From owner-svn-src-all@freebsd.org Mon May 16 15:03:54 2016 Return-Path: Delivered-To: svn-src-all@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id 293AEB3D549; Mon, 16 May 2016 15:03:54 +0000 (UTC) (envelope-from avg@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 mx1.freebsd.org (Postfix) with ESMTPS id D44D71FAE; Mon, 16 May 2016 15:03:53 +0000 (UTC) (envelope-from avg@FreeBSD.org) Received: from repo.freebsd.org ([127.0.1.37]) by repo.freebsd.org (8.15.2/8.15.2) with ESMTP id u4GF3r4e020857; Mon, 16 May 2016 15:03:53 GMT (envelope-from avg@FreeBSD.org) Received: (from avg@localhost) by repo.freebsd.org (8.15.2/8.15.2/Submit) id u4GF3rRa020856; Mon, 16 May 2016 15:03:53 GMT (envelope-from avg@FreeBSD.org) Message-Id: <201605161503.u4GF3rRa020856@repo.freebsd.org> X-Authentication-Warning: repo.freebsd.org: avg set sender to avg@FreeBSD.org using -f From: Andriy Gapon Date: Mon, 16 May 2016 15:03:53 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r299945 - head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs X-SVN-Group: head 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: 2.1.22 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: Mon, 16 May 2016 15:03:54 -0000 Author: avg Date: Mon May 16 15:03:52 2016 New Revision: 299945 URL: https://svnweb.freebsd.org/changeset/base/299945 Log: avoid deadlock between zfsctl_snapdir_lookup and zfsctl_snapshot_reclaim The former acquired a snap vnode lock while holding sd_lock while the latter does the opposite. The solution is drop sd_lock before acquiring the vnode lock. That should be okay as we are still holding a lock on the 'snapshot' directory in the exclusive mode. That lock ensures that there are no concurrent lookups in the directory and thus no concurrent mount attempts. But now we have to account for the possibility that the snap vnode might get reclaim after we drop sd_lock and before we can get the node lock. So, check for that case and retry. MFC after: 5 weeks Modified: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_ctldir.c Modified: head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_ctldir.c ============================================================================== --- head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_ctldir.c Mon May 16 14:07:43 2016 (r299944) +++ head/sys/cddl/contrib/opensolaris/uts/common/fs/zfs/zfs_ctldir.c Mon May 16 15:03:52 2016 (r299945) @@ -1011,6 +1011,7 @@ zfsctl_snapdir_lookup(ap) #endif } +relookup: mutex_enter(&sdp->sd_lock); search.se_name = (char *)nm; if ((sep = avl_find(&sdp->sd_snaps, &search, &where)) != NULL) { @@ -1085,7 +1086,16 @@ domount: (void) snprintf(mountpoint, mountpoint_len, "%s/" ZFS_CTLDIR_NAME "/snapshot/%s", dvp->v_vfsp->mnt_stat.f_mntonname, nm); - VERIFY0(vn_lock(*vpp, LK_EXCLUSIVE)); + mutex_exit(&sdp->sd_lock); + + /* + * The vnode may get reclaimed between dropping sd_lock and + * getting the vnode lock. + * */ + err = vn_lock(*vpp, LK_EXCLUSIVE); + if (err == ENOENT) + goto relookup; + VERIFY0(err); err = mount_snapshot(curthread, vpp, "zfs", mountpoint, snapname, 0); kmem_free(mountpoint, mountpoint_len); if (err == 0) { @@ -1100,7 +1110,6 @@ domount: VTOZ(*vpp)->z_zfsvfs->z_parent = zfsvfs; (*vpp)->v_flag &= ~VROOT; } - mutex_exit(&sdp->sd_lock); ZFS_EXIT(zfsvfs); #ifdef illumos