linux-kernel - RE: [GIT PULL] gcc-plugin updates for v4.19-rc1

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Message-ID: <8d9dd1f35af1463dbeaf03c9d028020b@AcuMS.aculab.com>
Date:   Thu, 16 Aug 2018 09:51:41 +0000
From:   David Laight <David.Laight@...LAB.COM>
To:     'Linus Torvalds' <torvalds@...ux-foundation.org>,
        Kees Cook <keescook@...omium.org>
CC:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Alexander Popov <alex.popov@...ux.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Ingo Molnar" <mingo@...nel.org>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tycho Andersen <tycho@...ho.ws>,
        "Mark Rutland" <mark.rutland@....com>,
        Laura Abbott <labbott@...hat.com>,
        "Will Deacon" <will.deacon@....com>
Subject: RE: [GIT PULL] gcc-plugin updates for v4.19-rc1

From: Linus Torvalds
> Sent: 15 August 2018 21:19
...
> But if people run things on real machines, then BUG() is absolutely
> the last thing you EVER want to do for "debugging".

I'm not sure you want it on a live system either.
Live systems are where the 'hard' bugs show up.

I've just spent a couple of days pulling my hair out trying to work
out how to debug a customer system that was locking up solid when
running some new (and not completely testable by us) kernel code.

At 4am I suddenly realised that the distribution they are using
might be enabling 'panic_on_oops' by default.
Turning that off showed what was going wrong.

It wouldn't be as bad if Linux implemented 'dump to swap'.

For 'errors' that aren't completely fatal the system could
'fast shutdown' a lot of processes (maybe just refuse to schedule
them) while leaving enough running for fault diagnosis.
I'm not sure how you'd decide what to allow to run though.

	David

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