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=-15.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_CR_TRAILER,INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED 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 41F53C48BD1 for ; Thu, 10 Jun 2021 23:05:44 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 26B6B613E1 for ; Thu, 10 Jun 2021 23:05:44 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230248AbhFJXHk (ORCPT ); Thu, 10 Jun 2021 19:07:40 -0400 Received: from us-smtp-delivery-124.mimecast.com ([170.10.133.124]:27492 "EHLO us-smtp-delivery-124.mimecast.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230103AbhFJXHk (ORCPT ); Thu, 10 Jun 2021 19:07:40 -0400 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1623366342; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=zaN/4xw50VkDE65M8AibghHcVWhVfVwq3dgmOVKPedk=; b=bhtMle334M4N1NOzw2Brpa1MYz0ModuMllJUlNoO/+mIUbLDcOLKBqpP8CgkY7Ch6zCQzC 58BT8pnOh8mCH9cHdZYzR6gvx2RQTmDeof+h5BSNHvcHExwjK4BosiU789cRuqo1J0i9Mn NV9nCL98CadvnBKH3nLqHRy0+MIy4RY= Received: from mail-ed1-f72.google.com (mail-ed1-f72.google.com [209.85.208.72]) (Using TLS) by relay.mimecast.com with ESMTP id us-mta-480-5-S0vcYUMaCzwbtXHN2RmA-1; Thu, 10 Jun 2021 19:05:41 -0400 X-MC-Unique: 5-S0vcYUMaCzwbtXHN2RmA-1 Received: by mail-ed1-f72.google.com with SMTP id j13-20020aa7de8d0000b029038fc8e57037so15023738edv.0 for ; Thu, 10 Jun 2021 16:05:41 -0700 (PDT) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:in-reply-to:references:date :message-id:mime-version:content-transfer-encoding; bh=zaN/4xw50VkDE65M8AibghHcVWhVfVwq3dgmOVKPedk=; b=DQI1B2wsIJ0cNZpB8JWfQyjrGhPjU4KEUET9K0s/ep4fifgCsCZRTPX2ZMpRcjITwJ 0mObMU1fFxq8P5VNrLlOc18BwLgu+vKPJ1ZZneOBYqTl5IFTQocdo6cOAwfuZxGAPk9v r6gh8BK2lr2h/KnfPG5Zp3FIxsbWkBWogWizsLtd8UiBItb3u65TPnd/e5uaG03cy9M6 xH44SnasYcLkGrwUFxrzoFXNO1E9/+ITUg8fFDOi6kcdJJSqeWpQESXNaVrswkod6B2X cSgRsWve+a2bxxLLW9S5UW0lofZR3B8S3wtRANIW+KizIQc79hTolFXN19qel1BZgFBj 6uMg== X-Gm-Message-State: AOAM531syDwVFCaOORMKY7bFgG/y7pNTQOeum1CDH8NszI1H/Q7LYVMj Rd0zLg02jrt5soeBRfOPmv4FNhxYkfp+Fmx0iMAHEbsymTjts4TvuoeFzp/327bbuAhgKnKrxrA YhXZiPEjMXulV X-Received: by 2002:aa7:c9cf:: with SMTP id i15mr788025edt.118.1623366340323; Thu, 10 Jun 2021 16:05:40 -0700 (PDT) X-Google-Smtp-Source: ABdhPJz7UrdC3NbigfdW/whZC2A9NUxkEVZp/6LZemrS5UvqVh5wxoS0Eay52k4MdJevVhm+NwJX1Q== X-Received: by 2002:aa7:c9cf:: with SMTP id i15mr788003edt.118.1623366339966; Thu, 10 Jun 2021 16:05:39 -0700 (PDT) Received: from alrua-x1.borgediget.toke.dk ([2a0c:4d80:42:443::2]) by smtp.gmail.com with ESMTPSA id de19sm2016257edb.70.2021.06.10.16.05.39 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 10 Jun 2021 16:05:39 -0700 (PDT) Received: by alrua-x1.borgediget.toke.dk (Postfix, from userid 1000) id A3A1818071E; Fri, 11 Jun 2021 01:05:38 +0200 (CEST) From: Toke =?utf-8?Q?H=C3=B8iland-J=C3=B8rgensen?= To: Martin KaFai Lau Cc: bpf@vger.kernel.org, netdev@vger.kernel.org, Hangbin Liu , Jesper Dangaard Brouer , Magnus Karlsson , "Paul E . McKenney" Subject: Re: [PATCH bpf-next 03/17] dev: add rcu_read_lock_bh_held() as a valid check when getting a RCU dev ref In-Reply-To: <20210610193722.753tqgrovwyg2v6v@kafai-mbp> References: <20210609103326.278782-1-toke@redhat.com> <20210609103326.278782-4-toke@redhat.com> <20210610193722.753tqgrovwyg2v6v@kafai-mbp> X-Clacks-Overhead: GNU Terry Pratchett Date: Fri, 11 Jun 2021 01:05:38 +0200 Message-ID: <87lf7huxq5.fsf@toke.dk> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable Precedence: bulk List-ID: X-Mailing-List: bpf@vger.kernel.org Martin KaFai Lau writes: > On Wed, Jun 09, 2021 at 12:33:12PM +0200, Toke H=C3=B8iland-J=C3=B8rgense= n wrote: >> Some of the XDP helpers (in particular, xdp_do_redirect()) will get a >> struct net_device reference using dev_get_by_index_rcu(). These are call= ed >> from a NAPI poll context, which means the RCU reference liveness is ensu= red >> by local_bh_disable(). Add rcu_read_lock_bh_held() as a condition to the >> RCU list traversal in dev_get_by_index_rcu() so lockdep understands that >> the dereferences are safe from *both* an rcu_read_lock() *and* with >> local_bh_disable(). >>=20 >> Signed-off-by: Toke H=C3=B8iland-J=C3=B8rgensen >> --- >> net/core/dev.c | 2 +- >> 1 file changed, 1 insertion(+), 1 deletion(-) >>=20 >> diff --git a/net/core/dev.c b/net/core/dev.c >> index febb23708184..a499c5ffe4a5 100644 >> --- a/net/core/dev.c >> +++ b/net/core/dev.c >> @@ -1002,7 +1002,7 @@ struct net_device *dev_get_by_index_rcu(struct net= *net, int ifindex) >> struct net_device *dev; >> struct hlist_head *head =3D dev_index_hash(net, ifindex); >>=20=20 >> - hlist_for_each_entry_rcu(dev, head, index_hlist) >> + hlist_for_each_entry_rcu(dev, head, index_hlist, rcu_read_lock_bh_held= ()) > Is it needed? hlist_for_each_entry_rcu() checks for > rcu_read_lock_any_held(). Did lockdep complain? Ah, yes, I think you're right. I totally missed that rcu_read_lock_any_held() includes a '!preemptible()' check at the end. I'll drop this patch, then! -Toke