[Bug 1903596] Re: stack trace in kernel

This bug is awaiting verification that the kernel in -proposed solves
the problem. Please test the kernel and update this bug with the
results. If the problem is solved, change the tag 'verification-needed-
bionic' to 'verification-done-bionic'. If the problem still exists,
change the tag 'verification-needed-bionic' to 'verification-failed-
bionic'.

If verification is not done by 5 working days from today, this fix will
be dropped from the source code, and this bug will be closed.

See https://wiki.ubuntu.com/Testing/EnableProposed for documentation how
to enable and use -proposed. Thank you!


** Tags added: verification-needed-bionic

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https://bugs.launchpad.net/bugs/1903596

Title:
stack trace in kernel

Status in linux package in Ubuntu:
Confirmed
Status in linux source package in Xenial:
Fix Committed
Status in linux source package in Bionic:
Fix Committed
Status in linux source package in Focal:
Fix Committed
Status in linux source package in Groovy:
Fix Committed
Status in linux source package in Hirsute:
Confirmed

Bug description:
== SRU Justification ==
Whenever a buggy NAPI driver returns more than its budget, it will
trigger a stack trace warning with:
WARN_ON_ONCE(work > weight);

The warning message looks like this :
WARNING: CPU: 2 PID: 0 at /build/linux-hwe-ymdo11/linux-hwe-4.15.0/net/core/dev.c:5672 net_rx_action+0x276/0x3b0

This is not very useful for debugging purpose, since it does not tell
you what's going on there.

== Fix ==
* 427d5838e996 ("net: napi: remove useless stack trace")

This patch will emit a message giving the function name, and a
descriptive message like:
NAPI poll function ath10k_pci_napi_poll+0x0/0x120 [ath10k_pci] returned 0, exceeding its budget of 64.

This patch is a clean-cherry for all the releases except Xenial.
For Xenial it will need to be applied with -C1

== Test ==
Test kernels can be found here:
https://people.canonical.com/~phlin/kernel/lp-1903596-napi-warnon/

Please note that even though I tried to reproduce this on a XPS 13
9360 mentioned in this bug report that shipped with Atheros QCA6174
[168c:003e] wireless card, but I can't trigger this warning message.
The bug opener is also unable to test this due to some other reasons.

Howeve I did tried to trigger this warning forcibly by putting it
outside the if statement with the test kernels in the following link
to make sure it won't cause some other problem.

https://people.canonical.com/~phlin/kernel/lp-1903596-napi-warnon
/force-to-warn/

== Where problems could occur ==
For this bug itself, this patch does not really solve the problem
but it will provide more debug information for developers in the
future (and since this is just a warning message, it should be fine).
We can expect to see more a detailed report against ath10k driver
in the future on launchpad.


== Original Bug Report ==
This appears to be a problem in the ath10k module. I am not sure what it is exactly.

ProblemType: Bug
DistroRelease: Ubuntu 16.04
Package: linux-image-4.15.0-122-generic 4.15.0-122.124~16.04.1
ProcVersionSignature: Ubuntu 4.15.0-122.124~16.04.1-generic 4.15.18
Uname: Linux 4.15.0-122-generic x86_64
ApportVersion: 2.20.1-0ubuntu2.26
Architecture: amd64
CurrentDesktop: Unity
Date: Mon Nov 9 13:35:54 2020
DistributionChannelDescriptor:
 # This is a distribution channel descriptor
 # For more information see http://wiki.ubuntu.com/DistributionChannelDescriptor
 canonical-oem-somerville-xenial-amd64-20160624-2
InstallationDate: Installed on 2020-11-09 (0 days ago)
InstallationMedia: Ubuntu 16.04 "Xenial" - Build amd64 LIVE Binary 20160624-10:47
SourcePackage: linux-signed-hwe
UpgradeStatus: No upgrade log present (probably fresh install)

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