1// SPDX-License-Identifier: GPL-2.0-or-later
   2/*
   3 *  Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
   4 */
   5
   6/*
   7 * fsnotify inode mark locking/lifetime/and refcnting
   8 *
   9 * REFCNT:
  10 * The group->recnt and mark->refcnt tell how many "things" in the kernel
  11 * currently are referencing the objects. Both kind of objects typically will
  12 * live inside the kernel with a refcnt of 2, one for its creation and one for
  13 * the reference a group and a mark hold to each other.
  14 * If you are holding the appropriate locks, you can take a reference and the
  15 * object itself is guaranteed to survive until the reference is dropped.
  16 *
  17 * LOCKING:
  18 * There are 3 locks involved with fsnotify inode marks and they MUST be taken
  19 * in order as follows:
  20 *
  21 * group->mark_mutex
  22 * mark->lock
  23 * mark->connector->lock
  24 *
  25 * group->mark_mutex protects the marks_list anchored inside a given group and
  26 * each mark is hooked via the g_list.  It also protects the groups private
  27 * data (i.e group limits).
  28
  29 * mark->lock protects the marks attributes like its masks and flags.
  30 * Furthermore it protects the access to a reference of the group that the mark
  31 * is assigned to as well as the access to a reference of the inode/vfsmount
  32 * that is being watched by the mark.
  33 *
  34 * mark->connector->lock protects the list of marks anchored inside an
  35 * inode / vfsmount and each mark is hooked via the i_list.
  36 *
  37 * A list of notification marks relating to inode / mnt is contained in
  38 * fsnotify_mark_connector. That structure is alive as long as there are any
  39 * marks in the list and is also protected by fsnotify_mark_srcu. A mark gets
  40 * detached from fsnotify_mark_connector when last reference to the mark is
  41 * dropped.  Thus having mark reference is enough to protect mark->connector
  42 * pointer and to make sure fsnotify_mark_connector cannot disappear. Also
  43 * because we remove mark from g_list before dropping mark reference associated
  44 * with that, any mark found through g_list is guaranteed to have
  45 * mark->connector set until we drop group->mark_mutex.
  46 *
  47 * LIFETIME:
  48 * Inode marks survive between when they are added to an inode and when their
  49 * refcnt==0. Marks are also protected by fsnotify_mark_srcu.
  50 *
  51 * The inode mark can be cleared for a number of different reasons including:
  52 * - The inode is unlinked for the last time.  (fsnotify_inode_remove)
  53 * - The inode is being evicted from cache. (fsnotify_inode_delete)
  54 * - The fs the inode is on is unmounted.  (fsnotify_inode_delete/fsnotify_unmount_inodes)
  55 * - Something explicitly requests that it be removed.  (fsnotify_destroy_mark)
  56 * - The fsnotify_group associated with the mark is going away and all such marks
  57 *   need to be cleaned up. (fsnotify_clear_marks_by_group)
  58 *
  59 * This has the very interesting property of being able to run concurrently with
  60 * any (or all) other directions.
  61 */
  62
  63#include <linux/fs.h>
  64#include <linux/init.h>
  65#include <linux/kernel.h>
  66#include <linux/kthread.h>
  67#include <linux/module.h>
  68#include <linux/mutex.h>
  69#include <linux/slab.h>
  70#include <linux/spinlock.h>
  71#include <linux/srcu.h>
  72#include <linux/ratelimit.h>
  73
  74#include <linux/atomic.h>
  75
  76#include <linux/fsnotify_backend.h>
  77#include "fsnotify.h"
  78
  79#define FSNOTIFY_REAPER_DELAY	(1)	/* 1 jiffy */
  80
  81struct srcu_struct fsnotify_mark_srcu;
  82struct kmem_cache *fsnotify_mark_connector_cachep;
  83
  84static DEFINE_SPINLOCK(destroy_lock);
  85static LIST_HEAD(destroy_list);
  86static struct fsnotify_mark_connector *connector_destroy_list;
  87
  88static void fsnotify_mark_destroy_workfn(struct work_struct *work);
  89static DECLARE_DELAYED_WORK(reaper_work, fsnotify_mark_destroy_workfn);
  90
  91static void fsnotify_connector_destroy_workfn(struct work_struct *work);
  92static DECLARE_WORK(connector_reaper_work, fsnotify_connector_destroy_workfn);
  93
  94void fsnotify_get_mark(struct fsnotify_mark *mark)
  95{
  96	WARN_ON_ONCE(!refcount_read(&mark->refcnt));
  97	refcount_inc(&mark->refcnt);
  98}
  99
 100static fsnotify_connp_t *fsnotify_object_connp(void *obj,
 101				enum fsnotify_obj_type obj_type)
 102{
 103	switch (obj_type) {
 104	case FSNOTIFY_OBJ_TYPE_INODE:
 105		return &((struct inode *)obj)->i_fsnotify_marks;
 106	case FSNOTIFY_OBJ_TYPE_VFSMOUNT:
 107		return &real_mount(obj)->mnt_fsnotify_marks;
 108	case FSNOTIFY_OBJ_TYPE_SB:
 109		return fsnotify_sb_marks(obj);
 110	default:
 111		return NULL;
 112	}
 113}
 114
 115static __u32 *fsnotify_conn_mask_p(struct fsnotify_mark_connector *conn)
 116{
 117	if (conn->type == FSNOTIFY_OBJ_TYPE_INODE)
 118		return &fsnotify_conn_inode(conn)->i_fsnotify_mask;
 119	else if (conn->type == FSNOTIFY_OBJ_TYPE_VFSMOUNT)
 120		return &fsnotify_conn_mount(conn)->mnt_fsnotify_mask;
 121	else if (conn->type == FSNOTIFY_OBJ_TYPE_SB)
 122		return &fsnotify_conn_sb(conn)->s_fsnotify_mask;
 123	return NULL;
 124}
 125
 126__u32 fsnotify_conn_mask(struct fsnotify_mark_connector *conn)
 127{
 128	if (WARN_ON(!fsnotify_valid_obj_type(conn->type)))
 129		return 0;
 130
 131	return READ_ONCE(*fsnotify_conn_mask_p(conn));
 132}
 133
 134static void fsnotify_get_sb_watched_objects(struct super_block *sb)
 135{
 136	atomic_long_inc(fsnotify_sb_watched_objects(sb));
 137}
 138
 139static void fsnotify_put_sb_watched_objects(struct super_block *sb)
 140{
 141	atomic_long_t *watched_objects = fsnotify_sb_watched_objects(sb);
 142
 143	/* the superblock can go away after this decrement */
 144	if (atomic_long_dec_and_test(watched_objects))
 145		wake_up_var(watched_objects);
 146}
 147
 148static void fsnotify_get_inode_ref(struct inode *inode)
 149{
 150	ihold(inode);
 151	fsnotify_get_sb_watched_objects(inode->i_sb);
 152}
 153
 154static void fsnotify_put_inode_ref(struct inode *inode)
 155{
 156	/* read ->i_sb before the inode can go away */
 157	struct super_block *sb = inode->i_sb;
 158
 159	iput(inode);
 160	fsnotify_put_sb_watched_objects(sb);
 161}
 162
 163/*
 164 * Grab or drop watched objects reference depending on whether the connector
 165 * is attached and has any marks attached.
 166 */
 167static void fsnotify_update_sb_watchers(struct super_block *sb,
 168					struct fsnotify_mark_connector *conn)
 169{
 170	struct fsnotify_sb_info *sbinfo = fsnotify_sb_info(sb);
 171	bool is_watched = conn->flags & FSNOTIFY_CONN_FLAG_IS_WATCHED;
 172	struct fsnotify_mark *first_mark = NULL;
 173	unsigned int highest_prio = 0;
 174
 175	if (conn->obj)
 176		first_mark = hlist_entry_safe(conn->list.first,
 177					      struct fsnotify_mark, obj_list);
 178	if (first_mark)
 179		highest_prio = first_mark->group->priority;
 180	if (WARN_ON(highest_prio >= __FSNOTIFY_PRIO_NUM))
 181		highest_prio = 0;
 182
 183	/*
 184	 * If the highest priority of group watching this object is prio,
 185	 * then watched object has a reference on counters [0..prio].
 186	 * Update priority >= 1 watched objects counters.
 187	 */
 188	for (unsigned int p = conn->prio + 1; p <= highest_prio; p++)
 189		atomic_long_inc(&sbinfo->watched_objects[p]);
 190	for (unsigned int p = conn->prio; p > highest_prio; p--)
 191		atomic_long_dec(&sbinfo->watched_objects[p]);
 192	conn->prio = highest_prio;
 193
 194	/* Update priority >= 0 (a.k.a total) watched objects counter */
 195	BUILD_BUG_ON(FSNOTIFY_PRIO_NORMAL != 0);
 196	if (first_mark && !is_watched) {
 197		conn->flags |= FSNOTIFY_CONN_FLAG_IS_WATCHED;
 198		fsnotify_get_sb_watched_objects(sb);
 199	} else if (!first_mark && is_watched) {
 200		conn->flags &= ~FSNOTIFY_CONN_FLAG_IS_WATCHED;
 201		fsnotify_put_sb_watched_objects(sb);
 202	}
 203}
 204
 205/*
 206 * Grab or drop inode reference for the connector if needed.
 207 *
 208 * When it's time to drop the reference, we only clear the HAS_IREF flag and
 209 * return the inode object. fsnotify_drop_object() will be resonsible for doing
 210 * iput() outside of spinlocks. This happens when last mark that wanted iref is
 211 * detached.
 212 */
 213static struct inode *fsnotify_update_iref(struct fsnotify_mark_connector *conn,
 214					  bool want_iref)
 215{
 216	bool has_iref = conn->flags & FSNOTIFY_CONN_FLAG_HAS_IREF;
 217	struct inode *inode = NULL;
 218
 219	if (conn->type != FSNOTIFY_OBJ_TYPE_INODE ||
 220	    want_iref == has_iref)
 221		return NULL;
 222
 223	if (want_iref) {
 224		/* Pin inode if any mark wants inode refcount held */
 225		fsnotify_get_inode_ref(fsnotify_conn_inode(conn));
 226		conn->flags |= FSNOTIFY_CONN_FLAG_HAS_IREF;
 227	} else {
 228		/* Unpin inode after detach of last mark that wanted iref */
 229		inode = fsnotify_conn_inode(conn);
 230		conn->flags &= ~FSNOTIFY_CONN_FLAG_HAS_IREF;
 231	}
 232
 233	return inode;
 234}
 235
 236static void *__fsnotify_recalc_mask(struct fsnotify_mark_connector *conn)
 237{
 238	u32 new_mask = 0;
 239	bool want_iref = false;
 240	struct fsnotify_mark *mark;
 241
 242	assert_spin_locked(&conn->lock);
 243	/* We can get detached connector here when inode is getting unlinked. */
 244	if (!fsnotify_valid_obj_type(conn->type))
 245		return NULL;
 246	hlist_for_each_entry(mark, &conn->list, obj_list) {
 247		if (!(mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED))
 248			continue;
 249		new_mask |= fsnotify_calc_mask(mark);
 250		if (conn->type == FSNOTIFY_OBJ_TYPE_INODE &&
 251		    !(mark->flags & FSNOTIFY_MARK_FLAG_NO_IREF))
 252			want_iref = true;
 253	}
 254	/*
 255	 * We use WRITE_ONCE() to prevent silly compiler optimizations from
 256	 * confusing readers not holding conn->lock with partial updates.
 257	 */
 258	WRITE_ONCE(*fsnotify_conn_mask_p(conn), new_mask);
 259
 260	return fsnotify_update_iref(conn, want_iref);
 261}
 262
 263static bool fsnotify_conn_watches_children(
 264					struct fsnotify_mark_connector *conn)
 265{
 266	if (conn->type != FSNOTIFY_OBJ_TYPE_INODE)
 267		return false;
 268
 269	return fsnotify_inode_watches_children(fsnotify_conn_inode(conn));
 270}
 271
 272static void fsnotify_conn_set_children_dentry_flags(
 273					struct fsnotify_mark_connector *conn)
 274{
 275	if (conn->type != FSNOTIFY_OBJ_TYPE_INODE)
 276		return;
 277
 278	fsnotify_set_children_dentry_flags(fsnotify_conn_inode(conn));
 279}
 280
 281/*
 282 * Calculate mask of events for a list of marks. The caller must make sure
 283 * connector and connector->obj cannot disappear under us.  Callers achieve
 284 * this by holding a mark->lock or mark->group->mark_mutex for a mark on this
 285 * list.
 286 */
 287void fsnotify_recalc_mask(struct fsnotify_mark_connector *conn)
 288{
 289	bool update_children;
 290
 291	if (!conn)
 292		return;
 293
 294	spin_lock(&conn->lock);
 295	update_children = !fsnotify_conn_watches_children(conn);
 296	__fsnotify_recalc_mask(conn);
 297	update_children &= fsnotify_conn_watches_children(conn);
 298	spin_unlock(&conn->lock);
 299	/*
 300	 * Set children's PARENT_WATCHED flags only if parent started watching.
 301	 * When parent stops watching, we clear false positive PARENT_WATCHED
 302	 * flags lazily in __fsnotify_parent().
 303	 */
 304	if (update_children)
 305		fsnotify_conn_set_children_dentry_flags(conn);
 306}
 307
 308/* Free all connectors queued for freeing once SRCU period ends */
 309static void fsnotify_connector_destroy_workfn(struct work_struct *work)
 310{
 311	struct fsnotify_mark_connector *conn, *free;
 312
 313	spin_lock(&destroy_lock);
 314	conn = connector_destroy_list;
 315	connector_destroy_list = NULL;
 316	spin_unlock(&destroy_lock);
 317
 318	synchronize_srcu(&fsnotify_mark_srcu);
 319	while (conn) {
 320		free = conn;
 321		conn = conn->destroy_next;
 322		kmem_cache_free(fsnotify_mark_connector_cachep, free);
 323	}
 324}
 325
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 326static void *fsnotify_detach_connector_from_object(
 327					struct fsnotify_mark_connector *conn,
 328					unsigned int *type)
 329{
 330	fsnotify_connp_t *connp = fsnotify_object_connp(conn->obj, conn->type);
 331	struct super_block *sb = fsnotify_connector_sb(conn);
 332	struct inode *inode = NULL;
 333
 334	*type = conn->type;
 335	if (conn->type == FSNOTIFY_OBJ_TYPE_DETACHED)
 336		return NULL;
 337
 338	if (conn->type == FSNOTIFY_OBJ_TYPE_INODE) {
 339		inode = fsnotify_conn_inode(conn);
 340		inode->i_fsnotify_mask = 0;
 341
 342		/* Unpin inode when detaching from connector */
 343		if (!(conn->flags & FSNOTIFY_CONN_FLAG_HAS_IREF))
 344			inode = NULL;
 345	} else if (conn->type == FSNOTIFY_OBJ_TYPE_VFSMOUNT) {
 346		fsnotify_conn_mount(conn)->mnt_fsnotify_mask = 0;
 347	} else if (conn->type == FSNOTIFY_OBJ_TYPE_SB) {
 348		fsnotify_conn_sb(conn)->s_fsnotify_mask = 0;
 349	}
 350
 351	rcu_assign_pointer(*connp, NULL);
 
 352	conn->obj = NULL;
 353	conn->type = FSNOTIFY_OBJ_TYPE_DETACHED;
 354	fsnotify_update_sb_watchers(sb, conn);
 355
 356	return inode;
 357}
 358
 359static void fsnotify_final_mark_destroy(struct fsnotify_mark *mark)
 360{
 361	struct fsnotify_group *group = mark->group;
 362
 363	if (WARN_ON_ONCE(!group))
 364		return;
 365	group->ops->free_mark(mark);
 366	fsnotify_put_group(group);
 367}
 368
 369/* Drop object reference originally held by a connector */
 370static void fsnotify_drop_object(unsigned int type, void *objp)
 371{
 372	if (!objp)
 373		return;
 374	/* Currently only inode references are passed to be dropped */
 375	if (WARN_ON_ONCE(type != FSNOTIFY_OBJ_TYPE_INODE))
 376		return;
 377	fsnotify_put_inode_ref(objp);
 378}
 379
 380void fsnotify_put_mark(struct fsnotify_mark *mark)
 381{
 382	struct fsnotify_mark_connector *conn = READ_ONCE(mark->connector);
 383	void *objp = NULL;
 384	unsigned int type = FSNOTIFY_OBJ_TYPE_DETACHED;
 385	bool free_conn = false;
 386
 387	/* Catch marks that were actually never attached to object */
 388	if (!conn) {
 389		if (refcount_dec_and_test(&mark->refcnt))
 390			fsnotify_final_mark_destroy(mark);
 391		return;
 392	}
 393
 394	/*
 395	 * We have to be careful so that traversals of obj_list under lock can
 396	 * safely grab mark reference.
 397	 */
 398	if (!refcount_dec_and_lock(&mark->refcnt, &conn->lock))
 399		return;
 400
 401	hlist_del_init_rcu(&mark->obj_list);
 402	if (hlist_empty(&conn->list)) {
 403		objp = fsnotify_detach_connector_from_object(conn, &type);
 404		free_conn = true;
 405	} else {
 406		struct super_block *sb = fsnotify_connector_sb(conn);
 407
 408		/* Update watched objects after detaching mark */
 409		if (sb)
 410			fsnotify_update_sb_watchers(sb, conn);
 411		objp = __fsnotify_recalc_mask(conn);
 412		type = conn->type;
 413	}
 414	WRITE_ONCE(mark->connector, NULL);
 415	spin_unlock(&conn->lock);
 416
 417	fsnotify_drop_object(type, objp);
 418
 419	if (free_conn) {
 420		spin_lock(&destroy_lock);
 421		conn->destroy_next = connector_destroy_list;
 422		connector_destroy_list = conn;
 423		spin_unlock(&destroy_lock);
 424		queue_work(system_unbound_wq, &connector_reaper_work);
 425	}
 426	/*
 427	 * Note that we didn't update flags telling whether inode cares about
 428	 * what's happening with children. We update these flags from
 429	 * __fsnotify_parent() lazily when next event happens on one of our
 430	 * children.
 431	 */
 432	spin_lock(&destroy_lock);
 433	list_add(&mark->g_list, &destroy_list);
 434	spin_unlock(&destroy_lock);
 435	queue_delayed_work(system_unbound_wq, &reaper_work,
 436			   FSNOTIFY_REAPER_DELAY);
 437}
 438EXPORT_SYMBOL_GPL(fsnotify_put_mark);
 439
 440/*
 441 * Get mark reference when we found the mark via lockless traversal of object
 442 * list. Mark can be already removed from the list by now and on its way to be
 443 * destroyed once SRCU period ends.
 444 *
 445 * Also pin the group so it doesn't disappear under us.
 446 */
 447static bool fsnotify_get_mark_safe(struct fsnotify_mark *mark)
 448{
 449	if (!mark)
 450		return true;
 451
 452	if (refcount_inc_not_zero(&mark->refcnt)) {
 453		spin_lock(&mark->lock);
 454		if (mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED) {
 455			/* mark is attached, group is still alive then */
 456			atomic_inc(&mark->group->user_waits);
 457			spin_unlock(&mark->lock);
 458			return true;
 459		}
 460		spin_unlock(&mark->lock);
 461		fsnotify_put_mark(mark);
 462	}
 463	return false;
 464}
 465
 466/*
 467 * Puts marks and wakes up group destruction if necessary.
 468 *
 469 * Pairs with fsnotify_get_mark_safe()
 470 */
 471static void fsnotify_put_mark_wake(struct fsnotify_mark *mark)
 472{
 473	if (mark) {
 474		struct fsnotify_group *group = mark->group;
 475
 476		fsnotify_put_mark(mark);
 477		/*
 478		 * We abuse notification_waitq on group shutdown for waiting for
 479		 * all marks pinned when waiting for userspace.
 480		 */
 481		if (atomic_dec_and_test(&group->user_waits) && group->shutdown)
 482			wake_up(&group->notification_waitq);
 483	}
 484}
 485
 486bool fsnotify_prepare_user_wait(struct fsnotify_iter_info *iter_info)
 487	__releases(&fsnotify_mark_srcu)
 488{
 489	int type;
 490
 491	fsnotify_foreach_iter_type(type) {
 492		/* This can fail if mark is being removed */
 493		if (!fsnotify_get_mark_safe(iter_info->marks[type])) {
 494			__release(&fsnotify_mark_srcu);
 495			goto fail;
 496		}
 497	}
 498
 499	/*
 500	 * Now that both marks are pinned by refcount in the inode / vfsmount
 501	 * lists, we can drop SRCU lock, and safely resume the list iteration
 502	 * once userspace returns.
 503	 */
 504	srcu_read_unlock(&fsnotify_mark_srcu, iter_info->srcu_idx);
 505
 506	return true;
 507
 508fail:
 509	for (type--; type >= 0; type--)
 510		fsnotify_put_mark_wake(iter_info->marks[type]);
 511	return false;
 512}
 513
 514void fsnotify_finish_user_wait(struct fsnotify_iter_info *iter_info)
 515	__acquires(&fsnotify_mark_srcu)
 516{
 517	int type;
 518
 519	iter_info->srcu_idx = srcu_read_lock(&fsnotify_mark_srcu);
 520	fsnotify_foreach_iter_type(type)
 521		fsnotify_put_mark_wake(iter_info->marks[type]);
 522}
 523
 524/*
 525 * Mark mark as detached, remove it from group list. Mark still stays in object
 526 * list until its last reference is dropped. Note that we rely on mark being
 527 * removed from group list before corresponding reference to it is dropped. In
 528 * particular we rely on mark->connector being valid while we hold
 529 * group->mark_mutex if we found the mark through g_list.
 530 *
 531 * Must be called with group->mark_mutex held. The caller must either hold
 532 * reference to the mark or be protected by fsnotify_mark_srcu.
 533 */
 534void fsnotify_detach_mark(struct fsnotify_mark *mark)
 535{
 536	fsnotify_group_assert_locked(mark->group);
 537	WARN_ON_ONCE(!srcu_read_lock_held(&fsnotify_mark_srcu) &&
 538		     refcount_read(&mark->refcnt) < 1 +
 539			!!(mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED));
 540
 541	spin_lock(&mark->lock);
 542	/* something else already called this function on this mark */
 543	if (!(mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) {
 544		spin_unlock(&mark->lock);
 545		return;
 546	}
 547	mark->flags &= ~FSNOTIFY_MARK_FLAG_ATTACHED;
 548	list_del_init(&mark->g_list);
 549	spin_unlock(&mark->lock);
 550
 551	/* Drop mark reference acquired in fsnotify_add_mark_locked() */
 552	fsnotify_put_mark(mark);
 553}
 554
 555/*
 556 * Free fsnotify mark. The mark is actually only marked as being freed.  The
 557 * freeing is actually happening only once last reference to the mark is
 558 * dropped from a workqueue which first waits for srcu period end.
 559 *
 560 * Caller must have a reference to the mark or be protected by
 561 * fsnotify_mark_srcu.
 562 */
 563void fsnotify_free_mark(struct fsnotify_mark *mark)
 564{
 565	struct fsnotify_group *group = mark->group;
 566
 567	spin_lock(&mark->lock);
 568	/* something else already called this function on this mark */
 569	if (!(mark->flags & FSNOTIFY_MARK_FLAG_ALIVE)) {
 570		spin_unlock(&mark->lock);
 571		return;
 572	}
 573	mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE;
 574	spin_unlock(&mark->lock);
 575
 576	/*
 577	 * Some groups like to know that marks are being freed.  This is a
 578	 * callback to the group function to let it know that this mark
 579	 * is being freed.
 580	 */
 581	if (group->ops->freeing_mark)
 582		group->ops->freeing_mark(mark, group);
 583}
 584
 585void fsnotify_destroy_mark(struct fsnotify_mark *mark,
 586			   struct fsnotify_group *group)
 587{
 588	fsnotify_group_lock(group);
 589	fsnotify_detach_mark(mark);
 590	fsnotify_group_unlock(group);
 591	fsnotify_free_mark(mark);
 592}
 593EXPORT_SYMBOL_GPL(fsnotify_destroy_mark);
 594
 595/*
 596 * Sorting function for lists of fsnotify marks.
 597 *
 598 * Fanotify supports different notification classes (reflected as priority of
 599 * notification group). Events shall be passed to notification groups in
 600 * decreasing priority order. To achieve this marks in notification lists for
 601 * inodes and vfsmounts are sorted so that priorities of corresponding groups
 602 * are descending.
 603 *
 604 * Furthermore correct handling of the ignore mask requires processing inode
 605 * and vfsmount marks of each group together. Using the group address as
 606 * further sort criterion provides a unique sorting order and thus we can
 607 * merge inode and vfsmount lists of marks in linear time and find groups
 608 * present in both lists.
 609 *
 610 * A return value of 1 signifies that b has priority over a.
 611 * A return value of 0 signifies that the two marks have to be handled together.
 612 * A return value of -1 signifies that a has priority over b.
 613 */
 614int fsnotify_compare_groups(struct fsnotify_group *a, struct fsnotify_group *b)
 615{
 616	if (a == b)
 617		return 0;
 618	if (!a)
 619		return 1;
 620	if (!b)
 621		return -1;
 622	if (a->priority < b->priority)
 623		return 1;
 624	if (a->priority > b->priority)
 625		return -1;
 626	if (a < b)
 627		return 1;
 628	return -1;
 629}
 630
 631static int fsnotify_attach_info_to_sb(struct super_block *sb)
 632{
 633	struct fsnotify_sb_info *sbinfo;
 634
 635	/* sb info is freed on fsnotify_sb_delete() */
 636	sbinfo = kzalloc(sizeof(*sbinfo), GFP_KERNEL);
 637	if (!sbinfo)
 638		return -ENOMEM;
 639
 640	/*
 641	 * cmpxchg() provides the barrier so that callers of fsnotify_sb_info()
 642	 * will observe an initialized structure
 643	 */
 644	if (cmpxchg(&sb->s_fsnotify_info, NULL, sbinfo)) {
 645		/* Someone else created sbinfo for us */
 646		kfree(sbinfo);
 647	}
 648	return 0;
 649}
 650
 651static int fsnotify_attach_connector_to_object(fsnotify_connp_t *connp,
 652					       void *obj, unsigned int obj_type)
 653{
 654	struct fsnotify_mark_connector *conn;
 655
 656	conn = kmem_cache_alloc(fsnotify_mark_connector_cachep, GFP_KERNEL);
 657	if (!conn)
 658		return -ENOMEM;
 659	spin_lock_init(&conn->lock);
 660	INIT_HLIST_HEAD(&conn->list);
 661	conn->flags = 0;
 662	conn->prio = 0;
 663	conn->type = obj_type;
 664	conn->obj = obj;
 
 
 665
 666	/*
 667	 * cmpxchg() provides the barrier so that readers of *connp can see
 668	 * only initialized structure
 669	 */
 670	if (cmpxchg(connp, NULL, conn)) {
 671		/* Someone else created list structure for us */
 
 672		kmem_cache_free(fsnotify_mark_connector_cachep, conn);
 673	}
 
 674	return 0;
 675}
 676
 677/*
 678 * Get mark connector, make sure it is alive and return with its lock held.
 679 * This is for users that get connector pointer from inode or mount. Users that
 680 * hold reference to a mark on the list may directly lock connector->lock as
 681 * they are sure list cannot go away under them.
 682 */
 683static struct fsnotify_mark_connector *fsnotify_grab_connector(
 684						fsnotify_connp_t *connp)
 685{
 686	struct fsnotify_mark_connector *conn;
 687	int idx;
 688
 689	idx = srcu_read_lock(&fsnotify_mark_srcu);
 690	conn = srcu_dereference(*connp, &fsnotify_mark_srcu);
 691	if (!conn)
 692		goto out;
 693	spin_lock(&conn->lock);
 694	if (conn->type == FSNOTIFY_OBJ_TYPE_DETACHED) {
 695		spin_unlock(&conn->lock);
 696		srcu_read_unlock(&fsnotify_mark_srcu, idx);
 697		return NULL;
 698	}
 699out:
 700	srcu_read_unlock(&fsnotify_mark_srcu, idx);
 701	return conn;
 702}
 703
 704/*
 705 * Add mark into proper place in given list of marks. These marks may be used
 706 * for the fsnotify backend to determine which event types should be delivered
 707 * to which group and for which inodes. These marks are ordered according to
 708 * priority, highest number first, and then by the group's location in memory.
 709 */
 710static int fsnotify_add_mark_list(struct fsnotify_mark *mark, void *obj,
 
 711				  unsigned int obj_type, int add_flags)
 712{
 713	struct super_block *sb = fsnotify_object_sb(obj, obj_type);
 714	struct fsnotify_mark *lmark, *last = NULL;
 715	struct fsnotify_mark_connector *conn;
 716	fsnotify_connp_t *connp;
 717	int cmp;
 718	int err = 0;
 719
 720	if (WARN_ON(!fsnotify_valid_obj_type(obj_type)))
 721		return -EINVAL;
 722
 723	/*
 724	 * Attach the sb info before attaching a connector to any object on sb.
 725	 * The sb info will remain attached as long as sb lives.
 726	 */
 727	if (!fsnotify_sb_info(sb)) {
 728		err = fsnotify_attach_info_to_sb(sb);
 729		if (err)
 730			return err;
 731	}
 732
 733	connp = fsnotify_object_connp(obj, obj_type);
 734restart:
 735	spin_lock(&mark->lock);
 736	conn = fsnotify_grab_connector(connp);
 737	if (!conn) {
 738		spin_unlock(&mark->lock);
 739		err = fsnotify_attach_connector_to_object(connp, obj, obj_type);
 740		if (err)
 741			return err;
 742		goto restart;
 743	}
 744
 745	/* is mark the first mark? */
 746	if (hlist_empty(&conn->list)) {
 747		hlist_add_head_rcu(&mark->obj_list, &conn->list);
 748		goto added;
 749	}
 750
 751	/* should mark be in the middle of the current list? */
 752	hlist_for_each_entry(lmark, &conn->list, obj_list) {
 753		last = lmark;
 754
 755		if ((lmark->group == mark->group) &&
 756		    (lmark->flags & FSNOTIFY_MARK_FLAG_ATTACHED) &&
 757		    !(mark->group->flags & FSNOTIFY_GROUP_DUPS)) {
 758			err = -EEXIST;
 759			goto out_err;
 760		}
 761
 762		cmp = fsnotify_compare_groups(lmark->group, mark->group);
 763		if (cmp >= 0) {
 764			hlist_add_before_rcu(&mark->obj_list, &lmark->obj_list);
 765			goto added;
 766		}
 767	}
 768
 769	BUG_ON(last == NULL);
 770	/* mark should be the last entry.  last is the current last entry */
 771	hlist_add_behind_rcu(&mark->obj_list, &last->obj_list);
 772added:
 773	fsnotify_update_sb_watchers(sb, conn);
 774	/*
 775	 * Since connector is attached to object using cmpxchg() we are
 776	 * guaranteed that connector initialization is fully visible by anyone
 777	 * seeing mark->connector set.
 778	 */
 779	WRITE_ONCE(mark->connector, conn);
 780out_err:
 781	spin_unlock(&conn->lock);
 782	spin_unlock(&mark->lock);
 783	return err;
 784}
 785
 786/*
 787 * Attach an initialized mark to a given group and fs object.
 788 * These marks may be used for the fsnotify backend to determine which
 789 * event types should be delivered to which group.
 790 */
 791int fsnotify_add_mark_locked(struct fsnotify_mark *mark,
 792			     void *obj, unsigned int obj_type,
 793			     int add_flags)
 794{
 795	struct fsnotify_group *group = mark->group;
 796	int ret = 0;
 797
 798	fsnotify_group_assert_locked(group);
 799
 800	/*
 801	 * LOCKING ORDER!!!!
 802	 * group->mark_mutex
 803	 * mark->lock
 804	 * mark->connector->lock
 805	 */
 806	spin_lock(&mark->lock);
 807	mark->flags |= FSNOTIFY_MARK_FLAG_ALIVE | FSNOTIFY_MARK_FLAG_ATTACHED;
 808
 809	list_add(&mark->g_list, &group->marks_list);
 810	fsnotify_get_mark(mark); /* for g_list */
 811	spin_unlock(&mark->lock);
 812
 813	ret = fsnotify_add_mark_list(mark, obj, obj_type, add_flags);
 814	if (ret)
 815		goto err;
 816
 817	fsnotify_recalc_mask(mark->connector);
 818
 819	return ret;
 820err:
 821	spin_lock(&mark->lock);
 822	mark->flags &= ~(FSNOTIFY_MARK_FLAG_ALIVE |
 823			 FSNOTIFY_MARK_FLAG_ATTACHED);
 824	list_del_init(&mark->g_list);
 825	spin_unlock(&mark->lock);
 826
 827	fsnotify_put_mark(mark);
 828	return ret;
 829}
 830
 831int fsnotify_add_mark(struct fsnotify_mark *mark, void *obj,
 832		      unsigned int obj_type, int add_flags)
 833{
 834	int ret;
 835	struct fsnotify_group *group = mark->group;
 836
 837	fsnotify_group_lock(group);
 838	ret = fsnotify_add_mark_locked(mark, obj, obj_type, add_flags);
 839	fsnotify_group_unlock(group);
 840	return ret;
 841}
 842EXPORT_SYMBOL_GPL(fsnotify_add_mark);
 843
 844/*
 845 * Given a list of marks, find the mark associated with given group. If found
 846 * take a reference to that mark and return it, else return NULL.
 847 */
 848struct fsnotify_mark *fsnotify_find_mark(void *obj, unsigned int obj_type,
 849					 struct fsnotify_group *group)
 850{
 851	fsnotify_connp_t *connp = fsnotify_object_connp(obj, obj_type);
 852	struct fsnotify_mark_connector *conn;
 853	struct fsnotify_mark *mark;
 854
 855	if (!connp)
 856		return NULL;
 857
 858	conn = fsnotify_grab_connector(connp);
 859	if (!conn)
 860		return NULL;
 861
 862	hlist_for_each_entry(mark, &conn->list, obj_list) {
 863		if (mark->group == group &&
 864		    (mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) {
 865			fsnotify_get_mark(mark);
 866			spin_unlock(&conn->lock);
 867			return mark;
 868		}
 869	}
 870	spin_unlock(&conn->lock);
 871	return NULL;
 872}
 873EXPORT_SYMBOL_GPL(fsnotify_find_mark);
 874
 875/* Clear any marks in a group with given type mask */
 876void fsnotify_clear_marks_by_group(struct fsnotify_group *group,
 877				   unsigned int obj_type)
 878{
 879	struct fsnotify_mark *lmark, *mark;
 880	LIST_HEAD(to_free);
 881	struct list_head *head = &to_free;
 882
 883	/* Skip selection step if we want to clear all marks. */
 884	if (obj_type == FSNOTIFY_OBJ_TYPE_ANY) {
 885		head = &group->marks_list;
 886		goto clear;
 887	}
 888	/*
 889	 * We have to be really careful here. Anytime we drop mark_mutex, e.g.
 890	 * fsnotify_clear_marks_by_inode() can come and free marks. Even in our
 891	 * to_free list so we have to use mark_mutex even when accessing that
 892	 * list. And freeing mark requires us to drop mark_mutex. So we can
 893	 * reliably free only the first mark in the list. That's why we first
 894	 * move marks to free to to_free list in one go and then free marks in
 895	 * to_free list one by one.
 896	 */
 897	fsnotify_group_lock(group);
 898	list_for_each_entry_safe(mark, lmark, &group->marks_list, g_list) {
 899		if (mark->connector->type == obj_type)
 900			list_move(&mark->g_list, &to_free);
 901	}
 902	fsnotify_group_unlock(group);
 903
 904clear:
 905	while (1) {
 906		fsnotify_group_lock(group);
 907		if (list_empty(head)) {
 908			fsnotify_group_unlock(group);
 909			break;
 910		}
 911		mark = list_first_entry(head, struct fsnotify_mark, g_list);
 912		fsnotify_get_mark(mark);
 913		fsnotify_detach_mark(mark);
 914		fsnotify_group_unlock(group);
 915		fsnotify_free_mark(mark);
 916		fsnotify_put_mark(mark);
 917	}
 918}
 919
 920/* Destroy all marks attached to an object via connector */
 921void fsnotify_destroy_marks(fsnotify_connp_t *connp)
 922{
 923	struct fsnotify_mark_connector *conn;
 924	struct fsnotify_mark *mark, *old_mark = NULL;
 925	void *objp;
 926	unsigned int type;
 927
 928	conn = fsnotify_grab_connector(connp);
 929	if (!conn)
 930		return;
 931	/*
 932	 * We have to be careful since we can race with e.g.
 933	 * fsnotify_clear_marks_by_group() and once we drop the conn->lock, the
 934	 * list can get modified. However we are holding mark reference and
 935	 * thus our mark cannot be removed from obj_list so we can continue
 936	 * iteration after regaining conn->lock.
 937	 */
 938	hlist_for_each_entry(mark, &conn->list, obj_list) {
 939		fsnotify_get_mark(mark);
 940		spin_unlock(&conn->lock);
 941		if (old_mark)
 942			fsnotify_put_mark(old_mark);
 943		old_mark = mark;
 944		fsnotify_destroy_mark(mark, mark->group);
 945		spin_lock(&conn->lock);
 946	}
 947	/*
 948	 * Detach list from object now so that we don't pin inode until all
 949	 * mark references get dropped. It would lead to strange results such
 950	 * as delaying inode deletion or blocking unmount.
 951	 */
 952	objp = fsnotify_detach_connector_from_object(conn, &type);
 953	spin_unlock(&conn->lock);
 954	if (old_mark)
 955		fsnotify_put_mark(old_mark);
 956	fsnotify_drop_object(type, objp);
 957}
 958
 959/*
 960 * Nothing fancy, just initialize lists and locks and counters.
 961 */
 962void fsnotify_init_mark(struct fsnotify_mark *mark,
 963			struct fsnotify_group *group)
 964{
 965	memset(mark, 0, sizeof(*mark));
 966	spin_lock_init(&mark->lock);
 967	refcount_set(&mark->refcnt, 1);
 968	fsnotify_get_group(group);
 969	mark->group = group;
 970	WRITE_ONCE(mark->connector, NULL);
 971}
 972EXPORT_SYMBOL_GPL(fsnotify_init_mark);
 973
 974/*
 975 * Destroy all marks in destroy_list, waits for SRCU period to finish before
 976 * actually freeing marks.
 977 */
 978static void fsnotify_mark_destroy_workfn(struct work_struct *work)
 979{
 980	struct fsnotify_mark *mark, *next;
 981	struct list_head private_destroy_list;
 982
 983	spin_lock(&destroy_lock);
 984	/* exchange the list head */
 985	list_replace_init(&destroy_list, &private_destroy_list);
 986	spin_unlock(&destroy_lock);
 987
 988	synchronize_srcu(&fsnotify_mark_srcu);
 989
 990	list_for_each_entry_safe(mark, next, &private_destroy_list, g_list) {
 991		list_del_init(&mark->g_list);
 992		fsnotify_final_mark_destroy(mark);
 993	}
 994}
 995
 996/* Wait for all marks queued for destruction to be actually destroyed */
 997void fsnotify_wait_marks_destroyed(void)
 998{
 999	flush_delayed_work(&reaper_work);
1000}
1001EXPORT_SYMBOL_GPL(fsnotify_wait_marks_destroyed);