pnode.c 15.1 KB
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560 561 562 563 564 565 566 567 568 569 570 571 572 573 574 575 576 577 578 579 580 581 582 583 584 585 586 587 588 589 590 591 592 593 594 595 596 597 598 599 600 601 602 603
// SPDX-License-Identifier: GPL-2.0-only
/*
 *  linux/fs/pnode.c
 *
 * (C) Copyright IBM Corporation 2005.
 *	Author : Ram Pai (linuxram@us.ibm.com)
 */
#include <linux/mnt_namespace.h>
#include <linux/mount.h>
#include <linux/fs.h>
#include <linux/nsproxy.h>
#include <uapi/linux/mount.h>
#include "internal.h"
#include "pnode.h"

/* return the next shared peer mount of @p */
static inline struct mount *next_peer(struct mount *p)
{
	return list_entry(p->mnt_share.next, struct mount, mnt_share);
}

static inline struct mount *first_slave(struct mount *p)
{
	return list_entry(p->mnt_slave_list.next, struct mount, mnt_slave);
}

static inline struct mount *last_slave(struct mount *p)
{
	return list_entry(p->mnt_slave_list.prev, struct mount, mnt_slave);
}

static inline struct mount *next_slave(struct mount *p)
{
	return list_entry(p->mnt_slave.next, struct mount, mnt_slave);
}

static struct mount *get_peer_under_root(struct mount *mnt,
					 struct mnt_namespace *ns,
					 const struct path *root)
{
	struct mount *m = mnt;

	do {
		/* Check the namespace first for optimization */
		if (m->mnt_ns == ns && is_path_reachable(m, m->mnt.mnt_root, root))
			return m;

		m = next_peer(m);
	} while (m != mnt);

	return NULL;
}

/*
 * Get ID of closest dominating peer group having a representative
 * under the given root.
 *
 * Caller must hold namespace_sem
 */
int get_dominating_id(struct mount *mnt, const struct path *root)
{
	struct mount *m;

	for (m = mnt->mnt_master; m != NULL; m = m->mnt_master) {
		struct mount *d = get_peer_under_root(m, mnt->mnt_ns, root);
		if (d)
			return d->mnt_group_id;
	}

	return 0;
}

static int do_make_slave(struct mount *mnt)
{
	struct mount *master, *slave_mnt;

	if (list_empty(&mnt->mnt_share)) {
		if (IS_MNT_SHARED(mnt)) {
			mnt_release_group_id(mnt);
			CLEAR_MNT_SHARED(mnt);
		}
		master = mnt->mnt_master;
		if (!master) {
			struct list_head *p = &mnt->mnt_slave_list;
			while (!list_empty(p)) {
				slave_mnt = list_first_entry(p,
						struct mount, mnt_slave);
				list_del_init(&slave_mnt->mnt_slave);
				slave_mnt->mnt_master = NULL;
			}
			return 0;
		}
	} else {
		struct mount *m;
		/*
		 * slave 'mnt' to a peer mount that has the
		 * same root dentry. If none is available then
		 * slave it to anything that is available.
		 */
		for (m = master = next_peer(mnt); m != mnt; m = next_peer(m)) {
			if (m->mnt.mnt_root == mnt->mnt.mnt_root) {
				master = m;
				break;
			}
		}
		list_del_init(&mnt->mnt_share);
		mnt->mnt_group_id = 0;
		CLEAR_MNT_SHARED(mnt);
	}
	list_for_each_entry(slave_mnt, &mnt->mnt_slave_list, mnt_slave)
		slave_mnt->mnt_master = master;
	list_move(&mnt->mnt_slave, &master->mnt_slave_list);
	list_splice(&mnt->mnt_slave_list, master->mnt_slave_list.prev);
	INIT_LIST_HEAD(&mnt->mnt_slave_list);
	mnt->mnt_master = master;
	return 0;
}

/*
 * vfsmount lock must be held for write
 */
void change_mnt_propagation(struct mount *mnt, int type)
{
	if (type == MS_SHARED) {
		set_mnt_shared(mnt);
		return;
	}
	do_make_slave(mnt);
	if (type != MS_SLAVE) {
		list_del_init(&mnt->mnt_slave);
		mnt->mnt_master = NULL;
		if (type == MS_UNBINDABLE)
			mnt->mnt.mnt_flags |= MNT_UNBINDABLE;
		else
			mnt->mnt.mnt_flags &= ~MNT_UNBINDABLE;
	}
}

/*
 * get the next mount in the propagation tree.
 * @m: the mount seen last
 * @origin: the original mount from where the tree walk initiated
 *
 * Note that peer groups form contiguous segments of slave lists.
 * We rely on that in get_source() to be able to find out if
 * vfsmount found while iterating with propagation_next() is
 * a peer of one we'd found earlier.
 */
static struct mount *propagation_next(struct mount *m,
					 struct mount *origin)
{
	/* are there any slaves of this mount? */
	if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
		return first_slave(m);

	while (1) {
		struct mount *master = m->mnt_master;

		if (master == origin->mnt_master) {
			struct mount *next = next_peer(m);
			return (next == origin) ? NULL : next;
		} else if (m->mnt_slave.next != &master->mnt_slave_list)
			return next_slave(m);

		/* back at master */
		m = master;
	}
}

static struct mount *skip_propagation_subtree(struct mount *m,
						struct mount *origin)
{
	/*
	 * Advance m such that propagation_next will not return
	 * the slaves of m.
	 */
	if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
		m = last_slave(m);

	return m;
}

static struct mount *next_group(struct mount *m, struct mount *origin)
{
	while (1) {
		while (1) {
			struct mount *next;
			if (!IS_MNT_NEW(m) && !list_empty(&m->mnt_slave_list))
				return first_slave(m);
			next = next_peer(m);
			if (m->mnt_group_id == origin->mnt_group_id) {
				if (next == origin)
					return NULL;
			} else if (m->mnt_slave.next != &next->mnt_slave)
				break;
			m = next;
		}
		/* m is the last peer */
		while (1) {
			struct mount *master = m->mnt_master;
			if (m->mnt_slave.next != &master->mnt_slave_list)
				return next_slave(m);
			m = next_peer(master);
			if (master->mnt_group_id == origin->mnt_group_id)
				break;
			if (master->mnt_slave.next == &m->mnt_slave)
				break;
			m = master;
		}
		if (m == origin)
			return NULL;
	}
}

/* all accesses are serialized by namespace_sem */
static struct mount *last_dest, *first_source, *last_source, *dest_master;
static struct mountpoint *mp;
static struct hlist_head *list;

static inline bool peers(struct mount *m1, struct mount *m2)
{
	return m1->mnt_group_id == m2->mnt_group_id && m1->mnt_group_id;
}

static int propagate_one(struct mount *m)
{
	struct mount *child;
	int type;
	/* skip ones added by this propagate_mnt() */
	if (IS_MNT_NEW(m))
		return 0;
	/* skip if mountpoint isn't covered by it */
	if (!is_subdir(mp->m_dentry, m->mnt.mnt_root))
		return 0;
	if (peers(m, last_dest)) {
		type = CL_MAKE_SHARED;
	} else {
		struct mount *n, *p;
		bool done;
		for (n = m; ; n = p) {
			p = n->mnt_master;
			if (p == dest_master || IS_MNT_MARKED(p))
				break;
		}
		do {
			struct mount *parent = last_source->mnt_parent;
			if (last_source == first_source)
				break;
			done = parent->mnt_master == p;
			if (done && peers(n, parent))
				break;
			last_source = last_source->mnt_master;
		} while (!done);

		type = CL_SLAVE;
		/* beginning of peer group among the slaves? */
		if (IS_MNT_SHARED(m))
			type |= CL_MAKE_SHARED;
	}
		
	child = copy_tree(last_source, last_source->mnt.mnt_root, type);
	if (IS_ERR(child))
		return PTR_ERR(child);
	mnt_set_mountpoint(m, mp, child);
	last_dest = m;
	last_source = child;
	if (m->mnt_master != dest_master) {
		read_seqlock_excl(&mount_lock);
		SET_MNT_MARK(m->mnt_master);
		read_sequnlock_excl(&mount_lock);
	}
	hlist_add_head(&child->mnt_hash, list);
	return count_mounts(m->mnt_ns, child);
}

/*
 * mount 'source_mnt' under the destination 'dest_mnt' at
 * dentry 'dest_dentry'. And propagate that mount to
 * all the peer and slave mounts of 'dest_mnt'.
 * Link all the new mounts into a propagation tree headed at
 * source_mnt. Also link all the new mounts using ->mnt_list
 * headed at source_mnt's ->mnt_list
 *
 * @dest_mnt: destination mount.
 * @dest_dentry: destination dentry.
 * @source_mnt: source mount.
 * @tree_list : list of heads of trees to be attached.
 */
int propagate_mnt(struct mount *dest_mnt, struct mountpoint *dest_mp,
		    struct mount *source_mnt, struct hlist_head *tree_list)
{
	struct mount *m, *n;
	int ret = 0;

	/*
	 * we don't want to bother passing tons of arguments to
	 * propagate_one(); everything is serialized by namespace_sem,
	 * so globals will do just fine.
	 */
	last_dest = dest_mnt;
	first_source = source_mnt;
	last_source = source_mnt;
	mp = dest_mp;
	list = tree_list;
	dest_master = dest_mnt->mnt_master;

	/* all peers of dest_mnt, except dest_mnt itself */
	for (n = next_peer(dest_mnt); n != dest_mnt; n = next_peer(n)) {
		ret = propagate_one(n);
		if (ret)
			goto out;
	}

	/* all slave groups */
	for (m = next_group(dest_mnt, dest_mnt); m;
			m = next_group(m, dest_mnt)) {
		/* everything in that slave group */
		n = m;
		do {
			ret = propagate_one(n);
			if (ret)
				goto out;
			n = next_peer(n);
		} while (n != m);
	}
out:
	read_seqlock_excl(&mount_lock);
	hlist_for_each_entry(n, tree_list, mnt_hash) {
		m = n->mnt_parent;
		if (m->mnt_master != dest_mnt->mnt_master)
			CLEAR_MNT_MARK(m->mnt_master);
	}
	read_sequnlock_excl(&mount_lock);
	return ret;
}

static struct mount *find_topper(struct mount *mnt)
{
	/* If there is exactly one mount covering mnt completely return it. */
	struct mount *child;

	if (!list_is_singular(&mnt->mnt_mounts))
		return NULL;

	child = list_first_entry(&mnt->mnt_mounts, struct mount, mnt_child);
	if (child->mnt_mountpoint != mnt->mnt.mnt_root)
		return NULL;

	return child;
}

/*
 * return true if the refcount is greater than count
 */
static inline int do_refcount_check(struct mount *mnt, int count)
{
	return mnt_get_count(mnt) > count;
}

/*
 * check if the mount 'mnt' can be unmounted successfully.
 * @mnt: the mount to be checked for unmount
 * NOTE: unmounting 'mnt' would naturally propagate to all
 * other mounts its parent propagates to.
 * Check if any of these mounts that **do not have submounts**
 * have more references than 'refcnt'. If so return busy.
 *
 * vfsmount lock must be held for write
 */
int propagate_mount_busy(struct mount *mnt, int refcnt)
{
	struct mount *m, *child, *topper;
	struct mount *parent = mnt->mnt_parent;

	if (mnt == parent)
		return do_refcount_check(mnt, refcnt);

	/*
	 * quickly check if the current mount can be unmounted.
	 * If not, we don't have to go checking for all other
	 * mounts
	 */
	if (!list_empty(&mnt->mnt_mounts) || do_refcount_check(mnt, refcnt))
		return 1;

	for (m = propagation_next(parent, parent); m;
	     		m = propagation_next(m, parent)) {
		int count = 1;
		child = __lookup_mnt(&m->mnt, mnt->mnt_mountpoint);
		if (!child)
			continue;

		/* Is there exactly one mount on the child that covers
		 * it completely whose reference should be ignored?
		 */
		topper = find_topper(child);
		if (topper)
			count += 1;
		else if (!list_empty(&child->mnt_mounts))
			continue;

		if (do_refcount_check(child, count))
			return 1;
	}
	return 0;
}

/*
 * Clear MNT_LOCKED when it can be shown to be safe.
 *
 * mount_lock lock must be held for write
 */
void propagate_mount_unlock(struct mount *mnt)
{
	struct mount *parent = mnt->mnt_parent;
	struct mount *m, *child;

	BUG_ON(parent == mnt);

	for (m = propagation_next(parent, parent); m;
			m = propagation_next(m, parent)) {
		child = __lookup_mnt(&m->mnt, mnt->mnt_mountpoint);
		if (child)
			child->mnt.mnt_flags &= ~MNT_LOCKED;
	}
}

static void umount_one(struct mount *mnt, struct list_head *to_umount)
{
	CLEAR_MNT_MARK(mnt);
	mnt->mnt.mnt_flags |= MNT_UMOUNT;
	list_del_init(&mnt->mnt_child);
	list_del_init(&mnt->mnt_umounting);
	list_move_tail(&mnt->mnt_list, to_umount);
}

/*
 * NOTE: unmounting 'mnt' naturally propagates to all other mounts its
 * parent propagates to.
 */
static bool __propagate_umount(struct mount *mnt,
			       struct list_head *to_umount,
			       struct list_head *to_restore)
{
	bool progress = false;
	struct mount *child;

	/*
	 * The state of the parent won't change if this mount is
	 * already unmounted or marked as without children.
	 */
	if (mnt->mnt.mnt_flags & (MNT_UMOUNT | MNT_MARKED))
		goto out;

	/* Verify topper is the only grandchild that has not been
	 * speculatively unmounted.
	 */
	list_for_each_entry(child, &mnt->mnt_mounts, mnt_child) {
		if (child->mnt_mountpoint == mnt->mnt.mnt_root)
			continue;
		if (!list_empty(&child->mnt_umounting) && IS_MNT_MARKED(child))
			continue;
		/* Found a mounted child */
		goto children;
	}

	/* Mark mounts that can be unmounted if not locked */
	SET_MNT_MARK(mnt);
	progress = true;

	/* If a mount is without children and not locked umount it. */
	if (!IS_MNT_LOCKED(mnt)) {
		umount_one(mnt, to_umount);
	} else {
children:
		list_move_tail(&mnt->mnt_umounting, to_restore);
	}
out:
	return progress;
}

static void umount_list(struct list_head *to_umount,
			struct list_head *to_restore)
{
	struct mount *mnt, *child, *tmp;
	list_for_each_entry(mnt, to_umount, mnt_list) {
		list_for_each_entry_safe(child, tmp, &mnt->mnt_mounts, mnt_child) {
			/* topper? */
			if (child->mnt_mountpoint == mnt->mnt.mnt_root)
				list_move_tail(&child->mnt_umounting, to_restore);
			else
				umount_one(child, to_umount);
		}
	}
}

static void restore_mounts(struct list_head *to_restore)
{
	/* Restore mounts to a clean working state */
	while (!list_empty(to_restore)) {
		struct mount *mnt, *parent;
		struct mountpoint *mp;

		mnt = list_first_entry(to_restore, struct mount, mnt_umounting);
		CLEAR_MNT_MARK(mnt);
		list_del_init(&mnt->mnt_umounting);

		/* Should this mount be reparented? */
		mp = mnt->mnt_mp;
		parent = mnt->mnt_parent;
		while (parent->mnt.mnt_flags & MNT_UMOUNT) {
			mp = parent->mnt_mp;
			parent = parent->mnt_parent;
		}
		if (parent != mnt->mnt_parent)
			mnt_change_mountpoint(parent, mp, mnt);
	}
}

static void cleanup_umount_visitations(struct list_head *visited)
{
	while (!list_empty(visited)) {
		struct mount *mnt =
			list_first_entry(visited, struct mount, mnt_umounting);
		list_del_init(&mnt->mnt_umounting);
	}
}

/*
 * collect all mounts that receive propagation from the mount in @list,
 * and return these additional mounts in the same list.
 * @list: the list of mounts to be unmounted.
 *
 * vfsmount lock must be held for write
 */
int propagate_umount(struct list_head *list)
{
	struct mount *mnt;
	LIST_HEAD(to_restore);
	LIST_HEAD(to_umount);
	LIST_HEAD(visited);

	/* Find candidates for unmounting */
	list_for_each_entry_reverse(mnt, list, mnt_list) {
		struct mount *parent = mnt->mnt_parent;
		struct mount *m;

		/*
		 * If this mount has already been visited it is known that it's
		 * entire peer group and all of their slaves in the propagation
		 * tree for the mountpoint has already been visited and there is
		 * no need to visit them again.
		 */
		if (!list_empty(&mnt->mnt_umounting))
			continue;

		list_add_tail(&mnt->mnt_umounting, &visited);
		for (m = propagation_next(parent, parent); m;
		     m = propagation_next(m, parent)) {
			struct mount *child = __lookup_mnt(&m->mnt,
							   mnt->mnt_mountpoint);
			if (!child)
				continue;

			if (!list_empty(&child->mnt_umounting)) {
				/*
				 * If the child has already been visited it is
				 * know that it's entire peer group and all of
				 * their slaves in the propgation tree for the
				 * mountpoint has already been visited and there
				 * is no need to visit this subtree again.
				 */
				m = skip_propagation_subtree(m, parent);
				continue;
			} else if (child->mnt.mnt_flags & MNT_UMOUNT) {
				/*
				 * We have come accross an partially unmounted
				 * mount in list that has not been visited yet.
				 * Remember it has been visited and continue
				 * about our merry way.
				 */
				list_add_tail(&child->mnt_umounting, &visited);
				continue;
			}

			/* Check the child and parents while progress is made */
			while (__propagate_umount(child,
						  &to_umount, &to_restore)) {
				/* Is the parent a umount candidate? */
				child = child->mnt_parent;
				if (list_empty(&child->mnt_umounting))
					break;
			}
		}
	}

	umount_list(&to_umount, &to_restore);
	restore_mounts(&to_restore);
	cleanup_umount_visitations(&visited);
	list_splice_tail(&to_umount, list);

	return 0;
}