Date:   Thu, 8 Oct 2020 20:41:51 +0200
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Eric Dumazet <edumazet@...gle.com>
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [Bug 209423] WARN_ON_ONCE() at rtl8169_tso_csum_v2()

On 08.10.2020 19:15, Eric Dumazet wrote:
> On Thu, Oct 8, 2020 at 6:37 PM Heiner Kallweit <hkallweit1@...il.com> wrote:
>>
>> On 02.10.2020 13:48, Eric Dumazet wrote:
>>> On Fri, Oct 2, 2020 at 1:09 PM Heiner Kallweit <hkallweit1@...il.com> wrote:
>>>>
>>>> On 02.10.2020 10:46, Eric Dumazet wrote:
>>>>> On Fri, Oct 2, 2020 at 10:32 AM Eric Dumazet <eric.dumazet@...il.com> wrote:
>>>>>>
>>>>>>
>>>>>>
>>>>>> On 10/2/20 10:26 AM, Eric Dumazet wrote:
>>>>>>> On Thu, Oct 1, 2020 at 10:34 PM Heiner Kallweit <hkallweit1@...il.com> wrote:
>>>>>>>>
>>>>>>>> I have a problem with the following code in ndo_start_xmit() of
>>>>>>>> the r8169 driver. A user reported the WARN being triggered due
>>>>>>>> to gso_size > 0 and gso_type = 0. The chip supports TSO(6).
>>>>>>>> The driver is widely used, therefore I'd expect much more such
>>>>>>>> reports if it should be a common problem. Not sure what's special.
>>>>>>>> My primary question: Is it a valid use case that gso_size is
>>>>>>>> greater than 0, and no SKB_GSO_ flag is set?
>>>>>>>> Any hint would be appreciated.
>>>>>>>>
>>>>>>>>
>>>>>>>
>>>>>>> Maybe this is not a TCP packet ? But in this case GSO should have taken place.
>>>>>>>
>>>>>>> You might add a
>>>>>>> pr_err_once("gso_type=%x\n", shinfo->gso_type);
>>>>>>>
>>>>>
>>>>>>
>>>>>> Ah, sorry I see you already printed gso_type
>>>>>>
>>>>>> Must then be a bug somewhere :/
>>>>>
>>>>>
>>>>> napi_reuse_skb() does :
>>>>>
>>>>> skb_shinfo(skb)->gso_type = 0;
>>>>>
>>>>> It does _not_ clear gso_size.
>>>>>
>>>>> I wonder if in some cases we could reuse an skb while gso_size is not zero.
>>>>>
>>>>> Normally, we set it only from dev_gro_receive() when the skb is queued
>>>>> into GRO engine (status being GRO_HELD)
>>>>>
>>>> Thanks Eric. I'm no expert that deep in the network stack and just wonder
>>>> why napi_reuse_skb() re-initializes less fields in shinfo than __alloc_skb().
>>>> The latter one does a
>>>> memset(shinfo, 0, offsetof(struct skb_shared_info, dataref));
>>>>
>>>
>>> memset() over the whole thing is more expensive.
>>>
>>> Here we know the prior state of some fields, while __alloc_skb() just
>>> got a piece of memory with random content.
>>>
>>>> What I can do is letting the affected user test the following.
>>>>
>>>> diff --git a/net/core/dev.c b/net/core/dev.c
>>>> index 62b06523b..8e75399cc 100644
>>>> --- a/net/core/dev.c
>>>> +++ b/net/core/dev.c
>>>> @@ -6088,6 +6088,7 @@ static void napi_reuse_skb(struct napi_struct *napi, struct sk_buff *skb)
>>>>
>>>>         skb->encapsulation = 0;
>>>>         skb_shinfo(skb)->gso_type = 0;
>>>> +       skb_shinfo(skb)->gso_size = 0;
>>>>         skb->truesize = SKB_TRUESIZE(skb_end_offset(skb));
>>>>         skb_ext_reset(skb);
>>>>
>>>
>>> As I hinted, this should not be needed.
>>>
>>> For debugging purposes, I would rather do :
>>>
>>> BUG_ON(skb_shinfo(skb)->gso_size);
>>>
>>
>> We did the following for debugging:
>>
>> diff --git a/net/core/dev.c b/net/core/dev.c
>> index 62b06523b..4c943b774 100644
>> --- a/net/core/dev.c
>> +++ b/net/core/dev.c
>> @@ -3491,6 +3491,9 @@ static netdev_features_t gso_features_check(const struct sk_buff *skb,
>>  {
>>         u16 gso_segs = skb_shinfo(skb)->gso_segs;
>>
>> +       if (!skb_shinfo(skb)->gso_type)
>> +               skb_warn_bad_offload(skb);
> 
> You also want to get a stack trace here, to give us the call graph.
> 

Here it comes, full story is in https://bugzilla.kernel.org/show_bug.cgi?id=209423


[236222.967498] ------------[ cut here ]------------
[236222.967508] r8169: caps=(0x00000100000041b2, 0x0000000000000000)
[236222.967668] WARNING: CPU: 0 PID: 0 at net/core/dev.c:3184 skb_warn_bad_offload+0x72/0xe0
[236222.967691] Modules linked in: tcp_diag udp_diag raw_diag inet_diag unix_diag tun nft_nat nft_masq nft_objref nf_conntrack_netbios_ns nf_conntrack_broadcast nft_fib_inet nft_fib_ipv4 nft_fib_ipv6 nft_fib nft_reject_inet nf_reject_ipv4 nf_reject_ipv6 nft_reject nft_ct nft_chain_nat ip_set_hash_net ip6table_nat ip6table_mangle ip6table_raw ip6table_security iptable_nat nf_nat nf_conntrack nf_defrag_ipv6 nf_defrag_ipv4 iptable_mangle iptable_raw iptable_security ip_set nf_tables nfnetlink ip6table_filter ip6_tables iptable_filter sunrpc vfat fat snd_hda_codec_realtek snd_hda_codec_generic edac_mce_amd ledtrig_audio kvm_amd snd_hda_codec_hdmi ccp snd_hda_intel snd_intel_dspcfg kvm snd_hda_codec snd_hda_core snd_hwdep irqbypass snd_pcm snd_timer snd hp_wmi sp5100_tco sparse_keymap wmi_bmof fam15h_power k10temp i2c_piix4 soundcore rfkill_gpio rfkill acpi_cpufreq ip_tables xfs amdgpu iommu_v2 gpu_sched i2c_algo_bit ttm drm_kms_helper cec crct10dif_pclmul crc32_pclmul crc32c_intel drm
[236222.967776]  ghash_clmulni_intel ax88179_178a serio_raw usbnet mii r8169 wmi video
[236222.967858] CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.8.12-203.fc32.x86_64 #1
[236222.967870] Hardware name: HP HP t630 Thin Client/8158, BIOS M40 v01.12 02/04/2020
[236222.967895] RIP: 0010:skb_warn_bad_offload+0x72/0xe0
[236222.967908] Code: 8d 95 c8 00 00 00 48 8d 88 e8 01 00 00 48 85 c0 48 c7 c0 d8 d7 15 a4 48 0f 44 c8 4c 89 e6 48 c7 c7 90 7b 47 a4 e8 04 85 72 ff <0f> 0b 5b 5d 41 5c c3 80 7d 00 00 49 c7 c4 3b 28 40 a4 74 ac be 25
[236222.967926] RSP: 0018:ffffa8f9c0003c80 EFLAGS: 00010282
[236222.967938] RAX: 0000000000000034 RBX: ffff8d7090f2cd00 RCX: 0000000000000000
[236222.967951] RDX: ffff8d709b427060 RSI: ffff8d709b418d00 RDI: 0000000000000300
[236222.967962] RBP: ffff8d709a9fc000 R08: 0000000000000406 R09: 0720072007200720
[236222.967974] R10: 0720072007200720 R11: 0729073007300730 R12: ffffffffc012e729
[236222.967986] R13: ffffa8f9c0003d3b R14: 0000000000000000 R15: ffff8d70367652ac
[236222.968000] FS:  0000000000000000(0000) GS:ffff8d709b400000(0000) knlGS:0000000000000000
[236222.968013] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[236222.968023] CR2: 00007f3cf5ebf010 CR3: 0000000113cc6000 CR4: 00000000001406f0
[236222.968035] Call Trace:
[236222.968047]  <IRQ>
[236222.968064]  netif_skb_features+0x25e/0x2c0
[236222.968084]  ? ipt_do_table+0x333/0x600 [ip_tables]
[236222.968098]  validate_xmit_skb+0x1d/0x300
[236222.968111]  validate_xmit_skb_list+0x48/0x70
[236222.968126]  sch_direct_xmit+0x129/0x2f0
[236222.968140]  __dev_queue_xmit+0x710/0x8a0
[236222.968184]  ? nf_confirm+0xcb/0xf0 [nf_conntrack]
[236222.968200]  ? nf_hook_slow+0x3f/0xb0
[236222.968214]  ip_finish_output2+0x2ad/0x560
[236222.968229]  __netif_receive_skb_core+0x4f0/0xf40
[236222.968244]  ? packet_rcv+0x44/0x490
[236222.968257]  __netif_receive_skb_one_core+0x2d/0x70
[236222.968277]  process_backlog+0x96/0x160
[236222.968290]  net_rx_action+0x13c/0x3e0
[236222.968312]  ? usbnet_bh+0x24/0x2b0 [usbnet]
[236222.968327]  __do_softirq+0xd9/0x2c4
[236222.968340]  asm_call_on_stack+0x12/0x20
[236222.968350]  </IRQ>
[236222.968362]  do_softirq_own_stack+0x39/0x50
[236222.968376]  irq_exit_rcu+0xc2/0x100
[236222.968389]  common_interrupt+0x75/0x140
[236222.968405]  asm_common_interrupt+0x1e/0x40
[236222.968427] RIP: 0010:native_safe_halt+0xe/0x10
[236222.968438] Code: 02 20 48 8b 00 a8 08 75 c4 e9 7b ff ff ff cc cc cc cc cc cc cc cc cc cc cc cc cc cc e9 07 00 00 00 0f 00 2d f6 69 49 00 fb f4 <c3> 90 e9 07 00 00 00 0f 00 2d e6 69 49 00 f4 c3 cc cc 0f 1f 44 00
[236222.968456] RSP: 0018:ffffffffa4a03e08 EFLAGS: 00000246
[236222.968467] RAX: 0000000000004000 RBX: 0000000000000001 RCX: 000000000000001f
[236222.968480] RDX: 4ec4ec4ec4ec4ec5 RSI: ffffffffa4b78960 RDI: ffff8d7092f45c00
[236222.968492] RBP: ffff8d709a288000 R08: 0000d6d7f20a4084 R09: 0000000000000006
[236222.968504] R10: 0000000000000022 R11: 000000000000000f R12: ffff8d709a288064
[236222.968515] R13: 0000000000000001 R14: 0000000000000001 R15: 0000000000000000
[236222.968535]  acpi_safe_halt+0x1b/0x30
[236222.968549]  acpi_idle_enter+0x27e/0x2e0
[236222.968566]  cpuidle_enter_state+0x81/0x3f0
[236222.968589]  cpuidle_enter+0x29/0x40
[236222.968602]  do_idle+0x1d5/0x2a0
[236222.968615]  cpu_startup_entry+0x19/0x20
[236222.968628]  start_kernel+0x7f4/0x804
[236222.968645]  secondary_startup_64+0xb6/0xc0
[236222.968659] ---[ end trace 8a4d7f639ad88505 ]---


> 
>> +
>>         if (gso_segs > dev->gso_max_segs)
>>                 return features & ~NETIF_F_GSO_MASK;
>>
>> Following skb then triggered the skb_warn_bad_offload. Not sure whether this helps
>> to find out where in the network stack something goes wrong.
>>
>>
>> [236222.967236] skb len=134 headroom=778 headlen=134 tailroom=31536
>>                 mac=(778,14) net=(792,20) trans=812
>>                 shinfo(txflags=0 nr_frags=0 gso(size=568 type=0 segs=1))
>>                 csum(0x0 ip_summed=1 complete_sw=0 valid=0 level=0)
>>                 hash(0x0 sw=0 l4=0) proto=0x0800 pkttype=0 iif=4
>> [236222.967297] dev name=enp1s0 feat=0x0x00000100000041b2
>> [236222.967392] skb linear:   00000000: 00 13 3b a0 01 e8 7c d3 0a 2d 1b 3b 08 00 45 00
>> [236222.967404] skb linear:   00000010: 00 78 e2 e6 00 00 7b 06 52 e1 d8 3a d0 ce c0 a8
>> [236222.967415] skb linear:   00000020: a0 06 01 bb 8b c6 53 91 be 5e 6e 60 bd e2 80 18
>> [236222.967426] skb linear:   00000030: 01 13 5c f6 00 00 01 01 08 0a 3d d6 6a a3 63 ea
>> [236222.967437] skb linear:   00000040: 5c d9 17 03 03 00 3f af 00 01 84 45 e2 36 e4 6a
>> [236222.967454] skb linear:   00000050: 3d 76 a8 7f d7 12 fa 72 4b d1 d0 74 0d c1 49 77
>> [236222.967466] skb linear:   00000060: 8b a4 bb 04 e5 aa 03 61 d3 e6 1f c9 0d 3e 46 c8
>> [236222.967477] skb linear:   00000070: cd 1f 7d ce e8 a7 84 84 01 5d 1f b4 ee 4f 27 63
>> [236222.967488] skb linear:   00000080: d2 a1 ab 1f 26 1d
>>
>>
>>
>>>
>>> Nothing in GRO stack will change gso_size, unless the packet is queued
>>> by GRO layer (after this, napi_reuse_skb() wont be called)
>>>
>>> napi_reuse_skb() is only used when a packet has been aggregated to
>>> another, and at this point gso_size should be still 0.
>>>
>>

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