As it seems to be rather unclear if/when to use BUG(), BUG_ON(),
VM_BUG_ON(), WARN_ON_ONCE(), ... let's try to document the result of a
recent discussion.
Details can be found in patch #1.
--------------------------------------------------------------------------
Here is some braindump after thinking about BUG_ON(), WARN_ON(), ... and
how it interacts with kdump.
I was wondering what the expectation on a system with armed kdump are,
for example, after we removed most BUG_ON() instances and replaced them
by WARN_ON_ONCE(). I would assume that we actually want to panic in some
cases to capture a proper system dump instead of continuing and eventually
ending up with a completely broken system where it's hard to extract any
useful debug information. We'd have to enable panic_on_warn. But we'd only
want to do that in case kdump is actually armed after boot.
So one idea would be to have some kind of "panic_on_warn_with_kdump" mode.
But then, we'd actually crash+kdump even on the most harmless WARN_ON()
conditions, because they all look alike. To compensate, we would need
some kind of "severity" levels of a warning -- at least some kind of
"this is harmless and we can easily recover, but please tell the
developers" vs. "this is real bad and unexpected, capture a dump
immediately instead of trying to recover and eventually failing miserably".
But then, maybe we really want something like BUG_ON() -- let's call it
CBUG_ON() for simplicity -- but be able to make it be usable in
conditionals (to implement recovery code if easily possible) and make the
runtime behavior configurable.
if (CBUG_ON(whatever))
try_to_recover()
Whereby, for example, "panic_on_cbug" and "panic_on_cbug_with_kdump"
could control the runtime behavior.
But this is just a braindump and I assume people reading along have other,
better ideas. Especially, a better name for CBUG.
Cc: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: David Laight <David.Laight@xxxxxxxxxx>
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Andy Whitcroft <apw@xxxxxxxxxxxxx>
Cc: Joe Perches <joe@xxxxxxxxxxx>
Cc: Dwaipayan Ray <dwaipayanray1@xxxxxxxxx>
Cc: Lukas Bulwahn <lukas.bulwahn@xxxxxxxxx>
Cc: Baoquan He <bhe@xxxxxxxxxx>
Cc: Vivek Goyal <vgoyal@xxxxxxxxxx>
Cc: Dave Young <dyoung@xxxxxxxxxx>
David Hildenbrand (2):
coding-style.rst: document BUG() and WARN() rules ("do not crash the
kernel")
checkpatch: warn on usage of VM_BUG_ON() and friends
Documentation/process/coding-style.rst | 27 ++++++++++++++++++++++++++
scripts/checkpatch.pl | 6 +++---
2 files changed, 30 insertions(+), 3 deletions(-)
--
2.37.1
