linux-kernel - Re: BUG_ON() in workingset_node_shadows

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Message-ID: <CA+55aFy6a8BVWtqgeJKZuhU-CZFVZ3X90SdQ5z+NTDDsEOnpJA@mail.gmail.com>
Date:   Mon, 3 Oct 2016 21:12:48 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Johannes Weiner <hannes@...xchg.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 Mon, Oct 3, 2016 at 9:07 PM, Andrew Morton <akpm@...ux-foundation.org> wrote:
>
> Well, it's a VM_BUG_ON and few people run with CONFIG_DEBUG_VM.

Ehh. If by "few people" you mean "pretty much everybody", you'd be
right, but your choice of wording would be somewhat misleading,
wouldn't you say?

Hint: here's a line from the standard Fedora kernel config:

    CONFIG_DEBUG_VM=y

so *no*. VM_BUG_ON() is no less deadly than a regular BUG_ON(). It
just allows some people to build smaller kernels, but apparently
distro people would rather have debugging than save a few kB of RAM.

The VM debvugging code has VM_WARN_ON() and VM_WARN_ON_ONCE() for
people who want to get a "oops, my assumptions were wrong"

Killing machines because somebody made an assumption that was wrong is not ok.

Killing the machine is ok if we have a situation where there literally
is no other choice.

                  Linus