linux-kernel - Re: [PATCH] mm/mmap: replace if (cond) BUG() with BUG

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Date:   Wed, 6 Jan 2021 15:09:30 -0500
From:   Andrea Arcangeli <aarcange@...hat.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Hugh Dickins <hughd@...gle.com>,
        Alex Shi <alex.shi@...ux.alibaba.com>,
        Minchan Kim <minchan@...nel.org>,
        Michal Hocko <mhocko@...e.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mm/mmap: replace if (cond) BUG() with BUG_ON()

Hello,

On Wed, Jan 06, 2021 at 11:46:20AM -0800, Andrew Morton wrote:
> On Tue, 5 Jan 2021 20:28:27 -0800 (PST) Hugh Dickins <hughd@...gle.com> wrote:
> 
> > Alex, please consider why the authors of these lines (whom you
> > did not Cc) chose to write them without BUG_ON(): it has always
> > been preferred practice to use BUG_ON() on predicates, but not on
> > functionally effective statements (sorry, I've forgotten the proper
> > term: I'd say statements with side-effects, but here they are not
> > just side-effects: they are their main purpose).
> > 
> > We prefer not to hide those away inside BUG macros
> 
> Should we change that?  I find BUG_ON(something_which_shouldnt_fail())
> to be quite natural and readable.
> 
> As are things like the existing
> 
> BUG_ON(mmap_read_trylock(mm));
> BUG_ON(wb_domain_init(&global_wb_domain, GFP_KERNEL));
> 
> etc.
> 
> 
> No strong opinion here, but is current mostly-practice really
> useful?

I'd be surprised if the kernel can boot with BUG_ON() defined as "do
{}while(0)" so I guess it doesn't make any difference.

I've no strong opinion either, but personally my views matches Hugh's
views on this. I certainly tried to stick to that in the past since I
find it cleaner if a bugcheck just "checks" and can be deleted at any
time without sudden breakage.

Said that I also guess we're in the minority.

Thanks,
Andrea