[REGRESSION] 5.0-rc2: iptables -nvL consumes 100% of CPU and hogs memory with kernel 5.0-rc2

[Martin Steigerwald <martin@lichtvoll.de>]

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Hi!

Does that ring a bell with someone? For now I just downgraded, no time
for detailed analysis.

Debian bug report at:

iptables -nvL consumes 100% of CPU and hogs memory with kernel 5.0-rc2
https://bugs.debian.org/919325

4.20 works, 5.0-rc2 showed this issue with iptables. Configurations attached.

Excerpt from Debian bug report follows:

I upgraded to self-compiled 5.0-rc2 today and found the machine to be slow
after startup. I saw iptables consuming 100% CPU, it only responded to
SIGKILL. It got restarted several times, probably by some systemd service.

Then I started 'iptables -nvL' manually. And I got this:

% strace -p 5748
[… tons more, in what appeared an endless loop …]
recvmsg(3, {msg_name={sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, msg_namelen=12, msg_iov=[{iov_base={{len=372, type=0xa06 /* NLMSG_??? */, flags=NLM_F_MULTI|0x800, seq=0, pid=5748}, "\x02\x00\x00\x11\x0b\x00\x01\x00\x66\x69\x6c\x74\x65\x72\x00\x00\x0b\x00\x02\x00\x4f\x55\x54\x50\x55\x54\x00\x00\x0c\x00\x03\x00"...}, iov_len=16536}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 372
recvmsg(3, {msg_name={sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, msg_namelen=12, msg_iov=[{iov_base={{len=372, type=0xa06 /* NLMSG_??? */, flags=NLM_F_MULTI|0x800, seq=0, pid=5748}, "\x02\x00\x00\x11\x0b\x00\x01\x00\x66\x69\x6c\x74\x65\x72\x00\x00\x0b\x00\x02\x00\x4f\x55\x54\x50\x55\x54\x00\x00\x0c\x00\x03\x00"...}, iov_len=16536}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 372
recvmsg(3, {msg_name={sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, msg_namelen=12, msg_iov=[{iov_base={{len=372, type=0xa06 /* NLMSG_??? */, flags=NLM_F_MULTI|0x800, seq=0, pid=5748}, "\x02\x00\x00\x11\x0b\x00\x01\x00\x66\x69\x6c\x74\x65\x72\x00\x00\x0b\x00\x02\x00\x4f\x55\x54\x50\x55\x54\x00\x00\x0c\x00\x03\x00"...}, iov_len=16536}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 372
recvmsg(3, ^C{msg_name={sa_family=AF_NETLINK, nl_pid=0, nl_groups=00000000}, msg_namelen=12, msg_iov=[{iov_base={{len=372, type=0xa06 /* NLMSG_??? */, flags=NLM_F_MULTI|0x800, seq=0, pid=5748}, "\x02\x00\x00\x11\x0b\x00\x01\x00\x66\x69\x6c\x74\x65\x72\x00\x00\x0b\x00\x02\x00\x4f\x55\x54\x50\x55\x54\x00\x00\x0c\x00\x03\x00"...}, iov_len=16536}], msg_iovlen=1, msg_controllen=0, msg_flags=0}, 0) = 372
strace: Process 5748 detached

and this (output from atop):

  PID     TID   MINFLT   MAJFLT    VSTEXT   VSLIBS    VDATA    VSTACK    VSIZE    RSIZE    PSIZE     VGROW    RGROW   SWAPSZ    RUID       EUID        MEM   CMD        1/16
11575       -    61552        0      152K    2324K     5.0G      132K     5.1G     5.1G       0K    240.4M   240.5M       0K    root       root        33%   iptables

I had it growing till 10 GiB before I stopped it by SIGKILL to prevent
excessive swapping.

I will attach kernel configuration.

That is all I am willing to spend time on for now before going to sleep.
I will however reboot with older 4.20 kernel to see whether it is kernel
related.

[…]

-- System Information:
Debian Release: buster/sid
[…]
Kernel: Linux 5.0.0-rc2-tp520 (SMP w/4 CPU cores; PREEMPT)

Thanks,
-- 
Martin

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