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=-0.6 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,FREEMAIL_FORGED_FROMDOMAIN,FREEMAIL_FROM, HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no 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 CA0A4C83009 for ; Tue, 28 Apr 2020 17:31:25 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id A8B17208E0 for ; Tue, 28 Apr 2020 17:31:25 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="Kpifsw0q" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728444AbgD1RbZ (ORCPT ); Tue, 28 Apr 2020 13:31:25 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:34418 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728225AbgD1RbY (ORCPT ); Tue, 28 Apr 2020 13:31:24 -0400 Received: from mail-pf1-x442.google.com (mail-pf1-x442.google.com [IPv6:2607:f8b0:4864:20::442]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C04E0C03C1AB; Tue, 28 Apr 2020 10:31:24 -0700 (PDT) Received: by mail-pf1-x442.google.com with SMTP id 18so9800069pfv.8; Tue, 28 Apr 2020 10:31:24 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=date:from:to:cc:subject:message-id:references:mime-version :content-disposition:in-reply-to; bh=o1hvJ7qJ286Xh+ZpEY5biAu9CzmRlIJ2PwFJ0cbItFo=; b=Kpifsw0qbOFcSjhI0V7+etB+KLPHGw7vdnW7iYqftCfWKdyVyHgS7FgTbbfRmV3PjD Twi1SLBi3v2UcidAh3om5V6LNNBvyqXspnH0nYPHG5hi4KuacYh4UBVDWQEufXrSA0R4 O/FKoxL+jL83PHfG9aqPJliWxrNbpfjIHtHamHyb3gmIkxOaib+CJj8tcX22Rh9kuzFU WRT6c4B3N0y0Y+yDP7CO6flNVQq+G2Xk7GzBse15i6AFLDmX7FpdpXrp7I2twStj4ZbT NEjDUAwAZEtiEh4gN5jmjC6xdVtwWba2fSZ1/nb6t+IKHKa2frsuukI2/474ejcDd9/e q4yA== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:date:from:to:cc:subject:message-id:references :mime-version:content-disposition:in-reply-to; bh=o1hvJ7qJ286Xh+ZpEY5biAu9CzmRlIJ2PwFJ0cbItFo=; b=P4p+zUPZ10qTBSAtJZzS3lQmsXDsiEQQ0KPoA7r/+Sg52uk7swwnHD5VMI3z1AS3uT Uu31e2yR/9aCQcF4e0Xq3BqeJRTXmuhXKSCWr3hED1/yeHpokRjTO9pOoOqRJN+L9lc9 HCmNPerkBGCp15wMS9597C2m9wIcJ8s3iZYiKlE6zQMH7GCcHOQ15VvjBYqQCLyn6o8I Q676zfF2AwCHqT+alFykhzICDpP9uPupm9yxgLh8yO6H/6EAeh9/i+F1txxwnCH/c2Hc O+j3iVmtrgln200jAOWEb2KUTRmwn+rurRvziXd9SPMEcL3j9BOQ5sL9VfbCTgZtEZje jkiw== X-Gm-Message-State: AGi0PuYh0isbQmv8C5oPtbe/P7aSiZTxb0Nu1FDjomHxMVoB9u09ad5D nWjOKbhocE8X8mwbYuWzIkw= X-Google-Smtp-Source: APiQypIRVSOGKZHDBB5yU/ZOWxmZRb3LKojyM0t6qFlCW4oiGl8ytR6ak7C9j2SkMGv+y1vQMXugZQ== X-Received: by 2002:a63:63c1:: with SMTP id x184mr14465633pgb.116.1588095084126; Tue, 28 Apr 2020 10:31:24 -0700 (PDT) Received: from ast-mbp.dhcp.thefacebook.com ([2620:10d:c090:400::5:9061]) by smtp.gmail.com with ESMTPSA id c28sm15588485pfp.200.2020.04.28.10.31.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Tue, 28 Apr 2020 10:31:23 -0700 (PDT) Date: Tue, 28 Apr 2020 10:31:20 -0700 From: Alexei Starovoitov To: Andrii Nakryiko Cc: bpf@vger.kernel.org, netdev@vger.kernel.org, ast@fb.com, daniel@iogearbox.net, andrii.nakryiko@gmail.com, kernel-team@fb.com Subject: Re: [PATCH v2 bpf-next 02/10] bpf: allocate ID for bpf_link Message-ID: <20200428173120.lof25gzz75bx5ot7@ast-mbp.dhcp.thefacebook.com> References: <20200428054944.4015462-1-andriin@fb.com> <20200428054944.4015462-3-andriin@fb.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200428054944.4015462-3-andriin@fb.com> Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@vger.kernel.org On Mon, Apr 27, 2020 at 10:49:36PM -0700, Andrii Nakryiko wrote: > +int bpf_link_settle(struct bpf_link_primer *primer) > +{ > + /* make bpf_link fetchable by ID */ > + WRITE_ONCE(primer->link->id, primer->id); what does WRITE_ONCE serve here? bpf_link_settle can only be called at the end of attach. If attach is slow than parallel get_fd_by_id can get an new FD instance for link with zero id. In such case deref of link->id will race with above assignment? But I don't see READ_ONCE in patch 3. It's under link_idr_lock there. How about grabbing link_idr_lock here as well ? otherwise it's still racy since WRITE_ONCE is not paired. The mix of spin_lock_irqsave(&link_idr_lock) and spin_lock_bh(&link_idr_lock) looks weird. We do the same for map_idr because maps have complicated freeing logic, but prog_idr is consistent. If you see the need for irqsave variant then please use it in all cases.