From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mail-wm1-f67.google.com (mail-wm1-f67.google.com [209.85.128.67]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id B87F0258EE9 for ; Mon, 26 Jan 2026 18:29:31 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=209.85.128.67 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769452173; cv=none; b=MyJM7HBcB/wxPlnM5MRFVpCwYuUX5C51SU3BJn2mbssFI1ICbC7ouDCUoOpbJAJwTNF0UPo+zQiMXuzBCCoN+Wb1EY7HY2IdR8q1ViT4ERgrPd27LxXNTPM9lxoFu1Fhdovxg4RtBGEhKvx7mXz81WKK58DkfHzaV7BMAY/EGnw= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1769452173; c=relaxed/simple; bh=3H3+yn8WXYu5Gs0lLeCxy5v4rvhbQbhkVfLej3xS36Q=; h=Date:From:To:Cc:Subject:Message-ID:In-Reply-To:References: MIME-Version:Content-Type; b=c7wiwr3fitYa7sueGqCxtN7pfzErJ/5e/BGFcaNEePWMNBz5qCPaO3uHagBzgOQ5Y5CL4S4PiVV3jdwrMfluppc6ZPJ66OvjiOX0BwvBmfOz3X1pfnXgJ6ee3m6VQZBlH2OS1tWa0msBJtA2XEP/qPMPiEQw5xVd93ZDuOQ+WaU= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com; spf=pass smtp.mailfrom=gmail.com; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b=FQMfWedO; arc=none smtp.client-ip=209.85.128.67 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=gmail.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=gmail.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="FQMfWedO" Received: by mail-wm1-f67.google.com with SMTP id 5b1f17b1804b1-47ee4338e01so27567965e9.2 for ; Mon, 26 Jan 2026 10:29:31 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1769452170; x=1770056970; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:subject:cc:to:from:date:from:to:cc:subject:date :message-id:reply-to; bh=Te9h7VpASzTfI4+mQk0zlN73jH3YtGSUKimSiLG8R+E=; b=FQMfWedOM1WLoftv/xQyAXq1x9wzT+R5iUm+vt3VNYeDeK+C7eKnQ64/dR4GvabztB 8Flg4IR4MXQozvxtUQWYYF2OTwsPca6e03MoDdtkoDcrTiSVTWQdcVCwf993Kp28Hnqo SjwCB2+8bv90SMZFjwg9PARBI+nLBxf2SEO0KbGETiib0+moI0Q2tvRgiAw0xwln+K9O E2HHIdy8JviT1oHVSNNlTiUJTlJGBHbhCnoi8uZ/XZdmachojiIWo4WVkBTUgENj+Fko CtZOVwnG+4BHF+oOOmgDov5iDF6IFz/JrPMfPNLkMr6bgsBceC2HAECEc8mYFR6AoKbb tUqg== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1769452170; x=1770056970; h=content-transfer-encoding:mime-version:references:in-reply-to :message-id:subject:cc:to:from:date:x-gm-gg:x-gm-message-state:from :to:cc:subject:date:message-id:reply-to; bh=Te9h7VpASzTfI4+mQk0zlN73jH3YtGSUKimSiLG8R+E=; b=LfT4c5mLM5FxXYYu6+MkavJFhbfjK76XgKUoamQIwdktLifG3yMCiE75SisGS/5PKt 7NNn6D3U7Eqj/944FcLoGU/zDYsznDR6qqWHMyrDURgrx17bgyJXbfBVnq6ZTLAoBfj1 73Z4BkI0C+k+LAIFONyGCTMnkZkPMp6u0vuz6+ktV5fbvPpAg7S91c0XQ4rmKjBxsEtj GNZ9kJZOZamGtFdJDHVoAxsM2+2pbI3a2yMPCxHyIb+DisjtBzs4MvfO9xfPfOt5qnxV luyEJJJ69K+dMtdLVR9jxUzAkC3YJcTJgjeJWEARJ9AoWa96ro4e6YmC7Jwvwmes1fiw 10Vw== X-Forwarded-Encrypted: i=1; AJvYcCVfk0nRbmYF3GHKOWGafVu2OBQAwQL3kUBcz77llM9N9Ql4r+1/Gj2NsA88dcqC9uGgy2YTdfqjz9003lY=@vger.kernel.org X-Gm-Message-State: AOJu0YxRmKLeGzPyPIi5Zf4liFotia6mcR/1fIRtoi9YU8BClDDAF469 tc/5kS3VzHy5u7WvnZRSOwv+9FVziX1VXa08xwgHpWx/szCoHu+kgXK8 X-Gm-Gg: AZuq6aK5HDlkc//eNoJHipdUK/X9CYyvi/tdKjXUI4DQZUc0s2iMJU9lnfFjjcpwgnY NCWm6LZ7i5NPgBrZrOCxnw8u4xwpQK5pGLiMIdpQhsdzWBe6I//HFSnKWbcxZUDOuN0it44Jh5G ecKQ1FFXwz7dtkROBapnpgS+z04llWiGWkQNDzMzGC6i5PSfSnOI04LwHFfMgDb89p2sJunu+u0 sY2vLfbvTwVEktEsY949OOqOQfvPhX5Za6J52k9u+uNS++0kY1bA4NnsNmD6YQcsdEgLzKtAy6a PW5GyxpKPSnfMuMaB2uVBzl00qEQoP860C0DuhWFd8EmXKlwuN0cP5JgQsJztGRcjptzKaAc+jy 4JEn+pefvhcBtlUglkD5EWzSlXngmAxXwOpt86/uMMDh8k589AMxjbp9h6fShasXYw8/EcjgfS9 JZ69EhD6UTRHqeFLqFFGE/Lzej2TUHASY7t7r+vSS/UykK6zyAXYrA X-Received: by 2002:a05:600c:1d02:b0:480:1c10:5633 with SMTP id 5b1f17b1804b1-4805cf66b45mr87903825e9.26.1769452169869; Mon, 26 Jan 2026 10:29:29 -0800 (PST) Received: from pumpkin (82-69-66-36.dsl.in-addr.zen.co.uk. [82.69.66.36]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-48066be7404sm7185725e9.1.2026.01.26.10.29.29 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Mon, 26 Jan 2026 10:29:29 -0800 (PST) Date: Mon, 26 Jan 2026 18:29:28 +0000 From: David Laight To: David Yang Cc: netdev@vger.kernel.org, Aaron Conole , Eelco Chaudron , Ilya Maximets , "David S. Miller" , Eric Dumazet , Jakub Kicinski , Paolo Abeni , Simon Horman , dev@openvswitch.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH net-next v2 4/7] net: openvswitch: fix load tearing with u64_stats Message-ID: <20260126182928.39ab1d58@pumpkin> In-Reply-To: <20260123162159.2877941-5-mmyangfl@gmail.com> References: <20260123162159.2877941-1-mmyangfl@gmail.com> <20260123162159.2877941-5-mmyangfl@gmail.com> X-Mailer: Claws Mail 4.1.1 (GTK 3.24.38; arm-unknown-linux-gnueabihf) Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit On Sat, 24 Jan 2026 00:21:36 +0800 David Yang wrote: > On 64bit arches, struct u64_stats_sync is empty and provides no help > against load/store tearing. struct copying should not be considered > tear-free. Use u64_stats_reads() instead. Except that the compiler doesn't ever generate 'tearing accesses' for aligned 64bit accesses on any 64bit architecture. Similarly memcpy() won't generate problematic accesses. The problem is purely theoretical - the C language lets the compiler split accesses, but it doesn't. David > > Signed-off-by: David Yang > --- > net/openvswitch/datapath.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/net/openvswitch/datapath.c b/net/openvswitch/datapath.c > index d5b6e2002bc1..8ba94df7f942 100644 > --- a/net/openvswitch/datapath.c > +++ b/net/openvswitch/datapath.c > @@ -770,7 +770,8 @@ static void get_dp_stats(const struct datapath *dp, struct ovs_dp_stats *stats, > > do { > start = u64_stats_fetch_begin(&percpu_stats->syncp); > - local_stats = *percpu_stats; > + u64_stats_reads(&local_stats, percpu_stats, > + sizeof(local_stats)); > } while (u64_stats_fetch_retry(&percpu_stats->syncp, start)); > > stats->n_hit += local_stats.n_hit;