linux-kernel - Re: semantics of rhashtable and sysvipc

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Date:   Wed, 23 May 2018 11:52:13 -0700
From:   Davidlohr Bueso <dave@...olabs.net>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Thomas Graf <tgraf@...g.ch>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Manfred Spraul <manfred@...orfullife.com>,
        guillaume.knispel@...ersonicimagine.com,
        Linux API <linux-api@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: semantics of rhashtable and sysvipc

On Wed, 23 May 2018, Linus Torvalds wrote:

>On Wed, May 23, 2018 at 11:47 AM Davidlohr Bueso <dave@...olabs.net> wrote:
>
>> Note that even if the allocation was guaranteed, there are still param
>validations
>> and rhashtable_init() can return -EINVAL.
>
>So?
>
>It's not going to happen, because you're not going to give garbage
>parameters.

Maybe EINVAL could be replaced with WARN_ON(). That would grab the programmer's
attention.

>
>Why would you add a BUG_ON() for something that cannot happen? You might as
>well sprinkle them randomly in every damn place.

Not suggesting this. Before I started the thread, I was actually thinking of
ipc using ENOMEM only for rhashtable_init() filure considering the EINVAL case
will never happen.

>
>And even if somebody screws up the parameters because they are being
>stupid, then SO WHAT? rhashtable_init() won't initialize the pointers, and
>we'll get a NULL pointer dereference.
>
>And hey, we'll probably get it later during boot, once the system is
>actually up and running, and that NULL pointer dereference might even get
>logged in the system logs now because the machine booted successfully, and
>mnaybe it will even get sent to a distro and debugged.
>
>So at what point was there _any_ advantage in doing a BUG_ON() for a crazy
>case?

For the record, I'm not arguing in favor of BUG_ON().