From owner-svn-src-all@freebsd.org Sun Nov 13 21:49:52 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 9F9FFC3FCF2; Sun, 13 Nov 2016 21:49:52 +0000 (UTC) (envelope-from kib@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 6BF73136F; Sun, 13 Nov 2016 21:49:52 +0000 (UTC) (envelope-from kib@FreeBSD.org) Received: from repo.freebsd.org ([127.0.1.37]) by repo.freebsd.org (8.15.2/8.15.2) with ESMTP id uADLnpNl016428; Sun, 13 Nov 2016 21:49:51 GMT (envelope-from kib@FreeBSD.org) Received: (from kib@localhost) by repo.freebsd.org (8.15.2/8.15.2/Submit) id uADLnpac016426; Sun, 13 Nov 2016 21:49:51 GMT (envelope-from kib@FreeBSD.org) Message-Id: <201611132149.uADLnpac016426@repo.freebsd.org> X-Authentication-Warning: repo.freebsd.org: kib set sender to kib@FreeBSD.org using -f From: Konstantin Belousov Date: Sun, 13 Nov 2016 21:49:51 +0000 (UTC) To: src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org Subject: svn commit: r308618 - in head/sys: kern ufs/ffs 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: 2.1.23 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: Sun, 13 Nov 2016 21:49:52 -0000 Author: kib Date: Sun Nov 13 21:49:51 2016 New Revision: 308618 URL: https://svnweb.freebsd.org/changeset/base/308618 Log: Provide simple mutual exclusion between mount point update and unmount. Currently mount update keeps vfs_busy(9) reference on the mount point during MNT_UPDATE VFS_MOUNT() vfsops call. This already provides the exclusion, but is problematic for filesystems which need to perform namei(9) during VFS_MOUNT(MNT_UPDATE) operations, e.g. to refresh mnt_from path, because namei(9) must not be called while the vfs_busy(9) reference is owned. Check for MNT_UPDATE flag before setting MNTK_UNMOUNT, and for MNTK_UNMOUNT before entering innards of vfs_domount_update(), failing syscalls with EBUSY if conflict is detected. Keep vfs_busy(9) reference around VFS_MOUNT(MNT_UPDATE) calls still to not change VFS KPI. In the update path in ffs_mount(), drop vfs_busy() reference around namei(), which is now safe due to unmount never executing in parallel with VFS_MOUNT(MNT_UPDATE), and which avoids the deadlock. Reported and tested by: pho Sponsored by: The FreeBSD Foundation MFC after: 2 weeks Modified: head/sys/kern/vfs_mount.c head/sys/ufs/ffs/ffs_vfsops.c Modified: head/sys/kern/vfs_mount.c ============================================================================== --- head/sys/kern/vfs_mount.c Sun Nov 13 21:39:55 2016 (r308617) +++ head/sys/kern/vfs_mount.c Sun Nov 13 21:49:51 2016 (r308618) @@ -940,6 +940,11 @@ vfs_domount_update( VOP_UNLOCK(vp, 0); MNT_ILOCK(mp); + if ((mp->mnt_kern_flag & MNTK_UNMOUNT) != 0) { + MNT_IUNLOCK(mp); + error = EBUSY; + goto end; + } mp->mnt_flag &= ~MNT_UPDATEMASK; mp->mnt_flag |= fsflags & (MNT_RELOAD | MNT_FORCE | MNT_UPDATE | MNT_SNAPSHOT | MNT_ROOTFS | MNT_UPDATEMASK | MNT_RDONLY); @@ -1299,6 +1304,7 @@ dounmount(struct mount *mp, int flags, s vn_start_write(NULL, &mp, V_WAIT | V_MNTREF); MNT_ILOCK(mp); if ((mp->mnt_kern_flag & MNTK_UNMOUNT) != 0 || + (mp->mnt_flag & MNT_UPDATE) != 0 || !TAILQ_EMPTY(&mp->mnt_uppers)) { dounmount_cleanup(mp, coveredvp, 0); return (EBUSY); Modified: head/sys/ufs/ffs/ffs_vfsops.c ============================================================================== --- head/sys/ufs/ffs/ffs_vfsops.c Sun Nov 13 21:39:55 2016 (r308617) +++ head/sys/ufs/ffs/ffs_vfsops.c Sun Nov 13 21:49:51 2016 (r308618) @@ -147,7 +147,7 @@ ffs_mount(struct mount *mp) struct ufsmount *ump = NULL; struct fs *fs; pid_t fsckpid = 0; - int error, flags; + int error, error1, flags; uint64_t mntorflags; accmode_t accmode; struct nameidata ndp; @@ -453,6 +453,11 @@ ffs_mount(struct mount *mp) */ if (mp->mnt_flag & MNT_SNAPSHOT) return (ffs_snapshot(mp, fspec)); + + /* + * Must not call namei() while owning busy ref. + */ + vfs_unbusy(mp); } /* @@ -460,7 +465,18 @@ ffs_mount(struct mount *mp) * and verify that it refers to a sensible disk device. */ NDINIT(&ndp, LOOKUP, FOLLOW | LOCKLEAF, UIO_SYSSPACE, fspec, td); - if ((error = namei(&ndp)) != 0) + error = namei(&ndp); + if ((mp->mnt_flag & MNT_UPDATE) != 0) { + /* + * Unmount does not start if MNT_UPDATE is set. Mount + * update busies mp before setting MNT_UPDATE. We + * must be able to retain our busy ref succesfully, + * without sleep. + */ + error1 = vfs_busy(mp, MBF_NOWAIT); + MPASS(error1 == 0); + } + if (error != 0) return (error); NDFREE(&ndp, NDF_ONLY_PNBUF); devvp = ndp.ni_vp;