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Date:   Wed, 17 Aug 2022 16:03:28 -0500
From:   David Vernet <void@manifault.com>
To:     Andrii Nakryiko <andrii.nakryiko@gmail.com>
Cc:     bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net,
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Subject: Re: [PATCH 3/5] bpf: Add bpf_user_ringbuf_drain() helper
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On Wed, Aug 17, 2022 at 03:24:40PM -0500, David Vernet wrote:

> [...]
> > right, I think __atomic_store_n() can be used in libbpf for this with
> > seq_cst ordering
> 
> __atomic_store_n(__ATOMIC_SEQ_CST) will do the correct thing on x86, but it
> is not guaranteed to provide a full acq/rel barrier according to the C
> standard. __atomic_store_n(__ATOMIC_SEQ_CST) means "store-release, and also
> participates in the sequentially-consistent global ordering".
> 
> I believe we actually need an __atomic_store_n(__ATOMIC_ACQ_REL) here. I

Sorry, I meant __atomic_exchange_n() rather than __atomic_store_n().