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From:   Arnd Bergmann <arnd@kernel.org>
Date:   Tue, 5 Jan 2021 11:28:40 +0100
Message-ID: <CAK8P3a1E3zWHSkNOaKY80ZfZqVuEe11dr_Rop=eDkbmmHo1Z6A@mail.gmail.com>
Subject: Re: [PATCH] mm/mremap: fix BUILD_BUG_ON() error in get_extent
To:     Nathan Chancellor <natechancellor@gmail.com>
Cc:     Andrew Morton <akpm@linux-foundation.org>,
        Nick Desaulniers <ndesaulniers@google.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        Wei Yang <richard.weiyang@linux.alibaba.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Vlastimil Babka <vbabka@suse.cz>,
        Dmitry Safonov <0x7f454c46@gmail.com>,
        Brian Geffon <bgeffon@google.com>,
        Linux-MM <linux-mm@kvack.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        clang-built-linux <clang-built-linux@googlegroups.com>
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On Mon, Jan 4, 2021 at 11:36 PM Nathan Chancellor
<natechancellor@gmail.com> wrote:
>
> I am in agreement with Vlastimil, I would rather see the BUILD_BUG()
> dropped or converted into BUG() instead of papering over with
> __always_inline.

I see your point, but I also generally prefer build-time checks over
runtime ones wherever possible, and would prefer a way to keep
it in a form that allows that, at least if the check is considered useful
at all.

> For what it's worth, I only see this build failure
> with CONFIG_UBSAN_UNSIGNED_OVERFLOW, which you proposed disabling:
>
> https://lore.kernel.org/lkml/20201230154749.746641-1-arnd@kernel.org/

I'm building more randconfig kernels without this patch but with the
__always_inline
reverted now, will see if it comes back. If not, let's just drop this patch.

      Arnd