diff options
Diffstat (limited to 'fs/notify/mark.c')
| -rw-r--r-- | fs/notify/mark.c | 1194 |
1 files changed, 1194 insertions, 0 deletions
diff --git a/fs/notify/mark.c b/fs/notify/mark.c new file mode 100644 index 000000000..b2640d836 --- /dev/null +++ b/fs/notify/mark.c @@ -0,0 +1,1194 @@ +// SPDX-License-Identifier: GPL-2.0-or-later +/* + * Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com> + */ + +/* + * fsnotify inode mark locking/lifetime/and refcnting + * + * REFCNT: + * The group->recnt and mark->refcnt tell how many "things" in the kernel + * currently are referencing the objects. Both kind of objects typically will + * live inside the kernel with a refcnt of 2, one for its creation and one for + * the reference a group and a mark hold to each other. + * If you are holding the appropriate locks, you can take a reference and the + * object itself is guaranteed to survive until the reference is dropped. + * + * LOCKING: + * There are 3 locks involved with fsnotify inode marks and they MUST be taken + * in order as follows: + * + * group->mark_mutex + * mark->lock + * mark->connector->lock + * + * group->mark_mutex protects the marks_list anchored inside a given group and + * each mark is hooked via the g_list. It also protects the groups private + * data (i.e group limits). + + * mark->lock protects the marks attributes like its masks and flags. + * Furthermore it protects the access to a reference of the group that the mark + * is assigned to as well as the access to a reference of the inode/vfsmount + * that is being watched by the mark. + * + * mark->connector->lock protects the list of marks anchored inside an + * inode / vfsmount and each mark is hooked via the i_list. + * + * A list of notification marks relating to inode / mnt is contained in + * fsnotify_mark_connector. That structure is alive as long as there are any + * marks in the list and is also protected by fsnotify_mark_srcu. A mark gets + * detached from fsnotify_mark_connector when last reference to the mark is + * dropped. Thus having mark reference is enough to protect mark->connector + * pointer and to make sure fsnotify_mark_connector cannot disappear. Also + * because we remove mark from g_list before dropping mark reference associated + * with that, any mark found through g_list is guaranteed to have + * mark->connector set until we drop group->mark_mutex. + * + * LIFETIME: + * Inode marks survive between when they are added to an inode and when their + * refcnt==0. Marks are also protected by fsnotify_mark_srcu. + * + * The inode mark can be cleared for a number of different reasons including: + * - The inode is unlinked for the last time. (fsnotify_inode_remove) + * - The inode is being evicted from cache. (fsnotify_inode_delete) + * - The fs the inode is on is unmounted. (fsnotify_inode_delete/fsnotify_unmount_inodes) + * - Something explicitly requests that it be removed. (fsnotify_destroy_mark) + * - The fsnotify_group associated with the mark is going away and all such marks + * need to be cleaned up. (fsnotify_clear_marks_by_group) + * + * This has the very interesting property of being able to run concurrently with + * any (or all) other directions. + */ + +#include <linux/fs.h> +#include <linux/init.h> +#include <linux/kernel.h> +#include <linux/kthread.h> +#include <linux/module.h> +#include <linux/mutex.h> +#include <linux/slab.h> +#include <linux/spinlock.h> +#include <linux/srcu.h> +#include <linux/ratelimit.h> + +#include <linux/atomic.h> + +#include <linux/fsnotify_backend.h> +#include "fsnotify.h" + +#define FSNOTIFY_REAPER_DELAY (1) /* 1 jiffy */ + +struct srcu_struct fsnotify_mark_srcu; +static struct kmem_cache *fsnotify_mark_connector_cachep; +static struct kmem_cache *fsnotify_inode_mark_connector_cachep; + +static DEFINE_SPINLOCK(destroy_lock); +static LIST_HEAD(destroy_list); +static struct fsnotify_mark_connector *connector_destroy_list; + +static void fsnotify_mark_destroy_workfn(struct work_struct *work); +static DECLARE_DELAYED_WORK(reaper_work, fsnotify_mark_destroy_workfn); + +static void fsnotify_connector_destroy_workfn(struct work_struct *work); +static DECLARE_WORK(connector_reaper_work, fsnotify_connector_destroy_workfn); + +void fsnotify_get_mark(struct fsnotify_mark *mark) +{ + WARN_ON_ONCE(!refcount_read(&mark->refcnt)); + refcount_inc(&mark->refcnt); +} + +static fsnotify_connp_t *fsnotify_object_connp(void *obj, + enum fsnotify_obj_type obj_type) +{ + switch (obj_type) { + case FSNOTIFY_OBJ_TYPE_INODE: + return &((struct inode *)obj)->i_fsnotify_marks; + case FSNOTIFY_OBJ_TYPE_VFSMOUNT: + return &real_mount(obj)->mnt_fsnotify_marks; + case FSNOTIFY_OBJ_TYPE_SB: + return fsnotify_sb_marks(obj); + case FSNOTIFY_OBJ_TYPE_MNTNS: + return &((struct mnt_namespace *)obj)->n_fsnotify_marks; + default: + return NULL; + } +} + +static __u32 *fsnotify_conn_mask_p(struct fsnotify_mark_connector *conn) +{ + if (conn->type == FSNOTIFY_OBJ_TYPE_INODE) + return &fsnotify_conn_inode(conn)->i_fsnotify_mask; + else if (conn->type == FSNOTIFY_OBJ_TYPE_VFSMOUNT) + return &fsnotify_conn_mount(conn)->mnt_fsnotify_mask; + else if (conn->type == FSNOTIFY_OBJ_TYPE_SB) + return &fsnotify_conn_sb(conn)->s_fsnotify_mask; + else if (conn->type == FSNOTIFY_OBJ_TYPE_MNTNS) + return &fsnotify_conn_mntns(conn)->n_fsnotify_mask; + return NULL; +} + +__u32 fsnotify_conn_mask(struct fsnotify_mark_connector *conn) +{ + if (WARN_ON(!fsnotify_valid_obj_type(conn->type))) + return 0; + + return READ_ONCE(*fsnotify_conn_mask_p(conn)); +} + +static void fsnotify_get_sb_watched_objects(struct super_block *sb) +{ + atomic_long_inc(fsnotify_sb_watched_objects(sb)); +} + +static void fsnotify_put_sb_watched_objects(struct super_block *sb) +{ + atomic_long_t *watched_objects = fsnotify_sb_watched_objects(sb); + + /* the superblock can go away after this decrement */ + if (atomic_long_dec_and_test(watched_objects)) + wake_up_var(watched_objects); +} + +static void fsnotify_get_inode_ref(struct inode *inode) +{ + ihold(inode); + fsnotify_get_sb_watched_objects(inode->i_sb); +} + +static void fsnotify_put_inode_ref(struct inode *inode) +{ + /* read ->i_sb before the inode can go away */ + struct super_block *sb = inode->i_sb; + + iput(inode); + fsnotify_put_sb_watched_objects(sb); +} + +/* + * Grab or drop watched objects reference depending on whether the connector + * is attached and has any marks attached. + */ +static void fsnotify_update_sb_watchers(struct super_block *sb, + struct fsnotify_mark_connector *conn) +{ + struct fsnotify_sb_info *sbinfo = fsnotify_sb_info(sb); + bool is_watched = conn->flags & FSNOTIFY_CONN_FLAG_IS_WATCHED; + struct fsnotify_mark *first_mark = NULL; + unsigned int highest_prio = 0; + + if (conn->obj) + first_mark = hlist_entry_safe(conn->list.first, + struct fsnotify_mark, obj_list); + if (first_mark) + highest_prio = first_mark->group->priority; + if (WARN_ON(highest_prio >= __FSNOTIFY_PRIO_NUM)) + highest_prio = 0; + + /* + * If the highest priority of group watching this object is prio, + * then watched object has a reference on counters [0..prio]. + * Update priority >= 1 watched objects counters. + */ + for (unsigned int p = conn->prio + 1; p <= highest_prio; p++) + atomic_long_inc(&sbinfo->watched_objects[p]); + for (unsigned int p = conn->prio; p > highest_prio; p--) + atomic_long_dec(&sbinfo->watched_objects[p]); + conn->prio = highest_prio; + + /* Update priority >= 0 (a.k.a total) watched objects counter */ + BUILD_BUG_ON(FSNOTIFY_PRIO_NORMAL != 0); + if (first_mark && !is_watched) { + conn->flags |= FSNOTIFY_CONN_FLAG_IS_WATCHED; + fsnotify_get_sb_watched_objects(sb); + } else if (!first_mark && is_watched) { + conn->flags &= ~FSNOTIFY_CONN_FLAG_IS_WATCHED; + fsnotify_put_sb_watched_objects(sb); + } +} + +/* + * Grab or drop inode reference for the connector if needed. + * + * When it's time to drop the reference, we only clear the HAS_IREF flag and + * return the inode object. fsnotify_drop_object() will be resonsible for doing + * iput() outside of spinlocks. This happens when last mark that wanted iref is + * detached. + */ +static struct inode *fsnotify_update_iref(struct fsnotify_mark_connector *conn, + bool want_iref) +{ + bool has_iref = conn->flags & FSNOTIFY_CONN_FLAG_HAS_IREF; + struct inode *inode = NULL; + + if (conn->type != FSNOTIFY_OBJ_TYPE_INODE || + want_iref == has_iref) + return NULL; + + if (want_iref) { + /* Pin inode if any mark wants inode refcount held */ + fsnotify_get_inode_ref(fsnotify_conn_inode(conn)); + conn->flags |= FSNOTIFY_CONN_FLAG_HAS_IREF; + } else { + /* Unpin inode after detach of last mark that wanted iref */ + inode = fsnotify_conn_inode(conn); + conn->flags &= ~FSNOTIFY_CONN_FLAG_HAS_IREF; + } + + return inode; +} + +/* + * Calculate mask of events for a list of marks. + * + * Return true if any of the attached marks want to hold an inode reference. + */ +static bool __fsnotify_recalc_mask(struct fsnotify_mark_connector *conn) +{ + u32 new_mask = 0; + bool want_iref = false; + struct fsnotify_mark *mark; + + assert_spin_locked(&conn->lock); + /* We can get detached connector here when inode is getting unlinked. */ + if (!fsnotify_valid_obj_type(conn->type)) + return NULL; + hlist_for_each_entry(mark, &conn->list, obj_list) { + if (!(mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) + continue; + new_mask |= fsnotify_calc_mask(mark); + if (conn->type == FSNOTIFY_OBJ_TYPE_INODE && + !(mark->flags & FSNOTIFY_MARK_FLAG_NO_IREF)) + want_iref = true; + } + /* + * We use WRITE_ONCE() to prevent silly compiler optimizations from + * confusing readers not holding conn->lock with partial updates. + */ + WRITE_ONCE(*fsnotify_conn_mask_p(conn), new_mask); + + return want_iref; +} + +/* + * Calculate mask of events for a list of marks after attach/modify mark + * and get an inode reference for the connector if needed. + * + * A concurrent add of evictable mark and detach of non-evictable mark can + * lead to __fsnotify_recalc_mask() returning false want_iref, but in this + * case we defer clearing iref to fsnotify_recalc_mask_clear_iref() called + * from fsnotify_put_mark(). + */ +static void fsnotify_recalc_mask_set_iref(struct fsnotify_mark_connector *conn) +{ + bool has_iref = conn->flags & FSNOTIFY_CONN_FLAG_HAS_IREF; + bool want_iref = __fsnotify_recalc_mask(conn) || has_iref; + + (void) fsnotify_update_iref(conn, want_iref); +} + +/* + * Calculate mask of events for a list of marks after detach mark + * and return the inode object if its reference is no longer needed. + */ +static void *fsnotify_recalc_mask_clear_iref(struct fsnotify_mark_connector *conn) +{ + bool want_iref = __fsnotify_recalc_mask(conn); + + return fsnotify_update_iref(conn, want_iref); +} + +static bool fsnotify_conn_watches_children( + struct fsnotify_mark_connector *conn) +{ + if (conn->type != FSNOTIFY_OBJ_TYPE_INODE) + return false; + + return fsnotify_inode_watches_children(fsnotify_conn_inode(conn)); +} + +static void fsnotify_conn_set_children_dentry_flags( + struct fsnotify_mark_connector *conn) +{ + if (conn->type != FSNOTIFY_OBJ_TYPE_INODE) + return; + + fsnotify_set_children_dentry_flags(fsnotify_conn_inode(conn)); +} + +/* + * Calculate mask of events for a list of marks. The caller must make sure + * connector and connector->obj cannot disappear under us. Callers achieve + * this by holding a mark->lock or mark->group->mark_mutex for a mark on this + * list. + */ +void fsnotify_recalc_mask(struct fsnotify_mark_connector *conn) +{ + bool update_children; + + if (!conn) + return; + + spin_lock(&conn->lock); + update_children = !fsnotify_conn_watches_children(conn); + fsnotify_recalc_mask_set_iref(conn); + update_children &= fsnotify_conn_watches_children(conn); + spin_unlock(&conn->lock); + /* + * Set children's PARENT_WATCHED flags only if parent started watching. + * When parent stops watching, we clear false positive PARENT_WATCHED + * flags lazily in __fsnotify_parent(). + */ + if (update_children) + fsnotify_conn_set_children_dentry_flags(conn); +} + +/** + * fsnotify_modify_mark_mask - set and/or clear flags in a mark's mask + * @mark: mark to be modified + * @set: bits to be set in mask + * @clear: bits to be cleared in mask + * + * Modify a fsnotify_mark mask as directed, and update its associated conn. + * The caller is expected to hold a reference to the mark. + */ +void fsnotify_modify_mark_mask(struct fsnotify_mark *mark, u32 set, u32 clear) +{ + bool recalc = false; + u32 mask; + + WARN_ON_ONCE(clear & set); + + spin_lock(&mark->lock); + mask = mark->mask; + mark->mask |= set; + mark->mask &= ~clear; + if (mark->mask != mask) + recalc = true; + spin_unlock(&mark->lock); + + if (recalc) + fsnotify_recalc_mask(mark->connector); +} +EXPORT_SYMBOL_GPL(fsnotify_modify_mark_mask); + +/* Free all connectors queued for freeing once SRCU period ends */ +static void fsnotify_connector_destroy_workfn(struct work_struct *work) +{ + struct fsnotify_mark_connector *conn, *free; + + spin_lock(&destroy_lock); + conn = connector_destroy_list; + connector_destroy_list = NULL; + spin_unlock(&destroy_lock); + + synchronize_srcu(&fsnotify_mark_srcu); + while (conn) { + free = conn; + conn = conn->destroy_next; + kfree(free); + } +} + +static void fsnotify_untrack_connector(struct fsnotify_mark_connector *conn); + +static void *fsnotify_detach_connector_from_object( + struct fsnotify_mark_connector *conn, + unsigned int *type) +{ + fsnotify_connp_t *connp = fsnotify_object_connp(conn->obj, conn->type); + struct super_block *sb = fsnotify_connector_sb(conn); + struct inode *inode = NULL; + + *type = conn->type; + if (conn->type == FSNOTIFY_OBJ_TYPE_DETACHED) + return NULL; + + if (conn->type == FSNOTIFY_OBJ_TYPE_INODE) { + inode = fsnotify_conn_inode(conn); + inode->i_fsnotify_mask = 0; + fsnotify_untrack_connector(conn); + + /* Unpin inode when detaching from connector */ + if (!(conn->flags & FSNOTIFY_CONN_FLAG_HAS_IREF)) + inode = NULL; + } else if (conn->type == FSNOTIFY_OBJ_TYPE_VFSMOUNT) { + fsnotify_conn_mount(conn)->mnt_fsnotify_mask = 0; + } else if (conn->type == FSNOTIFY_OBJ_TYPE_SB) { + fsnotify_conn_sb(conn)->s_fsnotify_mask = 0; + } else if (conn->type == FSNOTIFY_OBJ_TYPE_MNTNS) { + fsnotify_conn_mntns(conn)->n_fsnotify_mask = 0; + } + + rcu_assign_pointer(*connp, NULL); + conn->obj = NULL; + conn->type = FSNOTIFY_OBJ_TYPE_DETACHED; + if (sb) + fsnotify_update_sb_watchers(sb, conn); + + return inode; +} + +static void fsnotify_final_mark_destroy(struct fsnotify_mark *mark) +{ + struct fsnotify_group *group = mark->group; + + if (WARN_ON_ONCE(!group)) + return; + group->ops->free_mark(mark); + fsnotify_put_group(group); +} + +/* Drop object reference originally held by a connector */ +static void fsnotify_drop_object(unsigned int type, void *objp) +{ + if (!objp) + return; + /* Currently only inode references are passed to be dropped */ + if (WARN_ON_ONCE(type != FSNOTIFY_OBJ_TYPE_INODE)) + return; + fsnotify_put_inode_ref(objp); +} + +void fsnotify_put_mark(struct fsnotify_mark *mark) +{ + struct fsnotify_mark_connector *conn = READ_ONCE(mark->connector); + void *objp = NULL; + unsigned int type = FSNOTIFY_OBJ_TYPE_DETACHED; + bool free_conn = false; + + /* Catch marks that were actually never attached to object */ + if (!conn) { + if (refcount_dec_and_test(&mark->refcnt)) + fsnotify_final_mark_destroy(mark); + return; + } + + /* + * We have to be careful so that traversals of obj_list under lock can + * safely grab mark reference. + */ + if (!refcount_dec_and_lock(&mark->refcnt, &conn->lock)) + return; + + hlist_del_init_rcu(&mark->obj_list); + if (hlist_empty(&conn->list)) { + objp = fsnotify_detach_connector_from_object(conn, &type); + free_conn = true; + } else { + struct super_block *sb = fsnotify_connector_sb(conn); + + /* Update watched objects after detaching mark */ + if (sb) + fsnotify_update_sb_watchers(sb, conn); + objp = fsnotify_recalc_mask_clear_iref(conn); + type = conn->type; + } + WRITE_ONCE(mark->connector, NULL); + spin_unlock(&conn->lock); + + fsnotify_drop_object(type, objp); + + if (free_conn) { + spin_lock(&destroy_lock); + conn->destroy_next = connector_destroy_list; + connector_destroy_list = conn; + spin_unlock(&destroy_lock); + queue_work(system_dfl_wq, &connector_reaper_work); + } + /* + * Note that we didn't update flags telling whether inode cares about + * what's happening with children. We update these flags from + * __fsnotify_parent() lazily when next event happens on one of our + * children. + */ + spin_lock(&destroy_lock); + list_add(&mark->g_list, &destroy_list); + spin_unlock(&destroy_lock); + queue_delayed_work(system_dfl_wq, &reaper_work, + FSNOTIFY_REAPER_DELAY); +} +EXPORT_SYMBOL_GPL(fsnotify_put_mark); + +/* + * Get mark reference when we found the mark via lockless traversal of object + * list. Mark can be already removed from the list by now and on its way to be + * destroyed once SRCU period ends. + * + * Also pin the group so it doesn't disappear under us. + */ +static bool fsnotify_get_mark_safe(struct fsnotify_mark *mark) +{ + if (refcount_inc_not_zero(&mark->refcnt)) { + spin_lock(&mark->lock); + if (mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED) { + /* mark is attached, group is still alive then */ + atomic_inc(&mark->group->user_waits); + spin_unlock(&mark->lock); + return true; + } + spin_unlock(&mark->lock); + fsnotify_put_mark(mark); + } + return false; +} + +/* + * Puts marks and wakes up group destruction if necessary. + * + * Pairs with fsnotify_get_mark_safe() + */ +static void fsnotify_put_mark_wake(struct fsnotify_mark *mark) +{ + if (mark) { + struct fsnotify_group *group = mark->group; + + fsnotify_put_mark(mark); + /* + * We abuse notification_waitq on group shutdown for waiting for + * all marks pinned when waiting for userspace. + */ + if (atomic_dec_and_test(&group->user_waits) && group->shutdown) + wake_up(&group->notification_waitq); + } +} + +bool fsnotify_prepare_user_wait(struct fsnotify_iter_info *iter_info) + __releases(&fsnotify_mark_srcu) +{ + int type; + + fsnotify_foreach_iter_type(type) { + struct fsnotify_mark *mark = iter_info->marks[type]; + + /* This can fail if mark is being removed */ + while (mark && !fsnotify_get_mark_safe(mark)) { + if (mark->group == iter_info->current_group) { + __release(&fsnotify_mark_srcu); + goto fail; + } + /* This is a mark in an unrelated group, skip */ + mark = fsnotify_next_mark(mark); + iter_info->marks[type] = mark; + } + } + + /* + * Now that all marks are pinned by refcount in the inode / vfsmount / etc + * lists, we can drop SRCU lock, and safely resume the list iteration + * once userspace returns. + */ + srcu_read_unlock(&fsnotify_mark_srcu, iter_info->srcu_idx); + + return true; + +fail: + for (type--; type >= 0; type--) + fsnotify_put_mark_wake(iter_info->marks[type]); + return false; +} + +void fsnotify_finish_user_wait(struct fsnotify_iter_info *iter_info) + __acquires(&fsnotify_mark_srcu) +{ + int type; + + iter_info->srcu_idx = srcu_read_lock(&fsnotify_mark_srcu); + fsnotify_foreach_iter_type(type) + fsnotify_put_mark_wake(iter_info->marks[type]); +} + +/* + * Mark mark as detached, remove it from group list. Mark still stays in object + * list until its last reference is dropped. Note that we rely on mark being + * removed from group list before corresponding reference to it is dropped. In + * particular we rely on mark->connector being valid while we hold + * group->mark_mutex if we found the mark through g_list. + * + * Must be called with group->mark_mutex held. The caller must either hold + * reference to the mark or be protected by fsnotify_mark_srcu. + */ +void fsnotify_detach_mark(struct fsnotify_mark *mark) +{ + fsnotify_group_assert_locked(mark->group); + WARN_ON_ONCE(!srcu_read_lock_held(&fsnotify_mark_srcu) && + refcount_read(&mark->refcnt) < 1 + + !!(mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)); + + spin_lock(&mark->lock); + /* something else already called this function on this mark */ + if (!(mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) { + spin_unlock(&mark->lock); + return; + } + mark->flags &= ~FSNOTIFY_MARK_FLAG_ATTACHED; + list_del_init(&mark->g_list); + spin_unlock(&mark->lock); + + /* Drop mark reference acquired in fsnotify_add_mark_locked() */ + fsnotify_put_mark(mark); +} + +/* + * Free fsnotify mark. The mark is actually only marked as being freed. The + * freeing is actually happening only once last reference to the mark is + * dropped from a workqueue which first waits for srcu period end. + * + * Caller must have a reference to the mark or be protected by + * fsnotify_mark_srcu. + */ +void fsnotify_free_mark(struct fsnotify_mark *mark) +{ + struct fsnotify_group *group = mark->group; + + spin_lock(&mark->lock); + /* something else already called this function on this mark */ + if (!(mark->flags & FSNOTIFY_MARK_FLAG_ALIVE)) { + spin_unlock(&mark->lock); + return; + } + mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE; + spin_unlock(&mark->lock); + + /* + * Some groups like to know that marks are being freed. This is a + * callback to the group function to let it know that this mark + * is being freed. + */ + if (group->ops->freeing_mark) + group->ops->freeing_mark(mark, group); +} + +void fsnotify_destroy_mark(struct fsnotify_mark *mark, + struct fsnotify_group *group) +{ + fsnotify_group_lock(group); + fsnotify_detach_mark(mark); + fsnotify_group_unlock(group); + fsnotify_free_mark(mark); +} +EXPORT_SYMBOL_GPL(fsnotify_destroy_mark); + +/* + * Sorting function for lists of fsnotify marks. + * + * Fanotify supports different notification classes (reflected as priority of + * notification group). Events shall be passed to notification groups in + * decreasing priority order. To achieve this marks in notification lists for + * inodes and vfsmounts are sorted so that priorities of corresponding groups + * are descending. + * + * Furthermore correct handling of the ignore mask requires processing inode + * and vfsmount marks of each group together. Using the group address as + * further sort criterion provides a unique sorting order and thus we can + * merge inode and vfsmount lists of marks in linear time and find groups + * present in both lists. + * + * A return value of 1 signifies that b has priority over a. + * A return value of 0 signifies that the two marks have to be handled together. + * A return value of -1 signifies that a has priority over b. + */ +int fsnotify_compare_groups(struct fsnotify_group *a, struct fsnotify_group *b) +{ + if (a == b) + return 0; + if (!a) + return 1; + if (!b) + return -1; + if (a->priority < b->priority) + return 1; + if (a->priority > b->priority) + return -1; + if (a < b) + return 1; + return -1; +} + +static int fsnotify_attach_info_to_sb(struct super_block *sb) +{ + struct fsnotify_sb_info *sbinfo; + + /* sb info is freed on fsnotify_sb_delete() */ + sbinfo = kzalloc_obj(*sbinfo); + if (!sbinfo) + return -ENOMEM; + + INIT_LIST_HEAD(&sbinfo->inode_conn_list); + spin_lock_init(&sbinfo->list_lock); + /* + * cmpxchg() provides the barrier so that callers of fsnotify_sb_info() + * will observe an initialized structure + */ + if (cmpxchg(&sb->s_fsnotify_info, NULL, sbinfo)) { + /* Someone else created sbinfo for us */ + kfree(sbinfo); + } + return 0; +} + +struct fsnotify_inode_mark_connector { + struct fsnotify_mark_connector common; + struct list_head conns_list; +}; + +static struct inode *fsnotify_get_living_inode(struct fsnotify_sb_info *sbinfo) +{ + struct fsnotify_inode_mark_connector *iconn; + struct inode *inode; + + spin_lock(&sbinfo->list_lock); + /* Find the first non-evicting inode */ + list_for_each_entry(iconn, &sbinfo->inode_conn_list, conns_list) { + /* All connectors on the list are still attached to an inode */ + inode = iconn->common.obj; + /* + * For connectors without FSNOTIFY_CONN_FLAG_HAS_IREF + * (evictable marks) corresponding inode may well have 0 + * refcount and can be undergoing eviction. OTOH list_lock + * protects us from the connector getting detached and inode + * freed. So we can poke around the inode safely. + */ + spin_lock(&inode->i_lock); + if (likely( + !(inode_state_read(inode) & (I_FREEING | I_WILL_FREE)))) { + __iget(inode); + spin_unlock(&inode->i_lock); + spin_unlock(&sbinfo->list_lock); + return inode; + } + spin_unlock(&inode->i_lock); + } + spin_unlock(&sbinfo->list_lock); + + return NULL; +} + +/** + * fsnotify_unmount_inodes - an sb is unmounting. Handle any watched inodes. + * @sbinfo: fsnotify info for superblock being unmounted. + * + * Walk all inode connectors for the superblock and free all associated marks. + */ +void fsnotify_unmount_inodes(struct fsnotify_sb_info *sbinfo) +{ + struct inode *inode; + + while ((inode = fsnotify_get_living_inode(sbinfo))) { + fsnotify_inode(inode, FS_UNMOUNT); + fsnotify_clear_marks_by_inode(inode); + iput(inode); + cond_resched(); + } +} + +static void fsnotify_init_connector(struct fsnotify_mark_connector *conn, + void *obj, unsigned int obj_type) +{ + spin_lock_init(&conn->lock); + INIT_HLIST_HEAD(&conn->list); + conn->flags = 0; + conn->prio = 0; + conn->type = obj_type; + conn->obj = obj; +} + +static struct fsnotify_mark_connector * +fsnotify_alloc_inode_connector(struct inode *inode) +{ + struct fsnotify_inode_mark_connector *iconn; + struct fsnotify_sb_info *sbinfo = fsnotify_sb_info(inode->i_sb); + + iconn = kmem_cache_alloc(fsnotify_inode_mark_connector_cachep, + GFP_KERNEL); + if (!iconn) + return NULL; + + fsnotify_init_connector(&iconn->common, inode, FSNOTIFY_OBJ_TYPE_INODE); + spin_lock(&sbinfo->list_lock); + list_add(&iconn->conns_list, &sbinfo->inode_conn_list); + spin_unlock(&sbinfo->list_lock); + + return &iconn->common; +} + +static void fsnotify_untrack_connector(struct fsnotify_mark_connector *conn) +{ + struct fsnotify_inode_mark_connector *iconn; + struct fsnotify_sb_info *sbinfo; + + if (conn->type != FSNOTIFY_OBJ_TYPE_INODE) + return; + + iconn = container_of(conn, struct fsnotify_inode_mark_connector, common); + sbinfo = fsnotify_sb_info(fsnotify_conn_inode(conn)->i_sb); + spin_lock(&sbinfo->list_lock); + list_del(&iconn->conns_list); + spin_unlock(&sbinfo->list_lock); +} + +static int fsnotify_attach_connector_to_object(fsnotify_connp_t *connp, + void *obj, unsigned int obj_type) +{ + struct fsnotify_mark_connector *conn; + + if (obj_type == FSNOTIFY_OBJ_TYPE_INODE) { + struct inode *inode = obj; + + conn = fsnotify_alloc_inode_connector(inode); + } else { + conn = kmem_cache_alloc(fsnotify_mark_connector_cachep, + GFP_KERNEL); + if (conn) + fsnotify_init_connector(conn, obj, obj_type); + } + if (!conn) + return -ENOMEM; + + /* + * cmpxchg() provides the barrier so that readers of *connp can see + * only initialized structure + */ + if (cmpxchg(connp, NULL, conn)) { + /* Someone else created list structure for us */ + fsnotify_untrack_connector(conn); + kfree(conn); + } + return 0; +} + +/* + * Get mark connector, make sure it is alive and return with its lock held. + * This is for users that get connector pointer from inode or mount. Users that + * hold reference to a mark on the list may directly lock connector->lock as + * they are sure list cannot go away under them. + */ +static struct fsnotify_mark_connector *fsnotify_grab_connector( + fsnotify_connp_t *connp) +{ + struct fsnotify_mark_connector *conn; + int idx; + + idx = srcu_read_lock(&fsnotify_mark_srcu); + conn = srcu_dereference(*connp, &fsnotify_mark_srcu); + if (!conn) + goto out; + spin_lock(&conn->lock); + if (conn->type == FSNOTIFY_OBJ_TYPE_DETACHED) { + spin_unlock(&conn->lock); + srcu_read_unlock(&fsnotify_mark_srcu, idx); + return NULL; + } +out: + srcu_read_unlock(&fsnotify_mark_srcu, idx); + return conn; +} + +/* + * Add mark into proper place in given list of marks. These marks may be used + * for the fsnotify backend to determine which event types should be delivered + * to which group and for which inodes. These marks are ordered according to + * priority, highest number first, and then by the group's location in memory. + */ +static int fsnotify_add_mark_list(struct fsnotify_mark *mark, void *obj, + unsigned int obj_type, int add_flags) +{ + struct super_block *sb = fsnotify_object_sb(obj, obj_type); + struct fsnotify_mark *lmark, *last = NULL; + struct fsnotify_mark_connector *conn; + fsnotify_connp_t *connp; + int cmp; + int err = 0; + + if (WARN_ON(!fsnotify_valid_obj_type(obj_type))) + return -EINVAL; + + /* + * Attach the sb info before attaching a connector to any object on sb. + * The sb info will remain attached as long as sb lives. + */ + if (sb && !fsnotify_sb_info(sb)) { + err = fsnotify_attach_info_to_sb(sb); + if (err) + return err; + } + + connp = fsnotify_object_connp(obj, obj_type); +restart: + spin_lock(&mark->lock); + conn = fsnotify_grab_connector(connp); + if (!conn) { + spin_unlock(&mark->lock); + err = fsnotify_attach_connector_to_object(connp, obj, obj_type); + if (err) + return err; + goto restart; + } + + /* is mark the first mark? */ + if (hlist_empty(&conn->list)) { + hlist_add_head_rcu(&mark->obj_list, &conn->list); + goto added; + } + + /* should mark be in the middle of the current list? */ + hlist_for_each_entry(lmark, &conn->list, obj_list) { + last = lmark; + + if ((lmark->group == mark->group) && + (lmark->flags & FSNOTIFY_MARK_FLAG_ATTACHED) && + !(mark->group->flags & FSNOTIFY_GROUP_DUPS)) { + err = -EEXIST; + goto out_err; + } + + cmp = fsnotify_compare_groups(lmark->group, mark->group); + if (cmp >= 0) { + hlist_add_before_rcu(&mark->obj_list, &lmark->obj_list); + goto added; + } + } + + BUG_ON(last == NULL); + /* mark should be the last entry. last is the current last entry */ + hlist_add_behind_rcu(&mark->obj_list, &last->obj_list); +added: + if (sb) + fsnotify_update_sb_watchers(sb, conn); + /* + * Since connector is attached to object using cmpxchg() we are + * guaranteed that connector initialization is fully visible by anyone + * seeing mark->connector set. + */ + WRITE_ONCE(mark->connector, conn); +out_err: + spin_unlock(&conn->lock); + spin_unlock(&mark->lock); + return err; +} + +/* + * Attach an initialized mark to a given group and fs object. + * These marks may be used for the fsnotify backend to determine which + * event types should be delivered to which group. + */ +int fsnotify_add_mark_locked(struct fsnotify_mark *mark, + void *obj, unsigned int obj_type, + int add_flags) +{ + struct fsnotify_group *group = mark->group; + int ret = 0; + + fsnotify_group_assert_locked(group); + + /* + * LOCKING ORDER!!!! + * group->mark_mutex + * mark->lock + * mark->connector->lock + */ + spin_lock(&mark->lock); + mark->flags |= FSNOTIFY_MARK_FLAG_ALIVE | FSNOTIFY_MARK_FLAG_ATTACHED; + + list_add(&mark->g_list, &group->marks_list); + fsnotify_get_mark(mark); /* for g_list */ + spin_unlock(&mark->lock); + + ret = fsnotify_add_mark_list(mark, obj, obj_type, add_flags); + if (ret) + goto err; + + fsnotify_recalc_mask(mark->connector); + + return ret; +err: + spin_lock(&mark->lock); + mark->flags &= ~(FSNOTIFY_MARK_FLAG_ALIVE | + FSNOTIFY_MARK_FLAG_ATTACHED); + list_del_init(&mark->g_list); + spin_unlock(&mark->lock); + + fsnotify_put_mark(mark); + return ret; +} + +int fsnotify_add_mark(struct fsnotify_mark *mark, void *obj, + unsigned int obj_type, int add_flags) +{ + int ret; + struct fsnotify_group *group = mark->group; + + fsnotify_group_lock(group); + ret = fsnotify_add_mark_locked(mark, obj, obj_type, add_flags); + fsnotify_group_unlock(group); + return ret; +} +EXPORT_SYMBOL_GPL(fsnotify_add_mark); + +/* + * Given a list of marks, find the mark associated with given group. If found + * take a reference to that mark and return it, else return NULL. + */ +struct fsnotify_mark *fsnotify_find_mark(void *obj, unsigned int obj_type, + struct fsnotify_group *group) +{ + fsnotify_connp_t *connp = fsnotify_object_connp(obj, obj_type); + struct fsnotify_mark_connector *conn; + struct fsnotify_mark *mark; + + if (!connp) + return NULL; + + conn = fsnotify_grab_connector(connp); + if (!conn) + return NULL; + + hlist_for_each_entry(mark, &conn->list, obj_list) { + if (mark->group == group && + (mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) { + fsnotify_get_mark(mark); + spin_unlock(&conn->lock); + return mark; + } + } + spin_unlock(&conn->lock); + return NULL; +} +EXPORT_SYMBOL_GPL(fsnotify_find_mark); + +/* Clear any marks in a group with given type mask */ +void fsnotify_clear_marks_by_group(struct fsnotify_group *group, + unsigned int obj_type) +{ + struct fsnotify_mark *lmark, *mark; + LIST_HEAD(to_free); + struct list_head *head = &to_free; + + /* Skip selection step if we want to clear all marks. */ + if (obj_type == FSNOTIFY_OBJ_TYPE_ANY) { + head = &group->marks_list; + goto clear; + } + /* + * We have to be really careful here. Anytime we drop mark_mutex, e.g. + * fsnotify_clear_marks_by_inode() can come and free marks. Even in our + * to_free list so we have to use mark_mutex even when accessing that + * list. And freeing mark requires us to drop mark_mutex. So we can + * reliably free only the first mark in the list. That's why we first + * move marks to free to to_free list in one go and then free marks in + * to_free list one by one. + */ + fsnotify_group_lock(group); + list_for_each_entry_safe(mark, lmark, &group->marks_list, g_list) { + if (mark->connector->type == obj_type) + list_move(&mark->g_list, &to_free); + } + fsnotify_group_unlock(group); + +clear: + while (1) { + fsnotify_group_lock(group); + if (list_empty(head)) { + fsnotify_group_unlock(group); + break; + } + mark = list_first_entry(head, struct fsnotify_mark, g_list); + fsnotify_get_mark(mark); + fsnotify_detach_mark(mark); + fsnotify_group_unlock(group); + fsnotify_free_mark(mark); + fsnotify_put_mark(mark); + } +} + +/* Destroy all marks attached to an object via connector */ +void fsnotify_destroy_marks(fsnotify_connp_t *connp) +{ + struct fsnotify_mark_connector *conn; + struct fsnotify_mark *mark, *old_mark = NULL; + void *objp; + unsigned int type; + + conn = fsnotify_grab_connector(connp); + if (!conn) + return; + /* + * We have to be careful since we can race with e.g. + * fsnotify_clear_marks_by_group() and once we drop the conn->lock, the + * list can get modified. However we are holding mark reference and + * thus our mark cannot be removed from obj_list so we can continue + * iteration after regaining conn->lock. + */ + hlist_for_each_entry(mark, &conn->list, obj_list) { + fsnotify_get_mark(mark); + spin_unlock(&conn->lock); + if (old_mark) + fsnotify_put_mark(old_mark); + old_mark = mark; + fsnotify_destroy_mark(mark, mark->group); + spin_lock(&conn->lock); + } + /* + * Detach list from object now so that we don't pin inode until all + * mark references get dropped. It would lead to strange results such + * as delaying inode deletion or blocking unmount. + */ + objp = fsnotify_detach_connector_from_object(conn, &type); + spin_unlock(&conn->lock); + if (old_mark) + fsnotify_put_mark(old_mark); + fsnotify_drop_object(type, objp); +} + +/* + * Nothing fancy, just initialize lists and locks and counters. + */ +void fsnotify_init_mark(struct fsnotify_mark *mark, + struct fsnotify_group *group) +{ + memset(mark, 0, sizeof(*mark)); + spin_lock_init(&mark->lock); + refcount_set(&mark->refcnt, 1); + fsnotify_get_group(group); + mark->group = group; + WRITE_ONCE(mark->connector, NULL); +} +EXPORT_SYMBOL_GPL(fsnotify_init_mark); + +/* + * Destroy all marks in destroy_list, waits for SRCU period to finish before + * actually freeing marks. + */ +static void fsnotify_mark_destroy_workfn(struct work_struct *work) +{ + struct fsnotify_mark *mark, *next; + struct list_head private_destroy_list; + + spin_lock(&destroy_lock); + /* exchange the list head */ + list_replace_init(&destroy_list, &private_destroy_list); + spin_unlock(&destroy_lock); + + synchronize_srcu(&fsnotify_mark_srcu); + + list_for_each_entry_safe(mark, next, &private_destroy_list, g_list) { + list_del_init(&mark->g_list); + fsnotify_final_mark_destroy(mark); + } +} + +/* Wait for all marks queued for destruction to be actually destroyed */ +void fsnotify_wait_marks_destroyed(void) +{ + flush_delayed_work(&reaper_work); +} +EXPORT_SYMBOL_GPL(fsnotify_wait_marks_destroyed); + +__init void fsnotify_init_connector_caches(void) +{ + fsnotify_mark_connector_cachep = KMEM_CACHE(fsnotify_mark_connector, + SLAB_PANIC); + fsnotify_inode_mark_connector_cachep = KMEM_CACHE( + fsnotify_inode_mark_connector, + SLAB_PANIC); +} |