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 X-Spam-Level: X-Spam-Status: No, score=-16.2 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_CR_TRAILER,INCLUDES_PATCH, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 9E753C48BCD for ; Wed, 9 Jun 2021 13:57:27 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 7D6C4613AD for ; Wed, 9 Jun 2021 13:57:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236986AbhFIN7U (ORCPT ); Wed, 9 Jun 2021 09:59:20 -0400 Received: from mail.kernel.org ([198.145.29.99]:59830 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S236957AbhFIN7T (ORCPT ); Wed, 9 Jun 2021 09:59:19 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id B032A61246; Wed, 9 Jun 2021 13:57:24 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1623247044; bh=h6g0gYfjXeaCXXJ7vgG0rGy7l3BHXfQOCyFfliJl32I=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=tmtk8KXnN5AhZzrC8ww4TjwEzMWEcTZWQd6TPHhHz0B1zAV7hsOg/Cy3WPa92O3fj m7+EuJBy1l3hJ1DaYec5iiNt+u1QZXokMltMehUd3E/b5X5OSxziTwKFtdY6HGI8wE ybFEXWD7xB43fhOKfff4kFJeGfgbf49O7uxDm4/5l1EXgmaldWnQL4Pr5UfpbhM3nG lrX7v/b0UNWm4xcYUzi8KlJnm/6ZjZT0m1ZwTQsfGhSEXaf4TW81wCKcTlko5bm488 fLC5RpX+S26wAPgqf1ZTF1t5qP1tHVeUR5Tm9w/fphmnH+suo3TuVWWZlGqt/ieZA2 +jvwPWFYSJ2wA== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id 81E985C039E; Wed, 9 Jun 2021 06:57:24 -0700 (PDT) Date: Wed, 9 Jun 2021 06:57:24 -0700 From: "Paul E. McKenney" To: Toke =?iso-8859-1?Q?H=F8iland-J=F8rgensen?= Cc: bpf@vger.kernel.org, netdev@vger.kernel.org, Martin KaFai Lau , Hangbin Liu , Jesper Dangaard Brouer , Magnus Karlsson , Guy Tzalik , Saeed Bishara Subject: Re: [PATCH bpf-next 05/17] ena: remove rcu_read_lock() around XDP program invocation Message-ID: <20210609135724.GB4397@paulmck-ThinkPad-P17-Gen-1> Reply-To: paulmck@kernel.org References: <20210609103326.278782-1-toke@redhat.com> <20210609103326.278782-6-toke@redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-1 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <20210609103326.278782-6-toke@redhat.com> Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org On Wed, Jun 09, 2021 at 12:33:14PM +0200, Toke Høiland-Jørgensen wrote: > The ena driver has rcu_read_lock()/rcu_read_unlock() pairs around XDP > program invocations. However, the actual lifetime of the objects referred > by the XDP program invocation is longer, all the way through to the call to > xdp_do_flush(), making the scope of the rcu_read_lock() too small. This > turns out to be harmless because it all happens in a single NAPI poll > cycle (and thus under local_bh_disable()), but it makes the rcu_read_lock() > misleading. > > Rather than extend the scope of the rcu_read_lock(), just get rid of it > entirely. With the addition of RCU annotations to the XDP_REDIRECT map > types that take bh execution into account, lockdep even understands this to > be safe, so there's really no reason to keep it around. It might be worth adding a comment, perhaps where the rcu_read_lock() used to be, stating what the protection is. Maybe something like this? /* * This code is invoked within a single NAPI poll cycle * and thus under local_bh_disable(), which provides the * needed RCU protection. */ Thanx, Paul > Cc: Guy Tzalik > Cc: Saeed Bishara > Signed-off-by: Toke Høiland-Jørgensen > --- > drivers/net/ethernet/amazon/ena/ena_netdev.c | 3 --- > 1 file changed, 3 deletions(-) > > diff --git a/drivers/net/ethernet/amazon/ena/ena_netdev.c b/drivers/net/ethernet/amazon/ena/ena_netdev.c > index 881f88754bf6..a4378b14af4c 100644 > --- a/drivers/net/ethernet/amazon/ena/ena_netdev.c > +++ b/drivers/net/ethernet/amazon/ena/ena_netdev.c > @@ -385,7 +385,6 @@ static int ena_xdp_execute(struct ena_ring *rx_ring, struct xdp_buff *xdp) > u64 *xdp_stat; > int qid; > > - rcu_read_lock(); > xdp_prog = READ_ONCE(rx_ring->xdp_bpf_prog); > > if (!xdp_prog) > @@ -443,8 +442,6 @@ static int ena_xdp_execute(struct ena_ring *rx_ring, struct xdp_buff *xdp) > > ena_increase_stat(xdp_stat, 1, &rx_ring->syncp); > out: > - rcu_read_unlock(); > - > return verdict; > } > > -- > 2.31.1 >