netdev - Re: [PATCHv3] netem: Segment GSO packets on enqueue

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Date:	Sat, 30 Apr 2016 09:30:53 -0400
From:	Neil Horman <nhorman@...driver.com>
To:	Stephen Hemminger <stephen@...workplumber.org>
Cc:	netdev@...r.kernel.org, Jamal Hadi Salim <jhs@...atatu.com>,
	"David S. Miller" <davem@...emloft.net>,
	netem@...ts.linux-foundation.org, eric.dumazet@...il.com
Subject: Re: [PATCHv3] netem: Segment GSO packets on enqueue

On Fri, Apr 29, 2016 at 11:19:05AM -0700, Stephen Hemminger wrote:
> On Fri, 29 Apr 2016 13:35:48 -0400
> Neil Horman <nhorman@...driver.com> wrote:
> 
> > 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 whcih this applies
> > 
> > Signed-off-by: Neil Horman <nhorman@...driver.com>
> > CC: Jamal Hadi Salim <jhs@...atatu.com>
> > CC: "David S. Miller" <davem@...emloft.net>
> > CC: netem@...ts.linux-foundation.org
> > CC: eric.dumazet@...il.com
> > 
> 
> This looks like a good idea.
> 
> Please cleanup the formatting issues:
> 
> This was recently reported to me, and reproduced on the latest net kernel, when
> 
> WARNING: 'whcih' may be misspelled - perhaps 'which'?
> #93: 
> tested successfully by myself on the latest net kernel, to whcih this applies
> 
> ERROR: "foo* bar" should be "foo *bar"
> #130: FILE: net/sched/sch_netem.c:402:
> +static struct sk_buff* netem_segment(struct sk_buff *skb, struct Qdisc *sch)
> 
> 
> CHECK: braces {} should be used on all arms of this statement
> #164: FILE: net/sched/sch_netem.c:479:
> +		if (skb_is_gso(skb)) {
> [...]
> +		} else
> [...]
> 
> CHECK: braces {} should be used on all arms of this statement
> #198: FILE: net/sched/sch_netem.c:562:
> +			if (rc != NET_XMIT_SUCCESS) {
> [...]
> +			} else
> [...]
> 
> 
> 
> 
> 
> 
Will, do when I get back to the office monday
Thanks!
Neil