From owner-svn-src-stable-12@freebsd.org Tue Dec 15 21:52:32 2020 Return-Path: Delivered-To: svn-src-stable-12@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 60B294C5326; Tue, 15 Dec 2020 21:52:32 +0000 (UTC) (envelope-from kevans@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 4CwX6m2MRJz3FW5; Tue, 15 Dec 2020 21:52:32 +0000 (UTC) (envelope-from kevans@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 43E2F1B2D2; Tue, 15 Dec 2020 21:52:32 +0000 (UTC) (envelope-from kevans@FreeBSD.org) Received: from repo.freebsd.org ([127.0.1.37]) by repo.freebsd.org (8.15.2/8.15.2) with ESMTP id 0BFLqWha053035; Tue, 15 Dec 2020 21:52:32 GMT (envelope-from kevans@FreeBSD.org) Received: (from kevans@localhost) by repo.freebsd.org (8.15.2/8.15.2/Submit) id 0BFLqWL1053034; Tue, 15 Dec 2020 21:52:32 GMT (envelope-from kevans@FreeBSD.org) Message-Id: <202012152152.0BFLqWL1053034@repo.freebsd.org> X-Authentication-Warning: repo.freebsd.org: kevans set sender to kevans@FreeBSD.org using -f From: Kyle Evans Date: Tue, 15 Dec 2020 21:52:32 +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: r368680 - stable/12/sys/kern X-SVN-Group: stable-12 X-SVN-Commit-Author: kevans X-SVN-Commit-Paths: stable/12/sys/kern X-SVN-Commit-Revision: 368680 X-SVN-Commit-Repository: base MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit X-BeenThere: svn-src-stable-12@freebsd.org X-Mailman-Version: 2.1.34 Precedence: list List-Id: SVN commit messages for only the 12-stable src tree List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 15 Dec 2020 21:52:32 -0000 Author: kevans Date: Tue Dec 15 21:52:31 2020 New Revision: 368680 URL: https://svnweb.freebsd.org/changeset/base/368680 Log: MFC r368461: kern: cpuset: resolve race between cpuset_lookup/cpuset_rel The race plays out like so between threads A and B: 1. A ref's cpuset 10 2. B does a lookup of cpuset 10, grabs the cpuset lock and searches cpuset_ids 3. A rel's cpuset 10 and observes the last ref, waits on the cpuset lock while B is still searching and not yet ref'd 4. B ref's cpuset 10 and drops the cpuset lock 5. A proceeds to free the cpuset out from underneath B Resolve the race by only releasing the last reference under the cpuset lock. Thread A now picks up the spinlock and observes that the cpuset has been revived, returning immediately for B to deal with later. Modified: stable/12/sys/kern/kern_cpuset.c Directory Properties: stable/12/ (props changed) Modified: stable/12/sys/kern/kern_cpuset.c ============================================================================== --- stable/12/sys/kern/kern_cpuset.c Tue Dec 15 21:51:45 2020 (r368679) +++ stable/12/sys/kern/kern_cpuset.c Tue Dec 15 21:52:31 2020 (r368680) @@ -207,9 +207,13 @@ cpuset_rel(struct cpuset *set) { cpusetid_t id; - if (refcount_release(&set->cs_ref) == 0) + if (refcount_release_if_not_last(&set->cs_ref)) return; mtx_lock_spin(&cpuset_lock); + if (!refcount_release(&set->cs_ref)) { + mtx_unlock_spin(&cpuset_lock); + return; + } LIST_REMOVE(set, cs_siblings); id = set->cs_id; if (id != CPUSET_INVALID) @@ -229,9 +233,13 @@ static void cpuset_rel_defer(struct setlist *head, struct cpuset *set) { - if (refcount_release(&set->cs_ref) == 0) + if (refcount_release_if_not_last(&set->cs_ref)) return; mtx_lock_spin(&cpuset_lock); + if (!refcount_release(&set->cs_ref)) { + mtx_unlock_spin(&cpuset_lock); + return; + } LIST_REMOVE(set, cs_siblings); if (set->cs_id != CPUSET_INVALID) LIST_REMOVE(set, cs_link);