[Dnsmasq-discuss] dnsmasq using 100% of cpu
Simon Kelley
simon at thekelleys.org.uk
Mon Feb 17 20:32:49 GMT 2020
On 17/02/2020 13:31, Donald Sharp wrote:
> Running:
>
> sharpd at eva:~/dnsmasq$ /sbin/dnsmasq --version
> Dnsmasq version 2.80 Copyright (c) 2000-2018 Simon Kelley
> Compile time options: IPv6 GNU-getopt DBus i18n IDN DHCP DHCPv6 no-Lua
> TFTP conntrack ipset auth DNSSEC loop-detect inotify dumpfile
> ----
>
> When I install several hundred thousand routes into the kernel and
> remove them( or some variation thereof ), dnsmasq eventually ends up
> running 100% cpu:
>
> top - 18:45:18 up 1 day, 7:44, 1 user, load average: 2.70, 2.65, 2.34
> Tasks: 424 total, 3 running, 421 sleeping, 0 stopped, 0 zombie
> %Cpu(s): 12.1 us, 6.9 sy, 0.0 ni, 80.2 id, 0.0 wa, 0.0 hi, 0.7 si,
> 0.0 st
> MiB Mem : 32131.3 total, 19483.6 free, 6620.3 used, 6027.4 buff/cache
> MiB Swap: 32718.0 total, 31693.0 free, 1025.0 used. 24698.2 avail Mem
>
> PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+
> COMMAND
> 293183 nobody 20 0 11040 2040 1688 R 99.7 0.0 148:48.40
> dnsmasq
>
> strace output:
>
> poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=5,
> events=POLLIN}, {fd=6, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8,
> events=POLLIN}], 6, -1) = 1 ([{fd=4, revents=POLLERR}])
> poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=5,
> events=POLLIN}, {fd=6, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8,
> events=POLLIN}], 6, -1) = 1 ([{fd=4, revents=POLLERR}])
> poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=5,
> events=POLLIN}, {fd=6, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8,
> events=POLLIN}], 6, -1) = 1 ([{fd=4, revents=POLLERR}])
> poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=5,
> events=POLLIN}, {fd=6, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8,
> events=POLLIN}], 6, -1) = 1 ([{fd=4, revents=POLLERR}])
> poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=5,
> events=POLLIN}, {fd=6, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8,
> events=POLLIN}], 6, -1) = 1 ([{fd=4, revents=POLLERR}])
> poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=5,
> events=POLLIN}, {fd=6, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8,
> events=POLLIN}], 6, -1) = 1 ([{fd=4, revents=POLLERR}])
> poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=5,
> events=POLLIN}, {fd=6, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8,
> events=POLLIN}], 6, -1) = 1 ([{fd=4, revents=POLLERR}])
> poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=5,
> events=POLLIN}, {fd=6, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8,
> events=POLLIN}], 6, -1) = 1 ([{fd=4, revents=POLLERR}])
> poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=5,
> events=POLLIN}, {fd=6, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8,
> events=POLLIN}], 6, -1) = 1 ([{fd=4, revents=POLLERR}])
> poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=5,
> events=POLLIN}, {fd=6, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8,
> events=POLLIN}], 6, -1) = 1 ([{fd=4, revents=POLLERR}])
> poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=5,
> events=POLLIN}, {fd=6, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8,
> events=POLLIN}], 6, -1) = 1 ([{fd=4, revents=POLLERR}])
> poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=5,
> events=POLLIN}, {fd=6, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8,
> events=POLLIN}], 6, -1) = 1 ([{fd=4, revents=POLLERR}])
> poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=5,
> events=POLLIN}, {fd=6, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8,
> events=POLLIN}], 6, -1) = 1 ([{fd=4, revents=POLLERR}])
> poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=5,
> events=POLLIN}, {fd=6, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8,
> events=POLLIN}], 6, -1) = 1 ([{fd=4, revents=POLLERR}])
> poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=5,
> events=POLLIN}, {fd=6, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8,
> events=POLLIN}], 6, -1) = 1 ([{fd=4, revents=POLLERR}])
> poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=5,
> events=POLLIN}, {fd=6, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8,
> events=POLLIN}], 6, -1) = 1 ([{fd=4, revents=POLLERR}])
> poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=5,
> events=POLLIN}, {fd=6, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8,
> events=POLLIN}], 6, -1) = 1 ([{fd=4, revents=POLLERR}])
> poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=5,
> events=POLLIN}, {fd=6, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8,
> events=POLLIN}], 6, -1) = 1 ([{fd=4, revents=POLLERR}])
> poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=5,
> events=POLLIN}, {fd=6, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8,
> events=POLLIN}], 6, -1) = 1 ([{fd=4, revents=POLLERR}])
> poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=5,
> events=POLLIN}, {fd=6, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8,
> events=POLLIN}], 6, -1) = 1 ([{fd=4, revents=POLLERR}])
> poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=5,
> events=POLLIN}, {fd=6, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8,
> events=POLLIN}], 6, -1) = 1 ([{fd=4, revents=POLLERR}])
> poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=5,
> events=POLLIN}, {fd=6, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8,
> events=POLLIN}], 6, -1) = 1 ([{fd=4, revents=POLLERR}])
> poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=5,
> events=POLLIN}, {fd=6, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8,
> events=POLLIN}], 6, -1) = 1 ([{fd=4, revents=POLLERR}])
> poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=5,
> events=POLLIN}, {fd=6, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8,
> events=POLLIN}], 6, -1) = 1 ([{fd=4, revents=POLLERR}])
> poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=5,
> events=POLLIN}, {fd=6, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8,
> events=POLLIN}], 6, -1) = 1 ([{fd=4, revents=POLLERR}])
> poll([{fd=3, events=POLLIN}, {fd=4, events=POLLIN}, {fd=5,
> events=POLLIN}, {fd=6, events=POLLIN}, {fd=7, events=POLLIN}, {fd=8,
> events=POLLIN}], 6, -1) = 1 ([{fd=4, revents=PO^Cstrace: Process 293183
> detached
>
> I can pretty much make this happen at will. What can I provide to help
> debug this?
The first thing I'd like to know is what file descriptor 4 is, providing
us with the first (say) 500 or 1000 lines of strace output would help
with that.
>
> As a side note, I was not placing these routes into the default linux
> routing table. Does dnsmasq need to be paying attention to these routes?
>
To save typing I've just pasted a comment from the code which explains
why adding routes affects dnsmasq
/* We arrange to receive netlink multicast messages whenever the
network route is added.
If this happens and we still have a DNS packet in the buffer,
we re-send it.
This helps on DoD links, where frequently the packet which
triggers dialling is
a DNS query, which then gets lost. By re-sending, we can avoid
the lookup
failing. */
I suspect that the solution to this is to restrict the above to the
"main" routing table.
Simon.
> donald
>
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