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=-0.8 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,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 EE0A7ECDFAA for ; Mon, 16 Jul 2018 22:30:24 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 97DB1208E8 for ; Mon, 16 Jul 2018 22:30:24 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 97DB1208E8 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=iogearbox.net Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730371AbeGPW7u (ORCPT ); Mon, 16 Jul 2018 18:59:50 -0400 Received: from www62.your-server.de ([213.133.104.62]:40060 "EHLO www62.your-server.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728524AbeGPW7u (ORCPT ); Mon, 16 Jul 2018 18:59:50 -0400 Received: from [88.198.220.130] (helo=sslproxy01.your-server.de) by www62.your-server.de with esmtpsa (TLSv1.2:DHE-RSA-AES256-GCM-SHA384:256) (Exim 4.85_2) (envelope-from ) id 1ffC0Z-0006uN-5I; Tue, 17 Jul 2018 00:30:19 +0200 Received: from [62.203.87.61] (helo=linux.home) by sslproxy01.your-server.de with esmtpsa (TLSv1.2:ECDHE-RSA-AES256-GCM-SHA384:256) (Exim 4.89) (envelope-from ) id 1ffC0Y-0000ui-UC; Tue, 17 Jul 2018 00:30:19 +0200 Subject: Re: [PATCH v2 bpf 3/5] bpf: bpf_prog_array_free() should take a generic non-rcu pointer To: Roman Gushchin , netdev@vger.kernel.org Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com, Alexei Starovoitov References: <20180713194114.2711-1-guro@fb.com> <20180713194114.2711-3-guro@fb.com> From: Daniel Borkmann Message-ID: <41b5f919-3155-5bd4-2774-84efd58650e2@iogearbox.net> Date: Tue, 17 Jul 2018 00:30:18 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:52.0) Gecko/20100101 Thunderbird/52.3.0 MIME-Version: 1.0 In-Reply-To: <20180713194114.2711-3-guro@fb.com> Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 7bit X-Authenticated-Sender: daniel@iogearbox.net X-Virus-Scanned: Clear (ClamAV 0.100.0/24759/Mon Jul 16 22:54:23 2018) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 07/13/2018 09:41 PM, Roman Gushchin wrote: > bpf_prog_array_free() should take a generic non-rcu pointer > as an argument, as freeing the objects assumes that we're > holding an exclusive rights on it. > > rcu_access_pointer() can be used to convert a __rcu pointer to > a generic pointer before passing it to bpf_prog_array_free(), > if necessary. > > This patch eliminates the following sparse warning: > kernel/bpf/core.c:1556:9: warning: incorrect type in argument 1 (different address spaces) > kernel/bpf/core.c:1556:9: expected struct callback_head *head > kernel/bpf/core.c:1556:9: got struct callback_head [noderef] * > > Fixes: 324bda9e6c5a ("bpf: multi program support for cgroup+bpf") > Signed-off-by: Roman Gushchin > Cc: Alexei Starovoitov > Cc: Daniel Borkmann > --- > drivers/media/rc/bpf-lirc.c | 6 +++--- > include/linux/bpf.h | 2 +- > kernel/bpf/cgroup.c | 11 ++++++----- > kernel/bpf/core.c | 5 ++--- > kernel/trace/bpf_trace.c | 8 ++++---- > 5 files changed, 16 insertions(+), 16 deletions(-) > > diff --git a/drivers/media/rc/bpf-lirc.c b/drivers/media/rc/bpf-lirc.c > index fcfab6635f9c..509b262aa0dc 100644 > --- a/drivers/media/rc/bpf-lirc.c > +++ b/drivers/media/rc/bpf-lirc.c > @@ -135,7 +135,7 @@ static int lirc_bpf_attach(struct rc_dev *rcdev, struct bpf_prog *prog) > goto unlock; > > rcu_assign_pointer(raw->progs, new_array); > - bpf_prog_array_free(old_array); > + bpf_prog_array_free(rcu_access_pointer(old_array)); Taking this one as an example, why can't we already do the rcu_dereference() on the 'old_array = raw->progs' where we fetch the old_array initially? Then we also wouldn't need the rcu_access_pointer() on bpf_prog_array_free() and yet another rcu_dereference() inside the bpf_prog_array_copy() from your later patch? Regarding former, rcu_access_pointer() should also only be used for testing the pointer value, but deeper in bpf_prog_array_free() we also deref it, etc. > unlock: > mutex_unlock(&ir_raw_handler_lock); > @@ -173,7 +173,7 @@ static int lirc_bpf_detach(struct rc_dev *rcdev, struct bpf_prog *prog) > goto unlock; > > rcu_assign_pointer(raw->progs, new_array); > - bpf_prog_array_free(old_array); > + bpf_prog_array_free(rcu_access_pointer(old_array)); > unlock: > mutex_unlock(&ir_raw_handler_lock); > return ret; > @@ -204,7 +204,7 @@ void lirc_bpf_free(struct rc_dev *rcdev) > while (*progs) > bpf_prog_put(*progs++); > > - bpf_prog_array_free(rcdev->raw->progs); > + bpf_prog_array_free(rcu_access_pointer(rcdev->raw->progs)); > }