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Thu, 7 Jan 2021 17:36:05 +0000 (UTC) Received: from mail (ovpn-112-222.rdu2.redhat.com [10.10.112.222]) by smtp.corp.redhat.com (Postfix) with ESMTPS id DDEC860C0F; Thu, 7 Jan 2021 17:36:04 +0000 (UTC) Date: Thu, 7 Jan 2021 12:36:04 -0500 From: Andrea Arcangeli To: Vlastimil Babka Cc: Hugh Dickins , Andrew Morton , Alex Shi , Minchan Kim , Michal Hocko , linux-mm@kvack.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH] mm/mmap: replace if (cond) BUG() with BUG_ON() Message-ID: References: <1607743586-80303-1-git-send-email-alex.shi@linux.alibaba.com> <1607743586-80303-2-git-send-email-alex.shi@linux.alibaba.com> <20210106114620.5c221690f3a9cad7afcc3077@linux-foundation.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/2.0.4 (2020-12-30) X-Scanned-By: MIMEDefang 2.79 on 10.5.11.12 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Thu, Jan 07, 2021 at 06:28:29PM +0100, Vlastimil Babka wrote: > On 1/6/21 9:18 PM, Hugh Dickins wrote: > > On Wed, 6 Jan 2021, Andrea Arcangeli wrote: > >> > >> 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 had been afraid of that too, when CONFIG_BUG is not set: > > but I think it's actually "if (cond) do {} while (0)". > > It's a maze of configs and arch-specific vs generic headers, but I do see this > in include/asm-generic/bug.h: > > #else /* !CONFIG_BUG */ > #ifndef HAVE_ARCH_BUG > #define BUG() do {} while (1) > #endif > > So seems to me there *are* configurations possible where side-effects are indeed > thrown away, right? But this not BUG_ON, and that is an infinite loop while(1), not an optimization away as in while (0) that I was suggesting to just throw away cond and make it a noop. BUG() is actually the thing to use to move functional stuff out of BUG_ON so it's not going to be causing issues if it just loops. This overall feels mostly an aesthetically issue. Thanks, Andrea