From patchwork Thu Aug 27 22:32:47 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Jakub Kicinski X-Patchwork-Id: 1352931 Return-Path: X-Original-To: patchwork-incoming-netdev@ozlabs.org Delivered-To: patchwork-incoming-netdev@ozlabs.org Authentication-Results: ozlabs.org; spf=pass (sender SPF authorized) smtp.mailfrom=vger.kernel.org (client-ip=23.128.96.18; helo=vger.kernel.org; envelope-from=netdev-owner@vger.kernel.org; receiver=) Authentication-Results: ozlabs.org; dmarc=pass (p=none dis=none) header.from=kernel.org Authentication-Results: ozlabs.org; dkim=pass (1024-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.a=rsa-sha256 header.s=default header.b=FIQBbd/x; dkim-atps=neutral Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by ozlabs.org (Postfix) with ESMTP id 4BcyDW6SsRz9sPB for ; Fri, 28 Aug 2020 08:33:15 +1000 (AEST) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727912AbgH0WdO (ORCPT ); Thu, 27 Aug 2020 18:33:14 -0400 Received: from mail.kernel.org ([198.145.29.99]:49504 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726953AbgH0WdN (ORCPT ); Thu, 27 Aug 2020 18:33:13 -0400 Received: from kicinski-fedora-PC1C0HJN.thefacebook.com (unknown [163.114.132.6]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 0F5832080C; Thu, 27 Aug 2020 22:33:13 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1598567593; bh=+CIrDgdDkye3H5KyAO4tjJU03XWNTqZfgPKrajTglWY=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=FIQBbd/xdlBXD0KQpN796prHD9FtQL6wnTs65xFgUrTFo+l5Zm1knqKv4KLypNgs4 bQxyH5Zp+9/xlqj8oH5aJ3ZN6kvOHW79zQc6IZDZWZ8Lv6+hocU9W71RBPjHofaiYt CQzU4Ok91Z/wC1O5WG8/IqaCY95j63ZzF5a6cOMY= From: Jakub Kicinski To: eric.dumazet@gmail.com Cc: davem@davemloft.net, netdev@vger.kernel.org, kernel-team@fb.com, Jakub Kicinski Subject: [RFC -next 0/3] Re: [PATCH net 1/2] net: disable netpoll on fresh napis Date: Thu, 27 Aug 2020 15:32:47 -0700 Message-Id: <20200827223250.2045503-1-kuba@kernel.org> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200827104753.29d836bb@kicinski-fedora-PC1C0HJN> References: <20200827104753.29d836bb@kicinski-fedora-PC1C0HJN> MIME-Version: 1.0 Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Thu, 27 Aug 2020 10:47:53 -0700 Jakub Kicinski wrote: > > Oh, I really thought list_for_each_entry_rcu() was only checking standard rcu. > > > > I might have been confused because we do have hlist_for_each_entry_rcu_bh() helper. > > > > Anyway, when looking at the patch I was not at ease because we do not have proper > > rcu grace period when a napi is removed from dev->napi_list. A driver might > > free the napi struct right after calling netif_napi_del() > > Ugh, you're right. I didn't look closely enough at netif_napi_del(): > > if (napi_hash_del(napi)) > synchronize_net(); > list_del_init(&napi->dev_list); > > Looks like I can reorder these.. and perhaps make all dev->napi_list > accesses RCU, for netpoll? So I had a look and looks like some reshuffling may be required to get out of this pickle. The objective is for drivers to observe RCU grace period after netif_napi_del() not just napi_hash_del(). Sending as RFC because IDK if the churn vs improvement ratio is acceptable here. Jakub Kicinski (3): net: remove napi_hash_del() from driver-facing API net: manage napi add/del idempotence explicitly net: make sure napi_list is safe for RCU traversal .../net/ethernet/broadcom/bnx2x/bnx2x_cmn.h | 8 ++--- drivers/net/ethernet/broadcom/bnxt/bnxt.c | 5 ++- drivers/net/ethernet/cisco/enic/enic_main.c | 12 ++++--- drivers/net/ethernet/intel/ixgbe/ixgbe_lib.c | 4 +-- .../net/ethernet/myricom/myri10ge/myri10ge.c | 5 ++- drivers/net/veth.c | 3 +- drivers/net/virtio_net.c | 7 ++-- include/linux/netdevice.h | 36 +++++++++---------- net/core/dev.c | 32 ++++++++--------- net/core/netpoll.c | 2 +- 10 files changed, 55 insertions(+), 59 deletions(-)