From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 302C7C32772 for ; Wed, 17 Aug 2022 21:04:15 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S242088AbiHQVEN (ORCPT ); Wed, 17 Aug 2022 17:04:13 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59566 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S242153AbiHQVEI (ORCPT ); Wed, 17 Aug 2022 17:04:08 -0400 Received: from mail-qv1-f43.google.com (mail-qv1-f43.google.com [209.85.219.43]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id DF03CA1D49; Wed, 17 Aug 2022 14:04:06 -0700 (PDT) Received: by mail-qv1-f43.google.com with SMTP id mn10so6230501qvb.10; Wed, 17 Aug 2022 14:04:06 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20210112; h=user-agent:in-reply-to:content-disposition:mime-version:references :message-id:subject:cc:to:from:date:x-gm-message-state:from:to:cc; bh=kIlfxyqwO0rTrcxkh/EF7Gqy6pDlNX5yvWxQZRLIpHY=; b=D3QtODsgxGj1hya3LiYDo4K7AOe2pGQkCToZyqxVkMdCOaLhqWu1Q6jU7mBaChWro0 MZOoieCovzQylv32d5H5DIo4jmPW6pWaK5F+yqY4OU24bvfUyOjw4hROGnmtLXaIeEau JjoJp8Ig7YggpNdQ3hAI4PMt3v/Ce8fARg+trtVEDT1NNwhPD49bEA8kq+wVtA7dxqw7 rJTBAaMG/QQh6fPKUSoQYyIY1KrnBpfKxNyTpm9riXEGz4ksR+q9vkU9qPoYXlibQvUS CqlxWAdOOnnxYFoc1jfLCbMeLf2b+7kQjEh6FrIzi7o10PQiW/cCh0rc1sgEpR0Ak7do QCkw== X-Gm-Message-State: ACgBeo1mdq9OVqURgOr34Fh61fPtbHgl9DLFnDg3IYdZnqBPMkUhP9LT X2rZVQO9PMsbQ/e3z4U0UpM= X-Google-Smtp-Source: AA6agR6u5IP4+/+d/wECWVR6UmupsqqVAWFJ3gJEE5YMYiPTUeEczIZNL5Vv8cNtIYePsPAQeNUZQQ== X-Received: by 2002:a0c:8084:0:b0:472:f26b:59f7 with SMTP id 4-20020a0c8084000000b00472f26b59f7mr24203490qvb.62.1660770245874; Wed, 17 Aug 2022 14:04:05 -0700 (PDT) Received: from maniforge.dhcp.thefacebook.com ([2620:10d:c091:480::a5ed]) by smtp.gmail.com with ESMTPSA id fp25-20020a05622a509900b0034454aff529sm9611345qtb.80.2022.08.17.14.04.04 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 17 Aug 2022 14:04:05 -0700 (PDT) Date: Wed, 17 Aug 2022 16:03:28 -0500 From: David Vernet To: Andrii Nakryiko Cc: bpf@vger.kernel.org, ast@kernel.org, daniel@iogearbox.net, andrii@kernel.org, john.fastabend@gmail.com, martin.lau@linux.dev, song@kernel.org, yhs@fb.com, kpsingh@kernel.org, sdf@google.com, haoluo@google.com, jolsa@kernel.org, tj@kernel.org, joannelkoong@gmail.com, linux-kernel@vger.kernel.org, Kernel-team@fb.com Subject: Re: [PATCH 3/5] bpf: Add bpf_user_ringbuf_drain() helper Message-ID: References: <20220808155341.2479054-1-void@manifault.com> <20220808155341.2479054-3-void@manifault.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/2.2.7 (2022-08-07) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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().