Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
MIME-Version: 1.0
References: <20221031175256.2813280-1-jannh@google.com> <Y2APCmYNjYOYLf8G@ZenIV>
In-Reply-To: <Y2APCmYNjYOYLf8G@ZenIV>
From:   Jann Horn <jannh@google.com>
Date:   Mon, 31 Oct 2022 19:13:30 +0100
Message-ID: <CAG48ez094n05c3QJMy7vZ5U=z87MzqYeKU97Na_R9O36_LJSXw@mail.gmail.com>
Subject: Re: [PATCH v2] fs: use acquire ordering in __fget_light()
To:     Al Viro <viro@zeniv.linux.org.uk>
Cc:     Linus Torvalds <torvalds@linux-foundation.org>,
        Miklos Szeredi <mszeredi@redhat.com>,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        Will Deacon <will@kernel.org>
Content-Type: text/plain; charset="UTF-8"
Precedence: bulk

On Mon, Oct 31, 2022 at 7:08 PM Al Viro <viro@zeniv.linux.org.uk> wrote:
[...]
> No arch-specific instances, so...
> static __always_inline int
> arch_atomic_read_acquire(const atomic_t *v)
> {
>         int ret;
>
>         if (__native_word(atomic_t)) {
>                 ret = smp_load_acquire(&(v)->counter);
>         } else {
>                 ret = arch_atomic_read(v);
>                 __atomic_acquire_fence();
>         }
>
>         return ret;
> }
[...]
> Do we really have any architectures where a structure with one
> int field does *not* have a size that would satisfy that check?
>
> Is it future-proofing for masturbation sake, or am I missing something
> real here?

include/linux/atomic/atomic-arch-fallback.h has a comment at the top that says:

// Generated by scripts/atomic/gen-atomic-fallback.sh
// DO NOT MODIFY THIS FILE DIRECTLY