From owner-svn-src-all@freebsd.org Wed Jun 6 12:57:13 2018 Return-Path: Delivered-To: svn-src-all@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2610:1c1:1:606c::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 07413FF51A2; Wed, 6 Jun 2018 12:57:13 +0000 (UTC) (envelope-from jhibbits@FreeBSD.org) Received: from mxrelay.nyi.freebsd.org (mxrelay.nyi.freebsd.org [IPv6:2610:1c1:1:606c::19:3]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client CN "mxrelay.nyi.freebsd.org", Issuer "Let's Encrypt Authority X3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id A9F1472E65; Wed, 6 Jun 2018 12:57:12 +0000 (UTC) (envelope-from jhibbits@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 86EE030E4; Wed, 6 Jun 2018 12:57:12 +0000 (UTC) (envelope-from jhibbits@FreeBSD.org) Received: from repo.freebsd.org ([127.0.1.37]) by repo.freebsd.org (8.15.2/8.15.2) with ESMTP id w56CvCcb089370; Wed, 6 Jun 2018 12:57:12 GMT (envelope-from jhibbits@FreeBSD.org) Received: (from jhibbits@localhost) by repo.freebsd.org (8.15.2/8.15.2/Submit) id w56CvCwq089369; Wed, 6 Jun 2018 12:57:12 GMT (envelope-from jhibbits@FreeBSD.org) Message-Id: <201806061257.w56CvCwq089369@repo.freebsd.org> X-Authentication-Warning: repo.freebsd.org: jhibbits set sender to jhibbits@FreeBSD.org using -f From: Justin Hibbits Date: Wed, 6 Jun 2018 12:57:12 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r334708 - head/sys/kern X-SVN-Group: head X-SVN-Commit-Author: jhibbits X-SVN-Commit-Paths: head/sys/kern X-SVN-Commit-Revision: 334708 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: 2.1.26 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: Wed, 06 Jun 2018 12:57:13 -0000 Author: jhibbits Date: Wed Jun 6 12:57:11 2018 New Revision: 334708 URL: https://svnweb.freebsd.org/changeset/base/334708 Log: Add a memory barrier after taking a reference on the vnode holdcnt in _vhold This is needed to avoid a race between the VNASSERT() below, and another thread updating the VI_FREE flag, on weakly-ordered architectures. On a 72-thread POWER9, without this barrier a 'make -j72 buildworld' would panic on the assert regularly. It may be possible to use a weaker barrier, and I'll investigate that once all stability issues are worked out on POWER9. Modified: head/sys/kern/vfs_subr.c Modified: head/sys/kern/vfs_subr.c ============================================================================== --- head/sys/kern/vfs_subr.c Wed Jun 6 10:46:24 2018 (r334707) +++ head/sys/kern/vfs_subr.c Wed Jun 6 12:57:11 2018 (r334708) @@ -2807,6 +2807,9 @@ _vhold(struct vnode *vp, bool locked) CTR2(KTR_VFS, "%s: vp %p", __func__, vp); if (!locked) { if (refcount_acquire_if_not_zero(&vp->v_holdcnt)) { +#if !defined(__amd64__) && !defined(__i386__) + mb(); +#endif VNASSERT((vp->v_iflag & VI_FREE) == 0, vp, ("_vhold: vnode with holdcnt is free")); return;