From owner-svn-src-all@FreeBSD.ORG Tue Jun 17 08:02:51 2014 Return-Path: Delivered-To: svn-src-all@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [8.8.178.115]) (using TLSv1 with cipher ADH-AES256-SHA (256/256 bits)) (No client certificate requested) by hub.freebsd.org (Postfix) with ESMTPS id E901918A; Tue, 17 Jun 2014 08:02:51 +0000 (UTC) Received: from svn.freebsd.org (svn.freebsd.org [IPv6:2001:1900:2254:2068::e6a:0]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id B9F3420E5; Tue, 17 Jun 2014 08:02:51 +0000 (UTC) Received: from svn.freebsd.org ([127.0.1.70]) by svn.freebsd.org (8.14.8/8.14.8) with ESMTP id s5H82pRM030087; Tue, 17 Jun 2014 08:02:51 GMT (envelope-from delphij@svn.freebsd.org) Received: (from delphij@localhost) by svn.freebsd.org (8.14.8/8.14.8/Submit) id s5H82pEh030086; Tue, 17 Jun 2014 08:02:51 GMT (envelope-from delphij@svn.freebsd.org) Message-Id: <201406170802.s5H82pEh030086@svn.freebsd.org> From: Xin LI Date: Tue, 17 Jun 2014 08:02:51 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-vendor@freebsd.org Subject: svn commit: r267570 - vendor-sys/illumos/dist/uts/common/fs/zfs vendor/illumos/dist/cmd/ztest X-SVN-Group: vendor-sys 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: 2.1.18 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: Tue, 17 Jun 2014 08:02:52 -0000 Author: delphij Date: Tue Jun 17 08:02:50 2014 New Revision: 267570 URL: http://svnweb.freebsd.org/changeset/base/267570 Log: 4756 metaslab_group_preload() could deadlock Reviewed by: Matthew Ahrens Reviewed by: Christopher Siden Reviewed by: Dan McDonald Reviewed by: Saso Kiselkov Approved by: Garrett D'Amore illumos/illumos-gate@30beaff42d8240ebf5386e8b7a14e3d137a1631f Modified: vendor-sys/illumos/dist/uts/common/fs/zfs/metaslab.c Changes in other areas also in this revision: Modified: vendor/illumos/dist/cmd/ztest/ztest.c Modified: vendor-sys/illumos/dist/uts/common/fs/zfs/metaslab.c ============================================================================== --- vendor-sys/illumos/dist/uts/common/fs/zfs/metaslab.c Tue Jun 17 07:58:53 2014 (r267569) +++ vendor-sys/illumos/dist/uts/common/fs/zfs/metaslab.c Tue Jun 17 08:02:50 2014 (r267570) @@ -1207,6 +1207,8 @@ metaslab_preload(void *arg) metaslab_t *msp = arg; spa_t *spa = msp->ms_group->mg_vd->vdev_spa; + ASSERT(!MUTEX_HELD(&msp->ms_group->mg_lock)); + mutex_enter(&msp->ms_lock); metaslab_load_wait(msp); if (!msp->ms_loaded) @@ -1231,19 +1233,36 @@ metaslab_group_preload(metaslab_group_t taskq_wait(mg->mg_taskq); return; } - mutex_enter(&mg->mg_lock); + mutex_enter(&mg->mg_lock); /* - * Prefetch the next potential metaslabs + * Load the next potential metaslabs */ - for (msp = avl_first(t); msp != NULL; msp = AVL_NEXT(t, msp)) { + msp = avl_first(t); + while (msp != NULL) { + metaslab_t *msp_next = AVL_NEXT(t, msp); /* If we have reached our preload limit then we're done */ if (++m > metaslab_preload_limit) break; + /* + * We must drop the metaslab group lock here to preserve + * lock ordering with the ms_lock (when grabbing both + * the mg_lock and the ms_lock, the ms_lock must be taken + * first). As a result, it is possible that the ordering + * of the metaslabs within the avl tree may change before + * we reacquire the lock. The metaslab cannot be removed from + * the tree while we're in syncing context so it is safe to + * drop the mg_lock here. If the metaslabs are reordered + * nothing will break -- we just may end up loading a + * less than optimal one. + */ + mutex_exit(&mg->mg_lock); VERIFY(taskq_dispatch(mg->mg_taskq, metaslab_preload, msp, TQ_SLEEP) != NULL); + mutex_enter(&mg->mg_lock); + msp = msp_next; } mutex_exit(&mg->mg_lock); }