From owner-svn-src-all@freebsd.org Fri Sep 4 11:22:19 2020 Return-Path: Delivered-To: svn-src-all@mailman.nyi.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.nyi.freebsd.org (Postfix) with ESMTP id 20CFE3DDE0D; Fri, 4 Sep 2020 11:22:19 +0000 (UTC) (envelope-from mw@FreeBSD.org) Received: from mxrelay.nyi.freebsd.org (mxrelay.nyi.freebsd.org [IPv6:2610:1c1:1:606c::19:3]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256 client-signature RSA-PSS (4096 bits) client-digest SHA256) (Client CN "mxrelay.nyi.freebsd.org", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 4BjZyg0223z3cBt; Fri, 4 Sep 2020 11:22:19 +0000 (UTC) (envelope-from mw@FreeBSD.org) Received: from repo.freebsd.org (repo.freebsd.org [IPv6:2610:1c1:1:6068::e6a:0]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mxrelay.nyi.freebsd.org (Postfix) with ESMTPS id D96C5BF76; Fri, 4 Sep 2020 11:22:18 +0000 (UTC) (envelope-from mw@FreeBSD.org) Received: from repo.freebsd.org ([127.0.1.37]) by repo.freebsd.org (8.15.2/8.15.2) with ESMTP id 084BMIAO040629; Fri, 4 Sep 2020 11:22:18 GMT (envelope-from mw@FreeBSD.org) Received: (from mw@localhost) by repo.freebsd.org (8.15.2/8.15.2/Submit) id 084BMIYn040628; Fri, 4 Sep 2020 11:22:18 GMT (envelope-from mw@FreeBSD.org) Message-Id: <202009041122.084BMIYn040628@repo.freebsd.org> X-Authentication-Warning: repo.freebsd.org: mw set sender to mw@FreeBSD.org using -f From: Marcin Wojtas Date: Fri, 4 Sep 2020 11:22:18 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-stable@freebsd.org, svn-src-stable-12@freebsd.org Subject: svn commit: r365326 - stable/12/sys/sys X-SVN-Group: stable-12 X-SVN-Commit-Author: mw X-SVN-Commit-Paths: stable/12/sys/sys X-SVN-Commit-Revision: 365326 X-SVN-Commit-Repository: base MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: svn-src-all@freebsd.org X-Mailman-Version: 2.1.33 Precedence: list List-Id: "SVN commit messages for the entire src tree \(except for " user" and " projects" \)" List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Fri, 04 Sep 2020 11:22:19 -0000 Author: mw Date: Fri Sep 4 11:22:18 2020 New Revision: 365326 URL: https://svnweb.freebsd.org/changeset/base/365326 Log: MFC: r346593 Add barrier in buf ring peek function to prevent race in ARM and ARM64. Obtained from: Semihalf Sponsored by: Amazon, Inc. Modified: stable/12/sys/sys/buf_ring.h Directory Properties: stable/12/ (props changed) Modified: stable/12/sys/sys/buf_ring.h ============================================================================== --- stable/12/sys/sys/buf_ring.h Fri Sep 4 04:31:56 2020 (r365325) +++ stable/12/sys/sys/buf_ring.h Fri Sep 4 11:22:18 2020 (r365326) @@ -310,14 +310,23 @@ buf_ring_peek_clear_sc(struct buf_ring *br) if (!mtx_owned(br->br_lock)) panic("lock not held on single consumer dequeue"); #endif - /* - * I believe it is safe to not have a memory barrier - * here because we control cons and tail is worst case - * a lagging indicator so we worst case we might - * return NULL immediately after a buffer has been enqueued - */ + if (br->br_cons_head == br->br_prod_tail) return (NULL); + +#if defined(__arm__) || defined(__aarch64__) + /* + * The barrier is required there on ARM and ARM64 to ensure, that + * br->br_ring[br->br_cons_head] will not be fetched before the above + * condition is checked. + * Without the barrier, it is possible, that buffer will be fetched + * before the enqueue will put mbuf into br, then, in the meantime, the + * enqueue will update the array and the br_prod_tail, and the + * conditional check will be true, so we will return previously fetched + * (and invalid) buffer. + */ + atomic_thread_fence_acq(); +#endif #ifdef DEBUG_BUFRING /*