}-{0:0}, at: mptcp_close+0x45/0x320
> [   55.789608]
>                other info that might help us debug this:
> [   55.789609]  Possible unsafe locking scenario:
> 
> [   55.789610]        CPU0
> [   55.789610]        ----
> [   55.789611]   lock(k-sk_lock-AF_INET);
> [   55.789613]   lock(k-sk_lock-AF_INET);
> [   55.789614]
>                 *** DEADLOCK ***
> 
> [   55.789615]  May be due to missing lock nesting notation
> 
> [   55.789616] 3 locks held by pm_nl_ctl/5583:
> [   55.789617]  #0: ffffffff8c5f9af0 (cb_lock){++++}-{3:3}, at: genl_rcv+0x15/0x40
> [   55.789621]  #1: ffffffff8c5f9b88 (genl_mutex){+.+.}-{3:3}, at: genl_rcv_msg+0xf5/0x1c0
> [   55.789625]  #2: ffff9ff949c1c1a0 (k-sk_lock-AF_INET){+.+.}-{0:0}, at: mptcp_close+0x45/0x320
> [   55.789629]
>                stack backtrace:
> [   55.789631] CPU: 1 PID: 5583 Comm: pm_nl_ctl Kdump: loaded Not tainted 5.10.0-rc6-mptcp+ #742
> [   55.789632] Hardware name: TIMI Mi Laptop Pro 15/TM1905, BIOS XMACM500P0301 04/08/2020
> [   55.789633] Call Trace:
> [   55.789637]  dump_stack+0x8b/0xb0
> [   55.789639]  __lock_acquire.cold+0x159/0x2ab
> [   55.789643]  ? debug_object_assert_init+0x4b/0x130
> [   55.789646]  lock_acquire+0x116/0x370
> [   55.789648]  ? __mptcp_close_ssk+0x52/0x160
> [   55.789651]  ? lock_sock_nested+0x51/0x90
> [   55.789653]  lock_sock_nested+0x70/0x90
> [   55.789655]  ? __mptcp_close_ssk+0x52/0x160
> [   55.789657]  __mptcp_close_ssk+0x52/0x160
> [   55.789659]  __mptcp_destroy_sock+0x119/0x210
> [   55.789661]  mptcp_close+0x281/0x320
> [   55.789663]  inet_release+0x99/0xa8
> [   55.789665]  sock_release+0x20/0x70
> [   55.789667]  mptcp_nl_cmd_add_addr+0x27c/0x2e0
> [   55.789670]  genl_family_rcv_msg_doit+0xcd/0x110
> [   55.789675]  genl_rcv_msg+0xce/0x1c0
> [   55.789677]  ? mptcp_nl_cmd_get_limits+0x260/0x260
> [   55.789680]  ? genl_get_cmd+0xd0/0xd0
> [   55.789683]  netlink_rcv_skb+0x50/0xf0
> [   55.789687]  genl_rcv+0x24/0x40
> [   55.789688]  netlink_unicast+0x16d/0x230
> [   55.789690]  netlink_sendmsg+0x23f/0x460
> [   55.789693]  sock_sendmsg+0x5e/0x60
> [   55.789694]  __sys_sendto+0xf1/0x160
> [   55.789698]  ? do_user_addr_fault+0x215/0x440
> [   55.789701]  ? lockdep_hardirqs_on_prepare+0xff/0x180
> [   55.789702]  __x64_sys_sendto+0x25/0x30
> [   55.789704]  do_syscall_64+0x33/0x40
> [   55.789707]  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> [   55.789709] RIP: 0033:0x7fca52863efa
> [   55.789710] Code: d8 64 89 02 48 c7 c0 ff ff ff ff eb b8 0f 1f 00 f3 0f 1e fa 41 89 ca 64 8b 04 25 18 00 00 00 85 c0 75 15 b8 2c 00 00 00 0f 05 <48> 3d 00 f0 ff ff 77 76 c3 0f 1f 44 00 00 55 48 83 ec 30 44 89 4c
> [   55.789712] RSP: 002b:00007ffc6a45db88 EFLAGS: 00000246 ORIG_RAX: 000000000000002c
> [   55.789714] RAX: ffffffffffffffda RBX: 00007ffc6a45dbf0 RCX: 00007fca52863efa
> [   55.789715] RDX: 0000000000000038 RSI: 00007ffc6a45dbf0 RDI: 0000000000000003
> [   55.789716] RBP: 0000000000000038 R08: 00007ffc6a45db94 R09: 000000000000000c
> [   55.789717] R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000000
> [   55.789718] R13: 0000000000000003 R14: 00007ffc6a45e170 R15: 00007ffc6a45e138
> [   55.789751] MPTCP: msk=000000001cb8c5f2
> [   55.798357] MPTCP: subflow=0000000008e7e757
> 
> ----
> 
> I spent a few days trying to solve this problem, but it didn't go well.
> Please give some suggestions about it, thanks very much.

I'll try to have a look at this tomorrow. I'm sorry, I'm unable to get
there earlier.

Cheers,

Paolo