netconsole hands every console message to every enabled target, with no
bound on the rate.
At Meta, a few hosts caused some DoS and netconsd was OOM killed in
some regions, fed by 3 billion RCU messages from thousand hosts and by
a swap fault that retries forever, which logged 6 million copies of one
line on a single host in a few hours.
Both floods are being fixed where they are printed, by Paula and me for RCU
Tasks [1][2][3] and by me for swap faul fix [4], but that only ever
covers the flood already found, not new issues that might be happening.
Use the ratelimit in the kernel to ratelimit messages from netconsole.
Give each target a token bucket, consulted once per message so that a
message split into several ncfrag packets is sent whole or dropped
whole.
It starts with a zero interval, which struct ratelimit_state treats as
unlimited, so nothing changes until ratelimit_interval_ms and
ratelimit_burst are written.
What the bucket discards is reported on the wire, so the receiver sees
"netconsole: 45 messages dropped by rate limit" rather than an
unexplained gap. This is what is captured on netconsd, when this patch
is applied:
7.2.0-rc7-01460-g75848acaf136,13,628,252392647,-;netconsole selftest:
netcons_AGujw 1
7.2.0-rc7-01460-g75848acaf136,13,629,252392782,-;netconsole selftest:
netcons_AGujw 2
....
7.2.0-rc7-01460-g75848acaf136,4,0,254742176,-;netconsole: 45 messages
dropped by rate limit
7.2.0-rc7-01460-g75848acaf136,13,678,254742125,-;netconsole selftest:
netcons_AGujw 1
Crash output is exempt. The bucket is skipped while oops_in_progress is
set, so a limit configured for steady-state logging cannot cost a target
part of an oops or a panic.
[1] https://lore.kernel.org/all/[email protected]/
[2]
https://lore.kernel.org/all/[email protected]/
[3]
https://lore.kernel.org/all/[email protected]/
[4] https://lore.kernel.org/all/[email protected]/
Signed-off-by: Breno Leitao <[email protected]>
---
Breno Leitao (6):
netconsole: add a per-target message rate limit
netconsole: allow configuring the rate limit interval through configfs
netconsole: allow configuring the rate limit burst through configfs
netconsole: tell the target when the rate limit drops messages
docs: netconsole: document rate limit feature
selftests: netcons: test the per-target rate limit
Documentation/networking/netconsole.rst | 43 ++++++
drivers/net/netconsole.c | 145 +++++++++++++++++++
.../selftests/drivers/net/netconsole/Makefile | 1 +
.../drivers/net/netconsole/netcons_ratelimit.sh | 160 +++++++++++++++++++++
4 files changed, 349 insertions(+)
---
base-commit: e6a5d573d24cd375e09d24f136523cb3cc85c9d3
change-id: 20260817-netcons_ratelimit-629b04a73c57
Best regards,
--
Breno Leitao <[email protected]>
