From owner-dev-commits-src-branches@freebsd.org Wed Mar 3 00:35:31 2021 Return-Path: Delivered-To: dev-commits-src-branches@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 34C5F5570B2; Wed, 3 Mar 2021 00:35:31 +0000 (UTC) (envelope-from git@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 "R3" (verified OK)) by mx1.freebsd.org (Postfix) with ESMTPS id 4Dqw5F35Ghz3rf2; Wed, 3 Mar 2021 00:35:29 +0000 (UTC) (envelope-from git@FreeBSD.org) Received: from gitrepo.freebsd.org (gitrepo.freebsd.org [IPv6:2610:1c1:1:6068::e6a:5]) (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 did not present a certificate) by mxrelay.nyi.freebsd.org (Postfix) with ESMTPS id 322AE202E8; Wed, 3 Mar 2021 00:35:29 +0000 (UTC) (envelope-from git@FreeBSD.org) Received: from gitrepo.freebsd.org ([127.0.1.44]) by gitrepo.freebsd.org (8.16.1/8.16.1) with ESMTP id 1230ZTgN080915; Wed, 3 Mar 2021 00:35:29 GMT (envelope-from git@gitrepo.freebsd.org) Received: (from git@localhost) by gitrepo.freebsd.org (8.16.1/8.16.1/Submit) id 1230ZT98080914; Wed, 3 Mar 2021 00:35:29 GMT (envelope-from git) Date: Wed, 3 Mar 2021 00:35:29 GMT Message-Id: <202103030035.1230ZT98080914@gitrepo.freebsd.org> To: src-committers@FreeBSD.org, dev-commits-src-all@FreeBSD.org, dev-commits-src-branches@FreeBSD.org From: Mark Johnston Subject: git: c29d3ecdc8b3 - stable/13 - rmlock: Add a required compiler membar to the rlock slow path MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit X-Git-Committer: markj X-Git-Repository: src X-Git-Refname: refs/heads/stable/13 X-Git-Reftype: branch X-Git-Commit: c29d3ecdc8b3903d812c0467319ced6f85872d0e Auto-Submitted: auto-generated X-BeenThere: dev-commits-src-branches@freebsd.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: Commits to the stable branches of the FreeBSD src repository List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 03 Mar 2021 00:35:31 -0000 The branch stable/13 has been updated by markj: URL: https://cgit.FreeBSD.org/src/commit/?id=c29d3ecdc8b3903d812c0467319ced6f85872d0e commit c29d3ecdc8b3903d812c0467319ced6f85872d0e Author: Mark Johnston AuthorDate: 2021-02-24 02:15:50 +0000 Commit: Mark Johnston CommitDate: 2021-03-03 00:34:11 +0000 rmlock: Add a required compiler membar to the rlock slow path The tracker flags need to be loaded only after the tracker is removed from its per-CPU queue. Otherwise, readers may fail to synchronize with pending writers attempting to propagate priority to active readers, and readers and writers deadlock on each other. This was observed in a stable/12-based armv7 kernel where the compiler had reordered the load of rmp_flags to before the stores updating the queue. Reviewed by: rlibby, scottl Discussed with: kib Sponsored by: Rubicon Communications, LLC ("Netgate") Differential Revision: https://reviews.freebsd.org/D28821 (cherry picked from commit 1d44514fcd68809cfd493a7352ace29ddad443d6) --- sys/kern/kern_rmlock.c | 6 +++++- 1 file changed, 5 insertions(+), 1 deletion(-) diff --git a/sys/kern/kern_rmlock.c b/sys/kern/kern_rmlock.c index 401445d3d03f..9135709d88cf 100644 --- a/sys/kern/kern_rmlock.c +++ b/sys/kern/kern_rmlock.c @@ -362,7 +362,11 @@ _rm_rlock_hard(struct rmlock *rm, struct rm_priotracker *tracker, int trylock) /* Remove our tracker from the per-cpu list. */ rm_tracker_remove(pc, tracker); - /* Check to see if the IPI granted us the lock after all. */ + /* + * Check to see if the IPI granted us the lock after all. The load of + * rmp_flags must happen after the tracker is removed from the list. + */ + __compiler_membar(); if (tracker->rmp_flags) { /* Just add back tracker - we hold the lock. */ rm_tracker_add(pc, tracker);