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Message-ID: <f5167659-99d7-04a1-2175-60ff1dabae71@tessares.net>
Date:   Mon, 13 Mar 2023 15:15:08 +0100
From:   Matthieu Baerts <matthieu.baerts@...sares.net>
To:     Lorenzo Bianconi <lorenzo@...nel.org>, netdev@...r.kernel.org
Cc:     bpf@...r.kernel.org, davem@...emloft.net, edumazet@...gle.com,
        kuba@...nel.org, pabeni@...hat.com, ast@...nel.org,
        daniel@...earbox.net, hawk@...nel.org, john.fastabend@...il.com,
        saeedm@...dia.com, leon@...nel.org, shayagr@...zon.com,
        akiyano@...zon.com, darinzon@...zon.com, sgoutham@...vell.com,
        lorenzo.bianconi@...hat.com, toke@...hat.com, teknoraver@...a.com,
        ttoukan.linux@...il.com
Subject: Re: [PATCH net v2 6/8] veth: take into account device reconfiguration
 for xdp_features flag

Hi Lorenzo,

On 09/03/2023 13:25, Lorenzo Bianconi wrote:
> Take into account tx/rx queues reconfiguration setting device
> xdp_features flag. Moreover consider NETIF_F_GRO flag in order to enable
> ndo_xdp_xmit callback.
> 
> Fixes: 66c0e13ad236 ("drivers: net: turn on XDP features")
> Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>

Thank you for the modification.

Unfortunately, 'git bisect' just told me this modification is the origin
of a new WARN when using veth in a netns:


###################### 8< ######################

=============================
WARNING: suspicious RCU usage
6.3.0-rc1-00144-g064d70527aaa #149 Not tainted
-----------------------------
drivers/net/veth.c:1265 suspicious rcu_dereference_check() usage!

other info that might help us debug this:


rcu_scheduler_active = 2, debug_locks = 1
1 lock held by ip/135:
#0: ffffffff8dc4b108 (rtnl_mutex){+.+.}-{3:3}, at: rtnetlink_rcv_msg
(net/core/rtnetlink.c:6172)

stack backtrace:
CPU: 1 PID: 135 Comm: ip Not tainted 6.3.0-rc1-00144-g064d70527aaa #149
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.15.0-1
04/01/2014
Call Trace:
 <TASK>
dump_stack_lvl (lib/dump_stack.c:107)
lockdep_rcu_suspicious (include/linux/context_tracking.h:152)
veth_set_xdp_features (drivers/net/veth.c:1265 (discriminator 9))
veth_newlink (drivers/net/veth.c:1892)
? veth_set_features (drivers/net/veth.c:1774)
? kasan_save_stack (mm/kasan/common.c:47)
? kasan_save_stack (mm/kasan/common.c:46)
? kasan_set_track (mm/kasan/common.c:52)
? alloc_netdev_mqs (include/linux/slab.h:737)
? rcu_read_lock_sched_held (kernel/rcu/update.c:125)
? trace_kmalloc (include/trace/events/kmem.h:54)
? __xdp_rxq_info_reg (net/core/xdp.c:188)
? alloc_netdev_mqs (net/core/dev.c:10657)
? rtnl_create_link (net/core/rtnetlink.c:3312)
rtnl_newlink_create (net/core/rtnetlink.c:3440)
? rtnl_link_get_net_capable.constprop.0 (net/core/rtnetlink.c:3391)
__rtnl_newlink (net/core/rtnetlink.c:3657)
? lock_downgrade (kernel/locking/lockdep.c:5321)
? rtnl_link_unregister (net/core/rtnetlink.c:3487)
rtnl_newlink (net/core/rtnetlink.c:3671)
rtnetlink_rcv_msg (net/core/rtnetlink.c:6174)
? rtnl_link_fill (net/core/rtnetlink.c:6070)
? mark_usage (kernel/locking/lockdep.c:4914)
? mark_usage (kernel/locking/lockdep.c:4914)
netlink_rcv_skb (net/netlink/af_netlink.c:2574)
? rtnl_link_fill (net/core/rtnetlink.c:6070)
? netlink_ack (net/netlink/af_netlink.c:2551)
? lock_acquire (kernel/locking/lockdep.c:467)
? net_generic (include/linux/rcupdate.h:805)
? netlink_deliver_tap (include/linux/rcupdate.h:805)
netlink_unicast (net/netlink/af_netlink.c:1340)
? netlink_attachskb (net/netlink/af_netlink.c:1350)
netlink_sendmsg (net/netlink/af_netlink.c:1942)
? netlink_unicast (net/netlink/af_netlink.c:1861)
? netlink_unicast (net/netlink/af_netlink.c:1861)
sock_sendmsg (net/socket.c:727)
____sys_sendmsg (net/socket.c:2501)
? kernel_sendmsg (net/socket.c:2448)
? __copy_msghdr (net/socket.c:2428)
___sys_sendmsg (net/socket.c:2557)
? mark_usage (kernel/locking/lockdep.c:4914)
? do_recvmmsg (net/socket.c:2544)
? lock_acquire (kernel/locking/lockdep.c:467)
? find_held_lock (kernel/locking/lockdep.c:5159)
? __lock_release (kernel/locking/lockdep.c:5345)
? __might_fault (mm/memory.c:5625)
? lock_downgrade (kernel/locking/lockdep.c:5321)
? __fget_light (include/linux/atomic/atomic-arch-fallback.h:227)
__sys_sendmsg (include/linux/file.h:31)
? __sys_sendmsg_sock (net/socket.c:2572)
? rseq_get_rseq_cs (kernel/rseq.c:275)
? lockdep_hardirqs_on_prepare.part.0 (kernel/locking/lockdep.c:4263)
do_syscall_64 (arch/x86/entry/common.c:50)
entry_SYSCALL_64_after_hwframe (arch/x86/entry/entry_64.S:120)
RIP: 0033:0x7f0d1aadeb17
Code: 0f 00 f7 d8 64 89 02 48 c7 c0 ff ff ff ff eb b9 0f 1f 00 f3 0f 1e
fa 64 8b 04 25 18 00 00 00 85 c0 75 10 b8 2e 00 00 00 0f 05 <48> 3d 00
f0 ff ff 77 51 c3 48 83 ec 28 89 54 24 1c 48 89 74 24 10
All code
========
   0:   0f 00                   (bad)
   2:   f7 d8                   neg    %eax
   4:   64 89 02                mov    %eax,%fs:(%rdx)
   7:   48 c7 c0 ff ff ff ff    mov    $0xffffffffffffffff,%rax
   e:   eb b9                   jmp    0xffffffffffffffc9
  10:   0f 1f 00                nopl   (%rax)
  13:   f3 0f 1e fa             endbr64
  17:   64 8b 04 25 18 00 00    mov    %fs:0x18,%eax
  1e:   00
  1f:   85 c0                   test   %eax,%eax
  21:   75 10                   jne    0x33
  23:   b8 2e 00 00 00          mov    $0x2e,%eax
  28:   0f 05                   syscall
  2a:*  48 3d 00 f0 ff ff       cmp    $0xfffffffffffff000,%rax
<-- trapping instruction
  30:   77 51                   ja     0x83
  32:   c3                      ret
  33:   48 83 ec 28             sub    $0x28,%rsp
  37:   89 54 24 1c             mov    %edx,0x1c(%rsp)
  3b:   48 89 74 24 10          mov    %rsi,0x10(%rsp)

Code starting with the faulting instruction
===========================================
   0:   48 3d 00 f0 ff ff       cmp    $0xfffffffffffff000,%rax
   6:   77 51                   ja     0x59
   8:   c3                      ret
   9:   48 83 ec 28             sub    $0x28,%rsp
   d:   89 54 24 1c             mov    %edx,0x1c(%rsp)
  11:   48 89 74 24 10          mov    %rsi,0x10(%rsp)
RSP: 002b:00007ffca3305d48 EFLAGS: 00000246 ORIG_RAX: 000000000000002e
RAX: ffffffffffffffda RBX: 00000000640f2bb2 RCX: 00007f0d1aadeb17
RDX: 0000000000000000 RSI: 00007ffca3305db0 RDI: 0000000000000003
RBP: 0000000000000000 R08: 0000000000000001 R09: 00007ffca3304ae0
R10: 0000000000000000 R11: 0000000000000246 R12: 0000000000000001
R13: 00007ffca3305eb4 R14: 00007ffca3305e80 R15: 0000561e28bf5020
 </TASK>
ip (135) used greatest stack depth: 24544 bytes left

###################### 8< ######################


I can reproduce the issue on the "net" tree with just these 3 commands:

# ip netns add ns1
# ip netns add ns2
# ip link add ns1eth1 netns ns1 type veth peer name ns2eth1 netns ns2

Without this commit fccca038f300 ("veth: take into account device
reconfiguration for xdp_features flag"), I don't have the issue.

For more details about the issue detected by CIs validating our MPTCP
tree, including kconfig and vmlinux if needed:

  https://github.com/multipath-tcp/mptcp_net-next/issues/372


Do you mind looking at this regression please? :)


On our side, we will revert this patch in our tree for the moment to
unblock our CI jobs.

Cheers,
Matt
-- 
Tessares | Belgium | Hybrid Access Solutions
www.tessares.net

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