netdev - Re: [PATCH net v2] tcp: Force updating pcount after skb

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Date:	Tue, 09 Jun 2015 10:06:25 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Martin KaFai Lau <kafai@...com>
Cc:	netdev <netdev@...r.kernel.org>, Kernel Team <kernel-team@...com>,
	Grant Zhang <gzhang@...tly.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Neal Cardwell <ncardwell@...gle.com>,
	Yuchung Cheng <ycheng@...gle.com>
Subject: Re: [PATCH net v2] tcp: Force updating pcount after skb_pull()
 during mtu probing

On Mon, 2015-06-08 at 11:11 -0700, Eric Dumazet wrote:
> On Mon, 2015-06-08 at 10:58 -0700, Martin KaFai Lau wrote:
> 
> > It seems the invariant does not hold at this point also.
> > Should the invariant fix be something for net-next? or Would you like
> > to post a patch for it?
> 
> This patch definitely can target net-next, it is not a new regression.
> 
> Once fully tested, we can ask David to submit a stable version later.
> 
> Yes, I can provide a v3, probably at the end of today.

I've been working on this, but still can get the bug triggering in
tcp_fragment(), no matter what (Neal patch , yours, mine...)

I suspect a problem in skb_shift() or tcp_shifted_skb() and am doing
additional tests.

[ 1806.206345] ------------[ cut here ]------------
[ 1806.206359] WARNING: CPU: 19 PID: 0 at net/ipv4/tcp_output.c:1159 tcp_fragment+0x2b0/0x2d0()
[ 1806.206360] Modules linked in: ip_gre gre sit ip_tunnel tunnel4 bonding w1_therm wire cdc_acm ehci_pci ehci_hcd i2c_dev i2c_i801 i2c_core msr cpuid ib_uverbs mlx4_ib ib_sa ib_mad ib_core ib_addr ip6table_mangle ip6_tables ipv6
[ 1806.206376] CPU: 19 PID: 0 Comm: swapper/19 Tainted: G        W       4.1.0-smp-DEV #1762
[ 1806.206378]  ffffffff8196ba4b ffff88407fae38f8 ffffffff81643125 00000000000000dd
[ 1806.206380]  0000000000000000 ffff88407fae3938 ffffffff810a8c97 ffff88407fae3998
[ 1806.206382]  ffff883f75498200 ffff881fe1d5f800 000000000000000d 0000000000004802
[ 1806.206384] Call Trace:
[ 1806.206385]  <IRQ>  [<ffffffff81643125>] dump_stack+0x45/0x57
[ 1806.206395]  [<ffffffff810a8c97>] warn_slowpath_common+0x97/0xe0
[ 1806.206396]  [<ffffffff810a8cfa>] warn_slowpath_null+0x1a/0x20
[ 1806.206398]  [<ffffffff815df0c0>] tcp_fragment+0x2b0/0x2d0
[ 1806.206400]  [<ffffffff815d62e1>] tcp_mark_head_lost+0x191/0x280
[ 1806.206402]  [<ffffffff815d641d>] tcp_update_scoreboard+0x4d/0x80
[ 1806.206404]  [<ffffffff815daa24>] tcp_fastretrans_alert+0x6e4/0xc20
[ 1806.206406]  [<ffffffff815dbcef>] tcp_ack+0xb0f/0x13c0
[ 1806.206408]  [<ffffffff815dcc31>] tcp_rcv_established+0x311/0x820
[ 1806.206410]  [<ffffffff815e79cb>] tcp_v4_do_rcv+0x14b/0x3d0
[ 1806.206414]  [<ffffffff812f15e6>] ? security_sock_rcv_skb+0x16/0x20
[ 1806.206415]  [<ffffffff815e8e46>] tcp_v4_rcv+0x8c6/0x9d0
[ 1806.206418]  [<ffffffff815c1dec>] ip_local_deliver_finish+0xac/0x230
[ 1806.206419]  [<ffffffff815c216a>] ip_local_deliver+0xaa/0xc0
[ 1806.206421]  [<ffffffff815c1d40>] ? ip_rcv_finish+0x380/0x380
[ 1806.206422]  [<ffffffff815c1a48>] ip_rcv_finish+0x88/0x380
[ 1806.206423]  [<ffffffff815c2487>] ip_rcv+0x307/0x420
[ 1806.206426]  [<ffffffff815c19c0>] ? inet_add_protocol+0x50/0x50
[ 1806.206431]  [<ffffffff8157cc0c>] __netif_receive_skb_core+0x5bc/0xa30
[ 1806.206432]  [<ffffffff8157d0a6>] __netif_receive_skb+0x26/0x70
[ 1806.206434]  [<ffffffff8157d180>] process_backlog+0x90/0x130
[ 1806.206436]  [<ffffffff8157d9a7>] net_rx_action+0x157/0x330
[ 1806.206439]  [<ffffffff810ac9c7>] __do_softirq+0xe7/0x270
[ 1806.206441]  [<ffffffff810acd85>] irq_exit+0xa5/0xb0
[ 1806.206445]  [<ffffffff8108aa65>] smp_call_function_single_interrupt+0x35/0x40
[ 1806.206448]  [<ffffffff8164ae2b>] call_function_single_interrupt+0x6b/0x70



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