Date:	Mon, 11 Aug 2014 19:37:06 +0400
From:	Andrew Vagin <avagin@...allels.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
CC:	Andrey Wagin <avagin@...il.com>,
	"criu@...nvz.org" <criu@...nvz.org>, <netdev@...r.kernel.org>,
	Pavel Emelyanov <xemul@...allels.com>
Subject: Re: [CRIU] linux-next: WARNING: CPU: 0 PID: 2825 at
 net/ipv4/tcp_input.c:3078 tcp_ack+0x11f5/0x1380()

On Mon, Aug 11, 2014 at 04:12:32PM +0200, Eric Dumazet wrote:
> On Mon, 2014-08-11 at 17:35 +0400, Andrey Wagin wrote:
> > Hi All,
> > 
> > I execute CRIU tests on linux-next. Today I started to check the tain
> > flag and found a warning:
> > 
> > [  866.469685] Peer 127.0.0.1:46524/8880 unexpectedly shrunk window
> > 2532634294:2557500938 (repaired)
> > [  879.562534] ------------[ cut here ]------------
> > [  879.562947] WARNING: CPU: 0 PID: 2825 at net/ipv4/tcp_input.c:3078
> > tcp_ack+0x11f5/0x1380()
> > [  879.563571] Modules linked in: tun netlink_diag af_packet_diag
> > udp_diag tcp_diag inet_diag unix_diag ip6t_rpfilter ip6t_REJECT
> > xt_conntrack cfg80211 rfkill ebtable_nat ebtable_broute bridge stp llc
> > ebtable_filter ebtables ppdev ip6table_nat nf_conntrack_ipv6
> > nf_defrag_ipv6 nf_nat_ipv6 ip6table_mangle ip6table_security
> > ip6table_raw ip6table_filter ip6_tables iptable_nat nf_conntrack_ipv4
> > nf_defrag_ipv4 nf_nat_ipv4 nf_nat nf_conntrack iptable_mangle
> > iptable_security iptable_raw microcode serio_raw i2c_piix4 parport_pc
> > parport nfsd auth_rpcgss nfs_acl lockd sunrpc virtio_blk virtio_net
> > virtio_pci virtio_ring virtio ata_generic pata_acpi
> > [  879.567253] CPU: 0 PID: 2825 Comm: socket-tcpbuf-l Not tainted
> > 3.16.0-next-20140811 #1
> > [  879.567829] Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
> > [  879.568177]  0000000000000000 00000000c532680c ffff880039643d00
> > ffffffff817aa2d2
> > [  879.568776]  0000000000000000 ffff880039643d38 ffffffff8109afbd
> > ffff880039d6ba80
> > [  879.569386]  ffff88003a449800 000000002983d6bd 0000000000000000
> > 000000002983d6bc
> > [  879.569982] Call Trace:
> > [  879.570264]  [<ffffffff817aa2d2>] dump_stack+0x4d/0x66
> > [  879.570599]  [<ffffffff8109afbd>] warn_slowpath_common+0x7d/0xa0
> > [  879.570935]  [<ffffffff8109b0ea>] warn_slowpath_null+0x1a/0x20
> > [  879.571292]  [<ffffffff816d0a05>] tcp_ack+0x11f5/0x1380
> > [  879.571614]  [<ffffffff816d10bd>] tcp_rcv_established+0x1ed/0x710
> > [  879.571958]  [<ffffffff816dc9da>] tcp_v4_do_rcv+0x10a/0x370
> > [  879.572315]  [<ffffffff81657459>] release_sock+0x89/0x1d0
> > [  879.572642]  [<ffffffff816c81a0>] do_tcp_setsockopt.isra.36+0x120/0x860
> > [  879.573000]  [<ffffffff8110a52e>] ? rcu_read_lock_held+0x6e/0x80
> > [  879.573352]  [<ffffffff816c8912>] tcp_setsockopt+0x32/0x40
> > [  879.573678]  [<ffffffff81654ac4>] sock_common_setsockopt+0x14/0x20
> > [  879.574031]  [<ffffffff816537b0>] SyS_setsockopt+0x80/0xf0
> > [  879.574393]  [<ffffffff817b40a9>] system_call_fastpath+0x16/0x1b
> > [  879.574730] ---[ end trace a17cbc38eb8c5c00 ]---
> > [  893.880049] Peer 0000:0000:0000:0000:0000:0000:0000:0001:60450/8880
> > unexpectedly shrunk window 6341700:31207524 (repaired)
> > 
> > During tests a few tcp connections have been repaired. I think the
> > problem is around these sockets. I'm going to look what wrong here.
> > --
> 
> Hmmff
> 
> net/ipv4/tcp.c at line 1195 should be updated I guess.

Yes. We need to initialize skb->skb_mstamp here. Thanks.

> 
> Although I do not really understand the logic here.
> 
> If we do not have a valid timestamp on repair, why force using current
> time ?
> 
> It breaks rtt estimations.

Yes, it does. We hope that tcp code will fix rtt according with next
packages.

ps: Add Pavel in CC.

> 
> 
> 
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