linux-kernel - Re: BUG_ON() in workingset_node_shadows

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Message-ID: <20161007054824.GA9917@1wt.eu>
Date:   Fri, 7 Oct 2016 07:48:24 +0200
From:   Willy Tarreau <w@....eu>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Kees Cook <keescook@...omium.org>,
        Paul Gortmaker <paul.gortmaker@...driver.com>,
        Johannes Weiner <hannes@...xchg.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Antonio SJ Musumeci <trapexit@...wn.link>,
        Miklos Szeredi <miklos@...redi.hu>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        stable <stable@...r.kernel.org>
Subject: Re: BUG_ON() in workingset_node_shadows_dec() triggers

On Thu, Oct 06, 2016 at 04:59:20PM -0700, Linus Torvalds wrote:
> We should just switch BUG() over and be done with it. The whole point
> it that since it should never trigger in the first place, the
> semantics on BUG() should never matter.
> 
> And if you have some code that depends on the semantics of BUG(), that
> code is buggy crap *by*definition*.

I totally agree with this. If a developer writes BUG() somewhere, it
means he doesn't see how it is possible to end up in this situation.
Thus we cannot hope that the BUG() call is doing anything right to
fix what the code author didn't expect to happen. It just means
"try to limit the risks but I don't really know which ones".

Also we won't make things worse. Where people currently have an oops,
they'll get one or more warnings. The side effects (lockups, panic,
etc) will more or less be the same, but many of us already don't want
to continue after an oops and despite this our systems work fine, so
I don't see why anyone would suffer from such a change. However some
developers may get more details about issues than what they could get
in the past.

Willy