On Tue, Mar 19, 2024 at 09:59:48PM +0000, Trond Myklebust wrote:
> On Tue, 2024-03-19 at 16:07 -0400, Josef Bacik wrote:
> > We've been seeing variations of the following panic in production
> >
> > BUG: kernel NULL pointer dereference, address: 0000000000000000
> > RIP: 0010:ip6_pol_route+0x59/0x7a0
> > Call Trace:
> > <IRQ>
> > ? __die+0x78/0xc0
> > ? page_fault_oops+0x286/0x380
> > ? fib6_table_lookup+0x95/0xf40
> > ? exc_page_fault+0x5d/0x110
> > ? asm_exc_page_fault+0x22/0x30
> > ? ip6_pol_route+0x59/0x7a0
> > ? unlink_anon_vmas+0x370/0x370
> > fib6_rule_lookup+0x56/0x1b0
> > ? update_blocked_averages+0x2c6/0x6a0
> > ip6_route_output_flags+0xd2/0x130
> > ip6_dst_lookup_tail+0x3b/0x220
> > ip6_dst_lookup_flow+0x2c/0x80
> > inet6_sk_rebuild_header+0x14c/0x1e0
> > ? tcp_release_cb+0x150/0x150
> > __tcp_retransmit_skb+0x68/0x6b0
> > ? tcp_current_mss+0xca/0x150
> > ? tcp_release_cb+0x150/0x150
> > tcp_send_loss_probe+0x8e/0x220
> > tcp_write_timer+0xbe/0x2d0
> > run_timer_softirq+0x272/0x840
> > ? hrtimer_interrupt+0x2c9/0x5f0
> > ? sched_clock_cpu+0xc/0x170
> > irq_exit_rcu+0x171/0x330
> > sysvec_apic_timer_interrupt+0x6d/0x80
> > </IRQ>
> > <TASK>
> > asm_sysvec_apic_timer_interrupt+0x16/0x20
> > RIP: 0010:cpuidle_enter_state+0xe7/0x243
> >
> > Inspecting the vmcore with drgn you can see why this is a NULL
> > pointer deref
> >
> > >>> prog.crashed_thread().stack_trace()[0]
> > #0 at 0xffffffff810bfa89 (ip6_pol_route+0x59/0x796) in
> > ip6_pol_route at net/ipv6/route.c:2212:40
> >
> > 2212 if (net->ipv6.devconf_all->forwarding == 0)
> > 2213 strict |= RT6_LOOKUP_F_REACHABLE;
> >
> > >>>
> > prog.crashed_thread().stack_trace()[0]['net'].ipv6.devconf_all
> > (struct ipv6_devconf *)0x0
> >
> > Looking at the socket you can see that it's been closed
> >
> > >>>
> > decode_enum_type_flags(prog.crashed_thread().stack_trace()[11]['sk'].
> > __sk_common.skc_flags, prog.type('enum sock_flags'))
> > 'SOCK_DEAD|SOCK_KEEPOPEN|SOCK_ZAPPED|SOCK_USE_WRITE_QUEUE'
> > >>> decode_enum_type_flags(1 <<
> > prog.crashed_thread().stack_trace()[11]['sk'].__sk_common.skc_state.v
> > alue_(), prog["TCPF_CLOSE"].type_, bit_numbers=False)
> > 'TCPF_FIN_WAIT1'
> >
> > This occurs in our container setup where we have an NFS mount that
> > belongs to the containers network namespace. On container shutdown
> > our
> > netns goes away, which sets net->ipv6.defconf_all = NULL, and then we
> > panic. In the kernel we're responsible for destroying our sockets
> > when
> > the network namespace exits, or holding a reference on the network
> > namespace for our sockets so this doesn't happen.
> >
> > Even once we shutdown the socket we can still have TCP timers that
> > fire
> > in the background, hence this panic. SUNRPC shuts down the socket
> > and
> > throws away all knowledge of it, but it's still doing things in the
> > background.
> >
> > Fix this by grabbing a reference on the network namespace for any tcp
> > sockets we open. With this patch I'm able to cycle my 500 node
> > stress
> > tier over and over again without panicing, whereas previously I was
> > losing 10-20 nodes every shutdown cycle.
> >
> > Signed-off-by: Josef Bacik <josef@xxxxxxxxxxxxxx>
> > ---
> > Apologies, I just grepped for SUNRPC in MAINTAINERS and didn't
> > realize there was
> > a division of the client and server side of SUNRPC.
> >
> > net/sunrpc/xprtsock.c | 20 ++++++++++++++++++++
> > 1 file changed, 20 insertions(+)
> >
> > diff --git a/net/sunrpc/xprtsock.c b/net/sunrpc/xprtsock.c
> > index bb81050c870e..f02387751a94 100644
> > --- a/net/sunrpc/xprtsock.c
> > +++ b/net/sunrpc/xprtsock.c
> > @@ -2333,6 +2333,7 @@ static int xs_tcp_finish_connecting(struct
> > rpc_xprt *xprt, struct socket *sock)
> >
> > if (!transport->inet) {
> > struct sock *sk = sock->sk;
> > + struct net *net = sock_net(sk);
> >
> > /* Avoid temporary address, they are bad for long-
> > lived
> > * connections such as NFS mounts.
> > @@ -2350,7 +2351,26 @@ static int xs_tcp_finish_connecting(struct
> > rpc_xprt *xprt, struct socket *sock)
> > tcp_sock_set_nodelay(sk);
> >
> > lock_sock(sk);
> > + /*
> > + * Because timers can fire after the fact we need to
> > hold a
> > + * reference on the netns for this socket.
> > + */
> > + if (!sk->sk_net_refcnt) {
> > + if (!maybe_get_net(net)) {
> > + release_sock(sk);
> > + return -ENOTCONN;
> > + }
> > + /*
> > + * For kernel sockets we have a tracker put
> > in place for
> > + * the tracing, we need to free this to
> > maintaine
> > + * consistent tracking info.
> > + */
> > + __netns_tracker_free(net, &sk->ns_tracker,
> > false);
> >
> > + sk->sk_net_refcnt = 1;
> > + netns_tracker_alloc(net, &sk->ns_tracker,
> > GFP_KERNEL);
> > + sock_inuse_add(net, 1);
> > + }
> > xs_save_old_callbacks(transport, sk);
> >
> > sk->sk_user_data = xprt;
>
> Hmm... Doesn't this end up being more or less equivalent to calling
> __sock_create() with the kernel flag being set to 0?
AFAICT yes, but there are a lot of other things that happen with kern being set
to 1, so I think this is a safer bet, and is analagous to this other fix
3a58f13a881e ("net: rds: acquire refcount on TCP sockets"). Thanks,
Josef
