Re: [net] 0b726f6b31: BUG:unable_to_handle_page_fault_for_address

[Willem de Bruijn]

On Mon, Nov 16, 2020 at 8:07 AM Alexander Lobakin <alobakin@xxxxx> wrote:
>
> From: Willem de Bruijn <willemdebruijn.kernel@xxxxxxxxx>
> Date: Fri, 13 Nov 2020 10:51:36 -0500
>
> Hi!
>
> > On Fri, Nov 13, 2020 at 7:00 AM kernel test robot <oliver.sang@xxxxxxxxx> wrote:
> >>
> >>
> >> Greeting,
> >>
> >> FYI, we noticed the following commit (built with gcc-9):
> >>
> >> commit: 0b726f6b318a07644b6c2388e6e44406740f4754 ("[PATCH v3 net] net: udp: fix Fast/frag0 UDP GRO")
> >> url: https://github.com/0day-ci/linux/commits/Alexander-Lobakin/net-udp-fix-Fast-frag0-UDP-GRO/20201110-052215
> >> base: https://git.kernel.org/cgit/linux/kernel/git/davem/net.git 4e0396c59559264442963b349ab71f66e471f84d
> >>
> >> in testcase: apachebench
> >> version:
> >> with following parameters:
> >>
> >>         runtime: 300s
> >>         concurrency: 2000
> >>         cluster: cs-localhost
> >>         cpufreq_governor: performance
> >>         ucode: 0x7000019
> >>
> >> test-description: apachebench is a tool for benchmarking your Apache Hypertext Transfer Protocol (HTTP) server.
> >> test-url: https://httpd.apache.org/docs/2.4/programs/ab.html
> >>
> >>
> >> on test machine: 16 threads Intel(R) Xeon(R) CPU D-1541 @ 2.10GHz with 48G memory
> >>
> >> caused below changes (please refer to attached dmesg/kmsg for entire log/backtrace):
> >>
> >>
> >> If you fix the issue, kindly add following tag
> >> Reported-by: kernel test robot <oliver.sang@xxxxxxxxx>
> >>
> >>
> >> [   28.582714] BUG: unable to handle page fault for address: fffffffffffffffa
> >> [   28.590164] #PF: supervisor read access in kernel mode
> >> [   28.590164] #PF: error_code(0x0000) - not-present page
> >> [   28.590165] PGD c7e20d067 P4D c7e20d067 PUD c7e20f067 PMD 0
> >> [   28.590169] Oops: 0000 [#1] SMP PTI
> >> [   28.590171] CPU: 15 PID: 0 Comm: swapper/15 Not tainted 5.10.0-rc2-00373-g0b726f6b318a #1
> >> [   28.590172] Hardware name: Supermicro SYS-5018D-FN4T/X10SDV-8C-TLN4F, BIOS 1.1 03/02/2016
> >> [   28.590177] RIP: 0010:__udp4_lib_rcv+0x547/0xbe0
> >> [   28.590178] Code: 74 0a f6 45 3c 80 74 04 44 8b 4d 28 48 8b 55 58 48 83 e2 fe 74 07 8b 52 7c 85 d2 75 06 8b 95 90 00 00 00 48 8b be f0 04 00 00 <44> 8b 58 0c 8b 48 10 55 41 55 44 89 de 41 51 41 89 d1 44 89 d2 e8
> >> [   28.590179] RSP: 0018:ffffc900003b4bb8 EFLAGS: 00010246
> >> [   28.590180] RAX: ffffffffffffffee RBX: 0000000000000011 RCX: ffff888c7bc580e2
> >> [   28.590181] RDX: 0000000000000002 RSI: ffff88810ddc8000 RDI: ffffffff82d68f00
> >> [   28.590182] RBP: ffff888c7bf8f800 R08: 00000000000003b7 R09: 0000000000000000
> >> [   28.590182] R10: 0000000000003500 R11: 0000000000000000 R12: ffff888c7bc580e2
> >> [   28.590183] R13: ffffffff82e072b0 R14: ffffffff82d68f00 R15: 0000000000000034
> >> [   28.590184] FS:  0000000000000000(0000) GS:ffff888c7fdc0000(0000) knlGS:0000000000000000
> >> [   28.590185] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
> >> [   28.590186] CR2: fffffffffffffffa CR3: 0000000c7e20a006 CR4: 00000000003706e0
> >> [   28.590186] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000
> >> [   28.590187] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400
> >> [   28.590187] Call Trace:
> >> [   28.590189]  <IRQ>
> >> [   28.590193]  ip_protocol_deliver_rcu+0xc5/0x1c0
> >> [   28.590196]  ip_local_deliver_finish+0x4b/0x60
> >> [   28.738714]  ip_local_deliver+0x6e/0x140
> >> [   28.738717]  ip_sublist_rcv_finish+0x57/0x80
> >> [   28.738719]  ip_sublist_rcv+0x199/0x240
> >> [   28.750730]  ip_list_rcv+0x13a/0x160
> >> [   28.750733]  __netif_receive_skb_list_core+0x2a9/0x2e0
> >> [   28.750736]  netif_receive_skb_list_internal+0x1d3/0x320
> >> [   28.764743]  gro_normal_list+0x19/0x40
> >> [   28.764747]  napi_complete_done+0x68/0x160
> >> [   28.773197]  igb_poll+0x63/0x320
> >> [   28.773198]  net_rx_action+0x136/0x3a0
> >> [   28.773201]  __do_softirq+0xe1/0x2c3
> >> [   28.773204]  asm_call_irq_on_stack+0x12/0x20
> >> [   28.773205]  </IRQ>
> >> [   28.773208]  do_softirq_own_stack+0x37/0x40
> >> [   28.773211]  irq_exit_rcu+0xd2/0xe0
> >> [   28.773213]  common_interrupt+0x74/0x140
> >> [   28.773216]  asm_common_interrupt+0x1e/0x40
> >> [   28.773219] RIP: 0010:cpuidle_enter_state+0xd2/0x360
> >
> > This was expected. This v3 of the patch has already been superseded by
> > one that addresses this lookup:
>
> Wait. This page fault happens on IP receive, which is performed after
> all GRO processing. At this point, all headers are pulled to skb->head,
> and no GRO helpers are needed to access them.
> The function that causes that, __udp4_lib_rcv(), uses ip_hdr() a lot,
> and it's safe. There should be another questionable point.

Right, patch v3 calls skb_gro_network_header from
__udp4_lib_lookup_skb, which is called from __udp4_lib_rcv, the
function at which the crash is reported.

@@ -534,7 +534,7 @@ static inline struct sock
*__udp4_lib_lookup_skb(struct sk_buff *skb,
                                                 __be16 sport, __be16 dport,
                                                 struct udp_table *udptable)
 {
-       const struct iphdr *iph = ip_hdr(skb);
+       const struct iphdr *iph = skb_gro_network_header(skb);