Re: [patch added to 3.12-stable] netem: Segment GSO packets on enqueue

[Jiri Slaby <jslaby@suse.cz>]

On 05/18/2016, 04:54 PM, Eric Dumazet wrote:
> On Wed, 2016-05-18 at 16:44 +0200, Jiri Slaby wrote:
>> From: Neil Horman <nhorman@tuxdriver.com>
>>
>> This patch has been added to the 3.12 stable tree. If you have any
>> objections, please let us know.
>>
>> ===============
>>
>> [ Upstream commit 6071bd1aa13ed9e41824bafad845b7b7f4df5cfd ]
>>
>> This was recently reported to me, and reproduced on the latest net kernel,
>> when attempting to run netperf from a host that had a netem qdisc attached
>> to the egress interface:
>>
>> [  788.073771] ---------------------[ cut here ]---------------------------
>> [  788.096716] WARNING: at net/core/dev.c:2253 skb_warn_bad_offload+0xcd/0xda()
>> [  788.129521] bnx2: caps=(0x00000001801949b3, 0x0000000000000000) len=2962
>> data_len=0 gso_size=1448 gso_type=1 ip_summed=3
>> [  788.182150] Modules linked in: sch_netem kvm_amd kvm crc32_pclmul ipmi_ssif
>> ghash_clmulni_intel sp5100_tco amd64_edac_mod aesni_intel lrw gf128mul
>> glue_helper ablk_helper edac_mce_amd cryptd pcspkr sg edac_core hpilo ipmi_si
>> i2c_piix4 k10temp fam15h_power hpwdt ipmi_msghandler shpchp acpi_power_meter
>> pcc_cpufreq nfsd auth_rpcgss nfs_acl lockd grace sunrpc ip_tables xfs libcrc32c
>> sd_mod crc_t10dif crct10dif_generic mgag200 syscopyarea sysfillrect sysimgblt
>> i2c_algo_bit drm_kms_helper ahci ata_generic pata_acpi ttm libahci
>> crct10dif_pclmul pata_atiixp tg3 libata crct10dif_common drm crc32c_intel ptp
>> serio_raw bnx2 r8169 hpsa pps_core i2c_core mii dm_mirror dm_region_hash dm_log
>> dm_mod
>> [  788.465294] CPU: 16 PID: 0 Comm: swapper/16 Tainted: G        W
>> ------------   3.10.0-327.el7.x86_64 #1
>> [  788.511521] Hardware name: HP ProLiant DL385p Gen8, BIOS A28 12/17/2012
>> [  788.542260]  ffff880437c036b8 f7afc56532a53db9 ffff880437c03670
>> ffffffff816351f1
>> [  788.576332]  ffff880437c036a8 ffffffff8107b200 ffff880633e74200
>> ffff880231674000
>> [  788.611943]  0000000000000001 0000000000000003 0000000000000000
>> ffff880437c03710
>> [  788.647241] Call Trace:
>> [  788.658817]  <IRQ>  [<ffffffff816351f1>] dump_stack+0x19/0x1b
>> [  788.686193]  [<ffffffff8107b200>] warn_slowpath_common+0x70/0xb0
>> [  788.713803]  [<ffffffff8107b29c>] warn_slowpath_fmt+0x5c/0x80
>> [  788.741314]  [<ffffffff812f92f3>] ? ___ratelimit+0x93/0x100
>> [  788.767018]  [<ffffffff81637f49>] skb_warn_bad_offload+0xcd/0xda
>> [  788.796117]  [<ffffffff8152950c>] skb_checksum_help+0x17c/0x190
>> [  788.823392]  [<ffffffffa01463a1>] netem_enqueue+0x741/0x7c0 [sch_netem]
>> [  788.854487]  [<ffffffff8152cb58>] dev_queue_xmit+0x2a8/0x570
>> [  788.880870]  [<ffffffff8156ae1d>] ip_finish_output+0x53d/0x7d0
>> ...
>>
>> The problem occurs because netem is not prepared to handle GSO packets (as it
>> uses skb_checksum_help in its enqueue path, which cannot manipulate these
>> frames).
>>
>> The solution I think is to simply segment the skb in a simmilar fashion to the
>> way we do in __dev_queue_xmit (via validate_xmit_skb), with some minor changes.
>> When we decide to corrupt an skb, if the frame is GSO, we segment it, corrupt
>> the first segment, and enqueue the remaining ones.
>>
>> tested successfully by myself on the latest net kernel, to which this applies
>>
>> [js] backport to 3.12: no qdisc_qstats_drop yet, update directly
> 
> ... But qdisc_tree_reduce_backlog() was not there in 3.12

Yeah, but I pulled the series from net_41 including the
qdisc_tree_reduce_backlog backport.

>> +		if (nb > 1)
>> +			qdisc_tree_reduce_backlog(sch, 1 - nb, prev_len - len);
>> +	}
>>  	return NET_XMIT_SUCCESS;
>>  }

thanks,
-- 
js
suse labs