[net-next,v2,0/5] netconsole: Add support for CPU population

Message

Breno Leitao Jan. 15, 2025, 1:35 p.m. UTC

The current implementation of netconsole sends all log messages in
parallel, which can lead to an intermixed and interleaved output on the
receiving side. This makes it challenging to demultiplex the messages
and attribute them to their originating CPUs.

As a result, users and developers often struggle to effectively analyze
and debug the parallel log output received through netconsole.

Example of a message got from produciton hosts:

	------------[ cut here ]------------
	------------[ cut here ]------------
	refcount_t: saturated; leaking memory.
	WARNING: CPU: 2 PID: 1613668 at lib/refcount.c:22 refcount_warn_saturate+0x5e/0xe0
	refcount_t: addition on 0; use-after-free.
	WARNING: CPU: 26 PID: 4139916 at lib/refcount.c:25 refcount_warn_saturate+0x7d/0xe0
	Modules linked in: bpf_preload(E) vhost_net(E) tun(E) vhost(E)

This series of patches introduces a new feature to the netconsole
subsystem that allows the automatic population of the CPU number in the
userdata field for each log message. This enhancement provides several
benefits:

* Improved demultiplexing of parallel log output: When multiple CPUs are
  sending messages concurrently, the added CPU number in the userdata
  makes it easier to differentiate and attribute the messages to their
  originating CPUs.

* Better visibility into message sources: The CPU number information
  gives users and developers more insight into which specific CPU a
  particular log message came from, which can be valuable for debugging
  and analysis.

The changes in this series are as follows:

Patch 1: netconsole: Rename userdata to extradata
=================================================
Create the a concept of extradata, which encompasses the concept of
userdata and the upcoming sysdatao

Sysdata is a new concept being added, which is basically fields that are
populated by the kernel. At this time only the CPU#, but, there is a
desire to add current task name, kernel release version, etc.

Patch 2: netconsole: Helper to count number of used entries
===========================================================
Create a simple helper to count number of entries in extradata. I am
separating this in a function since it will need to count userdata and
sysdata. For instance, when the user adds an extra userdata, we need to
check if there is space, counting the previous data entries (from
userdata and cpu data)

Patch 3: netconsole: add support for sysdata and CPU population
===============================================================
This is the core patch. Basically add a new option to enable automatic
CPU number population in the netconsole userdata Provides a new "cpu_nr"
sysfs attribute to control this feature

Patch 4: "netconsole: selftest: test CPU number auto-population"
=============================================================
Expands the existing netconsole selftest to verify the CPU number
auto-population functionality Ensures the received netconsole messages
contain the expected "cpu=<CPU>" entry in the message. Test different
permutation with userdata

Patch 5: "netconsole: docs: Add documentation for CPU number auto-population"
=============================================================================
Updates the netconsole documentation to explain the new CPU number
auto-population feature Provides instructions on how to enable and use
the feature

I believe these changes will be a valuable addition to the netconsole
subsystem, enhancing its usefulness for kernel developers and users.

Signed-off-by: Breno Leitao <[e-mail]>
---
Changes in v2:
- Create the concept of extradata and sysdata. This will make the design
  easier to understand, and the code easier to read.
  * Basically extradata encompasses userdata and the new sysdata.
    Userdata originates from user, and sysdata originates in kernel.
- Improved the test to send from a very specific CPU, which can be
  checked to be correct on the other side, as suggested by Jakub.
- Fixed a bug where CPU # was populated at the wrong place
- Link to v1: https://lore.kernel.org/r/[e-mail]

---
Breno Leitao (5):
      netconsole: Rename userdata to extradata
      netconsole: Helper to count number of used entries
      netconsole: add support for sysdata and CPU population
      netconsole: selftest: test for sysdata CPU
      netconsole: docs: Add documentation for CPU number auto-population

 Documentation/networking/netconsole.rst            |  45 +++++
 drivers/net/netconsole.c                           | 223 ++++++++++++++++-----
 tools/testing/selftests/drivers/net/Makefile       |   1 +
 .../selftests/drivers/net/lib/sh/lib_netcons.sh    |  17 ++
 .../selftests/drivers/net/netcons_sysdata.sh       | 166 +++++++++++++++
 5 files changed, 407 insertions(+), 45 deletions(-)
---
base-commit: 7b24f164cf005b9649138ef6de94aaac49c9f3d1
change-id: 20241108-netcon_cpu-ce3917e88f4b

Best regards,