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?
--
Trond Myklebust
Linux NFS client maintainer, Hammerspace
trond.myklebust@xxxxxxxxxxxxxxx
