Exemplo n.º 1
0
/*ARGSUSED*/
static kmem_cbrc_t
zfs_znode_move(void *buf, void *newbuf, size_t size, void *arg)
{
	znode_t *ozp = buf, *nzp = newbuf;
	zfsvfs_t *zfsvfs;
	vnode_t *vp;

	/*
	 * The znode is on the file system's list of known znodes if the vfs
	 * pointer is valid. We set the low bit of the vfs pointer when freeing
	 * the znode to invalidate it, and the memory patterns written by kmem
	 * (baddcafe and deadbeef) set at least one of the two low bits. A newly
	 * created znode sets the vfs pointer last of all to indicate that the
	 * znode is known and in a valid state to be moved by this function.
	 */
	zfsvfs = ozp->z_zfsvfs;
	if (!POINTER_IS_VALID(zfsvfs)) {
		ZNODE_STAT_ADD(znode_move_stats.zms_zfsvfs_invalid);
		return (KMEM_CBRC_DONT_KNOW);
	}

	/*
	 * Ensure that the filesystem is not unmounted during the move.
	 */
	if (zfs_enter(zfsvfs) != 0) {		/* ZFS_ENTER */
		ZNODE_STAT_ADD(znode_move_stats.zms_zfsvfs_unmounted);
		return (KMEM_CBRC_DONT_KNOW);
	}

	mutex_enter(&zfsvfs->z_znodes_lock);
	/*
	 * Recheck the vfs pointer in case the znode was removed just before
	 * acquiring the lock.
	 */
	if (zfsvfs != ozp->z_zfsvfs) {
		mutex_exit(&zfsvfs->z_znodes_lock);
		ZFS_EXIT(zfsvfs);
		ZNODE_STAT_ADD(znode_move_stats.zms_zfsvfs_recheck_invalid);
		return (KMEM_CBRC_DONT_KNOW);
	}

	/*
	 * At this point we know that as long as we hold z_znodes_lock, the
	 * znode cannot be freed and fields within the znode can be safely
	 * accessed. Now, prevent a race with zfs_zget().
	 */
	if (ZFS_OBJ_HOLD_TRYENTER(zfsvfs, ozp->z_id) == 0) {
		mutex_exit(&zfsvfs->z_znodes_lock);
		ZFS_EXIT(zfsvfs);
		ZNODE_STAT_ADD(znode_move_stats.zms_obj_held);
		return (KMEM_CBRC_LATER);
	}

	vp = ZTOV(ozp);
	if (mutex_tryenter(&vp->v_lock) == 0) {
		ZFS_OBJ_HOLD_EXIT(zfsvfs, ozp->z_id);
		mutex_exit(&zfsvfs->z_znodes_lock);
		ZFS_EXIT(zfsvfs);
		ZNODE_STAT_ADD(znode_move_stats.zms_vnode_locked);
		return (KMEM_CBRC_LATER);
	}

	/* Only move znodes that are referenced _only_ by the DNLC. */
	if (vp->v_count != 1 || !vn_in_dnlc(vp)) {
		mutex_exit(&vp->v_lock);
		ZFS_OBJ_HOLD_EXIT(zfsvfs, ozp->z_id);
		mutex_exit(&zfsvfs->z_znodes_lock);
		ZFS_EXIT(zfsvfs);
		ZNODE_STAT_ADD(znode_move_stats.zms_not_only_dnlc);
		return (KMEM_CBRC_LATER);
	}

	/*
	 * The znode is known and in a valid state to move. We're holding the
	 * locks needed to execute the critical section.
	 */
	zfs_znode_move_impl(ozp, nzp);
	mutex_exit(&vp->v_lock);
	ZFS_OBJ_HOLD_EXIT(zfsvfs, ozp->z_id);

	list_link_replace(&ozp->z_link_node, &nzp->z_link_node);
	mutex_exit(&zfsvfs->z_znodes_lock);
	ZFS_EXIT(zfsvfs);

	return (KMEM_CBRC_YES);
}
Exemplo n.º 2
0
/*ARGSUSED*/
static kmem_cbrc_t
zfs_znode_move(void *buf, void *newbuf, size_t size, void *arg)
{
	znode_t *ozp = buf, *nzp = newbuf;
	zfsvfs_t *zfsvfs;
	vnode_t *vp;

	/*
	 * The znode is on the file system's list of known znodes if the vfs
	 * pointer is valid. We set the low bit of the vfs pointer when freeing
	 * the znode to invalidate it, and the memory patterns written by kmem
	 * (baddcafe and deadbeef) set at least one of the two low bits. A newly
	 * created znode sets the vfs pointer last of all to indicate that the
	 * znode is known and in a valid state to be moved by this function.
	 */
	zfsvfs = ozp->z_zfsvfs;
	if (!POINTER_IS_VALID(zfsvfs)) {
		ZNODE_STAT_ADD(znode_move_stats.zms_zfsvfs_invalid);
		return (KMEM_CBRC_DONT_KNOW);
	}

	/*
	 * Close a small window in which it's possible that the filesystem could
	 * be unmounted and freed, and zfsvfs, though valid in the previous
	 * statement, could point to unrelated memory by the time we try to
	 * prevent the filesystem from being unmounted.
	 */
	rw_enter(&zfsvfs_lock, RW_WRITER);
	if (zfsvfs != ozp->z_zfsvfs) {
		rw_exit(&zfsvfs_lock);
		ZNODE_STAT_ADD(znode_move_stats.zms_zfsvfs_recheck1);
		return (KMEM_CBRC_DONT_KNOW);
	}

	/*
	 * If the znode is still valid, then so is the file system. We know that
	 * no valid file system can be freed while we hold zfsvfs_lock, so we
	 * can safely ensure that the filesystem is not and will not be
	 * unmounted. The next statement is equivalent to ZFS_ENTER().
	 */
	rrw_enter(&zfsvfs->z_teardown_lock, RW_READER, FTAG);
	if (zfsvfs->z_unmounted) {
		ZFS_EXIT(zfsvfs);
		rw_exit(&zfsvfs_lock);
		ZNODE_STAT_ADD(znode_move_stats.zms_zfsvfs_unmounted);
		return (KMEM_CBRC_DONT_KNOW);
	}
	rw_exit(&zfsvfs_lock);

	mutex_enter(&zfsvfs->z_znodes_lock);
	/*
	 * Recheck the vfs pointer in case the znode was removed just before
	 * acquiring the lock.
	 */
	if (zfsvfs != ozp->z_zfsvfs) {
		mutex_exit(&zfsvfs->z_znodes_lock);
		ZFS_EXIT(zfsvfs);
		ZNODE_STAT_ADD(znode_move_stats.zms_zfsvfs_recheck2);
		return (KMEM_CBRC_DONT_KNOW);
	}

	/*
	 * At this point we know that as long as we hold z_znodes_lock, the
	 * znode cannot be freed and fields within the znode can be safely
	 * accessed. Now, prevent a race with zfs_zget().
	 */
	if (ZFS_OBJ_HOLD_TRYENTER(zfsvfs, ozp->z_id) == 0) {
		mutex_exit(&zfsvfs->z_znodes_lock);
		ZFS_EXIT(zfsvfs);
		ZNODE_STAT_ADD(znode_move_stats.zms_obj_held);
		return (KMEM_CBRC_LATER);
	}

	vp = ZTOV(ozp);
	if (mutex_tryenter(&vp->v_lock) == 0) {
		ZFS_OBJ_HOLD_EXIT(zfsvfs, ozp->z_id);
		mutex_exit(&zfsvfs->z_znodes_lock);
		ZFS_EXIT(zfsvfs);
		ZNODE_STAT_ADD(znode_move_stats.zms_vnode_locked);
		return (KMEM_CBRC_LATER);
	}

	/* Only move znodes that are referenced _only_ by the DNLC. */
	if (vp->v_count != 1 || !vn_in_dnlc(vp)) {
		mutex_exit(&vp->v_lock);
		ZFS_OBJ_HOLD_EXIT(zfsvfs, ozp->z_id);
		mutex_exit(&zfsvfs->z_znodes_lock);
		ZFS_EXIT(zfsvfs);
		ZNODE_STAT_ADD(znode_move_stats.zms_not_only_dnlc);
		return (KMEM_CBRC_LATER);
	}

	/*
	 * The znode is known and in a valid state to move. We're holding the
	 * locks needed to execute the critical section.
	 */
	zfs_znode_move_impl(ozp, nzp);
	mutex_exit(&vp->v_lock);
	ZFS_OBJ_HOLD_EXIT(zfsvfs, ozp->z_id);

	list_link_replace(&ozp->z_link_node, &nzp->z_link_node);
	mutex_exit(&zfsvfs->z_znodes_lock);
	ZFS_EXIT(zfsvfs);

	return (KMEM_CBRC_YES);
}