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From:   Linus Torvalds <torvalds@linux-foundation.org>
Date:   Fri, 2 Jun 2023 16:07:10 -0400
Message-ID: <CAHk-=whKyWvzg=7_m1o_KLC3zb9FjTBHftc36-5M9X78AxwRXg@mail.gmail.com>
Subject: Re: [PATCH 3/3] fork, vhost: Use CLONE_THREAD to fix freezer/ps regression
To:     Oleg Nesterov <oleg@redhat.com>
Cc:     Jason Wang <jasowang@redhat.com>,
        Mike Christie <michael.christie@oracle.com>,
        linux@leemhuis.info, nicolas.dichtel@6wind.com, axboe@kernel.dk,
        ebiederm@xmission.com, linux-kernel@vger.kernel.org,
        virtualization@lists.linux-foundation.org, mst@redhat.com,
        sgarzare@redhat.com, stefanha@redhat.com, brauner@kernel.org
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On Fri, Jun 2, 2023 at 1:59=E2=80=AFPM Oleg Nesterov <oleg@redhat.com> wrot=
e:
>
> As I said from the very beginning, this code is fine on x86 because
> atomic ops are fully serialised on x86.

Yes. Other architectures require __smp_mb__{before,after}_atomic for
the bit setting ops to actually be memory barriers.

We *should* probably have acquire/release versions of the bit test/set
helpers, but we don't, so they end up being full memory barriers with
those things. Which isn't optimal, but I doubt it matters on most
architectures.

So maybe we'll some day have a "test_bit_acquire()" and a
"set_bit_release()" etc.

            Linus