Add goals of patch review and tips

I see two options for patch review. Either we have a single senior
maintainer who does most of or it is distributed.

For now I think it needs to be distributed which is beyond the scope
of this commit.

In order to distribute it we need new contributors to review each
others' work at least for the first few revisions.

I think that anyone can review a patch if they put the work in to test
it and try to break it. Then understand why it is broken.

This commit states some ideas about how to do that, plus some tips for
more advanced patch review.

Signed-off-by: Richard Palethorpe <rpalethorpe@suse.com>
Reviewed-by: Avinesh Kumar <akumar@suse.de>
Reviewed-by: Cyril Hrubis <chrubis@suse.cz>

Cc: Petr Vorel <pvorel@suse.cz>
Cc: iob <ybonatakis@suse.com>
Cc: Li Wang <liwang@redhat.com>

doc/maintainer-patch-review-checklist.txt

@@ -1,4 +1,86 @@
-# Maintainer Patch Review Checklist
+# Patch Review
+
+Anyone can and should review patches. It's the only way to get good at
+patch review and for the project to scale.
+
+## Goals of patch review
+
+1. Prevent false positive test results
+2. Prevent false negative test results
+3. Keep the code as simple as possible, but no simpler
+
+## How to find clear errors
+
+A clear error is one where there is unlikely to be any argument if you
+provide evidence of it. Evidence being an error trace or logical proof
+that an error will occur in a common situation.
+
+The following are examples and may not be appropriate for all tests.
+
+* Merge the patch locally. It should apply cleanly to master.
+* Compile the patch with default and non-default configurations.
+  - Use sanitizers e.g. undefined behaviour, address.
+  - Compile on non-x86
+  - Compile on x86 with -m32
+* Use `make check`
+* Run effected tests in a VM
+  - Use single vCPU
+  - Use many vCPUs and enable NUMA
+  - Restrict RAM to < 1GB.
+* Run effected tests on an embedded device
+* Run effected tests on non-x86 machine in general
+* Run reproducers on a kernel where the bug is present
+* Run tests with "-i0"
+* Compare usage of system calls with man page descriptions
+* Compare usage of system calls with kernel code
+* Search the LTP library for existing helper functions
+
+## How to find subtle errors
+
+A subtle error is one where you can expect some argument because you
+do not have clear evidence of an error. It is best to state these as
+questions and not make assertions if possible.
+
+Although if it is a matter of style or "taste" then senior maintainers
+can assert what is correct to avoid bike shedding.
+
+* Ask what happens if there is an error, could it be debugged just
+  with the test output?
+* Are we testing undefined behavior?
+  - Could future kernel behaviour change without "breaking userland"?
+  - Does the kernel behave differently depending on hardware?
+  - Does it behave differently depending on kernel configuration?
+  - Does it behave differently depending on the compiler?
+  - Would it behave differently if the order of checks on syscall parameters
+    changed in the kernel?
+* Will it scale to tiny and huge systems?
+  - What happens if there are 100+ CPUs?
+  - What happens if each CPU core is very slow?
+  - What happens if there are 2TB of RAM?
+* Are we repeating a pattern that can be turned into a library function?
+* Is a single test trying to do too much?
+* Could multiple similar tests be merged?
+* Race conditions
+  - What happens if a process gets preempted?
+  - Could checkpoints or fuzzsync by used instead?
+  - Note, usually you can insert a sleep to prove a race condition
+    exists however finding them is hard
+* Is there a simpler way to achieve the same kernel coverage?
+
+## How to get patches merged
+
+Once you think a patch is good enough you should add your Reviewed-by
+and/or Tested-by tags. This means you will get some credit for getting
+the patch merged. Also some blame if there are problems.
+
+If you ran the test you can add the Tested-by tag. If you read the
+code or used static analysis tools on it, you can add the Reviewed-by
+tag.
+
+In addition you can expect others to review your patches and add their
+tags. This will speed up the process of getting your patches merged.
+
+## Maintainers Checklist
 
 Patchset should be tested locally and ideally also in maintainer's fork in
 GitHub Actions on GitHub.