Messages in this thread | | | From | David Hildenbrand <> | Subject | [PATCH RFC 0/2] coding-style.rst: document BUG() and WARN() rules | Date | Wed, 24 Aug 2022 18:30:58 +0200 |
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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.
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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@linux-foundation.org> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Ingo Molnar <mingo@kernel.org> Cc: David Laight <David.Laight@ACULAB.COM> Cc: Jonathan Corbet <corbet@lwn.net> Cc: Andy Whitcroft <apw@canonical.com> Cc: Joe Perches <joe@perches.com> Cc: Dwaipayan Ray <dwaipayanray1@gmail.com> Cc: Lukas Bulwahn <lukas.bulwahn@gmail.com> Cc: Baoquan He <bhe@redhat.com> Cc: Vivek Goyal <vgoyal@redhat.com> Cc: Dave Young <dyoung@redhat.com>
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
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