Background

==========

The upstream Linux kernel maintainers only fix bugs for specific kernel

versions. Those versions include the current "release candidate" (or -rc)

kernel, any "stable" kernel versions, and any "long term" kernels.

Please see https://www.kernel.org/ for a list of supported kernels. Any

kernel marked with [EOL] is "end of life" and will not have any fixes

backported to it.

If you've found a bug on a kernel version isn't listed on kernel.org,

contact your Linux distribution or embedded vendor for support.

Alternatively, you can attempt to run one of the supported stable or -rc

kernels, and see if you can reproduce the bug on that. It's preferable

to reproduce the bug on the latest -rc kernel.

How to report Linux kernel bugs

===============================

Identify the problematic subsystem

----------------------------------

Identifying which part of the Linux kernel might be causing your issue

increases your chances of getting your bug fixed. Simply posting to the

generic linux-kernel mailing list (LKML) may cause your bug report to be

lost in the noise of a mailing list that gets 1000+ emails a day.

Instead, try to figure out which kernel subsystem is causing the issue,

and email that subsystem's maintainer and mailing list. If the subsystem

maintainer doesn't answer, then expand your scope to mailing lists like

LKML.

Identify who to notify

----------------------

Once you know the subsystem that is causing the issue, you should send a

bug report. Some maintainers prefer bugs to be reported via bugzilla

(https://bugzilla.kernel.org), while others prefer that bugs be reported

via the subsystem mailing list.

To find out where to send an emailed bug report, find your subsystem or

device driver in the MAINTAINERS file. Search in the file for relevant

entries, and send your bug report to the person(s) listed in the "M:"

lines, making sure to Cc the mailing list(s) in the "L:" lines. When the

maintainer replies to you, make sure to 'Reply-all' in order to keep the

public mailing list(s) in the email thread.

If you know which driver is causing issues, you can pass one of the driver

files to the get_maintainer.pl script:

perl scripts/get_maintainer.pl -f <filename>

If it is a security bug, please copy the Security Contact listed in the

MAINTAINERS file. They can help coordinate bugfix and disclosure. See

Documentation/SecurityBugs for more information.

If you can't figure out which subsystem caused the issue, you should file

a bug in kernel.org bugzilla and send email to

linux-kernel@vger.kernel.org, referencing the bugzilla URL. (For more

information on the linux-kernel mailing list see

http://www.tux.org/lkml/).

Tips for reporting bugs

-----------------------

If you haven't reported a bug before, please read:

http://www.chiark.greenend.org.uk/~sgtatham/bugs.html

http://www.catb.org/esr/faqs/smart-questions.html

It's REALLY important to report bugs that seem unrelated as separate email

threads or separate bugzilla entries. If you report several unrelated

bugs at once, it's difficult for maintainers to tease apart the relevant

data.

Gather information

------------------

The most important information in a bug report is how to reproduce the

bug. This includes system information, and (most importantly)

step-by-step instructions for how a user can trigger the bug.

If the failure includes an "OOPS:", take a picture of the screen, capture

a netconsole trace, or type the message from your screen into the bug

report. Please read "Documentation/oops-tracing.txt" before posting your

bug report. This explains what you should do with the "Oops" information

to make it useful to the recipient.

This is a suggested format for a bug report sent via email or bugzilla.

Having a standardized bug report form makes it easier for you not to

overlook things, and easier for the developers to find the pieces of

information they're really interested in. If some information is not

relevant to your bug, feel free to exclude it.

First run the ver_linux script included as scripts/ver_linux, which

reports the version of some important subsystems. Run this script with

the command "sh scripts/ver_linux".

Use that information to fill in all fields of the bug report form, and

post it to the mailing list with a subject of "PROBLEM: <one line

summary from [1.]>" for easy identification by the developers.

[1.] One line summary of the problem:

[2.] Full description of the problem/report:

[3.] Keywords (i.e., modules, networking, kernel):

[4.] Kernel information

[4.1.] Kernel version (from /proc/version):

[4.2.] Kernel .config file:

[5.] Most recent kernel version which did not have the bug:

[6.] Output of Oops.. message (if applicable) with symbolic information

resolved (see Documentation/oops-tracing.txt)

[7.] A small shell script or example program which triggers the

problem (if possible)

[8.] Environment

[8.1.] Software (add the output of the ver_linux script here)

[8.2.] Processor information (from /proc/cpuinfo):

[8.3.] Module information (from /proc/modules):

[8.4.] Loaded driver and hardware information (/proc/ioports, /proc/iomem)

[8.5.] PCI information ('lspci -vvv' as root)

[8.6.] SCSI information (from /proc/scsi/scsi)

[8.7.] Other information that might be relevant to the problem

(please look in /proc and include all information that you

think to be relevant):

[X.] Other notes, patches, fixes, workarounds:

Follow up

=========

Expectations for bug reporters

------------------------------

Linux kernel maintainers expect bug reporters to be able to follow up on

bug reports. That may include running new tests, applying patches,

recompiling your kernel, and/or re-triggering your bug. The most

frustrating thing for maintainers is for someone to report a bug, and then

never follow up on a request to try out a fix.

That said, it's still useful for a kernel maintainer to know a bug exists

on a supported kernel, even if you can't follow up with retests. Follow

up reports, such as replying to the email thread with "I tried the latest

kernel and I can't reproduce my bug anymore" are also helpful, because

maintainers have to assume silence means things are still broken.

Expectations for kernel maintainers

-----------------------------------

Linux kernel maintainers are busy, overworked human beings. Some times

they may not be able to address your bug in a day, a week, or two weeks.

If they don't answer your email, they may be on vacation, or at a Linux

conference. Check the conference schedule at LWN.net for more info:

https://lwn.net/Calendar/

In general, kernel maintainers take 1 to 5 business days to respond to

bugs. The majority of kernel maintainers are employed to work on the

kernel, and they may not work on the weekends. Maintainers are scattered

around the world, and they may not work in your time zone. Unless you

have a high priority bug, please wait at least a week after the first bug

report before sending the maintainer a reminder email.

The exceptions to this rule are regressions, kernel crashes, security holes,

or userspace breakage caused by new kernel behavior. Those bugs should be

addressed by the maintainers ASAP. If you suspect a maintainer is not

responding to these types of bugs in a timely manner (especially during a

merge window), escalate the bug to LKML and Linus Torvalds.

Thank you!

[Some of this is taken from Frohwalt Egerer's original linux-kernel FAQ]