/* * Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com> * * This program is free software; you can redistribute it and/or modify * it under the terms of the GNU General Public License as published by * the Free Software Foundation; either version 2, or (at your option) * any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program; see the file COPYING. If not, write to * the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA. */ /* * fsnotify inode mark locking/lifetime/and refcnting * * REFCNT: * The mark->refcnt tells how many "things" in the kernel currently are * referencing this object. The object typically will live inside the kernel * with a refcnt of 2, one for each list it is on (i_list, g_list). Any task * which can find this object holding the appropriete locks, can take a reference * and the object itself is guarenteed to survive until the reference is dropped. * * LOCKING: * There are 3 spinlocks involved with fsnotify inode marks and they MUST * be taken in order as follows: * * entry->lock * group->mark_lock * inode->i_lock * * entry->lock protects 2 things, entry->group and entry->inode. You must hold * that lock to dereference either of these things (they could be NULL even with * the lock) * * group->mark_lock protects the mark_entries list anchored inside a given group * and each entry is hooked via the g_list. It also sorta protects the * free_g_list, which when used is anchored by a private list on the stack of the * task which held the group->mark_lock. * * inode->i_lock protects the i_fsnotify_mark_entries list anchored inside a * given inode and each entry is hooked via the i_list. (and sorta the * free_i_list) * * * LIFETIME: * Inode marks survive between when they are added to an inode and when their * refcnt==0. * * 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_by_entry) * - The fsnotify_group associated with the mark is going away and all such marks * need to be cleaned up. (fsnotify_clear_marks_by_group) * * Worst case we are given an inode and need to clean up all the marks on that * inode. We take i_lock and walk the i_fsnotify_mark_entries safely. For each * mark on the list we take a reference (so the mark can't disappear under us). * We remove that mark form the inode's list of marks and we add this mark to a * private list anchored on the stack using i_free_list; At this point we no * longer fear anything finding the mark using the inode's list of marks. * * We can safely and locklessly run the private list on the stack of everything * we just unattached from the original inode. For each mark on the private list * we grab the mark-> and can thus dereference mark->group and mark->inode. If * we see the group and inode are not NULL we take those locks. Now holding all * 3 locks we can completely remove the mark from other tasks finding it in the * future. Remember, 10 things might already be referencing this mark, but they * better be holding a ref. We drop our reference we took before we unhooked it * from the inode. When the ref hits 0 we can free the mark. * * Very similarly for freeing by group, except we use free_g_list. * * 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/module.h> #include <linux/mutex.h> #include <linux/slab.h> #include <linux/spinlock.h> #include <linux/writeback.h> /* for inode_lock */ #include <asm/atomic.h> #include <linux/fsnotify_backend.h> #include "fsnotify.h" void fsnotify_get_mark(struct fsnotify_mark_entry *entry) { atomic_inc(&entry->refcnt); } void fsnotify_put_mark(struct fsnotify_mark_entry *entry) { if (atomic_dec_and_test(&entry->refcnt)) entry->free_mark(entry); } /* * Recalculate the mask of events relevant to a given inode locked. */ static void fsnotify_recalc_inode_mask_locked(struct inode *inode) { struct fsnotify_mark_entry *entry; struct hlist_node *pos; __u32 new_mask = 0; assert_spin_locked(&inode->i_lock); hlist_for_each_entry(entry, pos, &inode->i_fsnotify_mark_entries, i_list) new_mask |= entry->mask; inode->i_fsnotify_mask = new_mask; } /* * Recalculate the inode->i_fsnotify_mask, or the mask of all FS_* event types * any notifier is interested in hearing for this inode. */ void fsnotify_recalc_inode_mask(struct inode *inode) { spin_lock(&inode->i_lock); fsnotify_recalc_inode_mask_locked(inode); spin_unlock(&inode->i_lock); __fsnotify_update_child_dentry_flags(inode); } /* * Any time a mark is getting freed we end up here. * The caller had better be holding a reference to this mark so we don't actually * do the final put under the entry->lock */ void fsnotify_destroy_mark_by_entry(struct fsnotify_mark_entry *entry) { struct fsnotify_group *group; struct inode *inode; spin_lock(&entry->lock); group = entry->group; inode = entry->inode; BUG_ON(group && !inode); BUG_ON(!group && inode); /* if !group something else already marked this to die */ if (!group) { spin_unlock(&entry->lock); return; } /* 1 from caller and 1 for being on i_list/g_list */ BUG_ON(atomic_read(&entry->refcnt) < 2); spin_lock(&group->mark_lock); spin_lock(&inode->i_lock); hlist_del_init(&entry->i_list); entry->inode = NULL; list_del_init(&entry->g_list); entry->group = NULL; fsnotify_put_mark(entry); /* for i_list and g_list */ /* * this mark is now off the inode->i_fsnotify_mark_entries list and we * hold the inode->i_lock, so this is the perfect time to update the * inode->i_fsnotify_mask */ fsnotify_recalc_inode_mask_locked(inode); spin_unlock(&inode->i_lock); spin_unlock(&group->mark_lock); spin_unlock(&entry->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 entry * is being freed. */ if (group->ops->freeing_mark) group->ops->freeing_mark(entry, group); /* * __fsnotify_update_child_dentry_flags(inode); * * I really want to call that, but we can't, we have no idea if the inode * still exists the second we drop the entry->lock. * * The next time an event arrive to this inode from one of it's children * __fsnotify_parent will see that the inode doesn't care about it's * children and will update all of these flags then. So really this * is just a lazy update (and could be a perf win...) */ iput(inode); /* * it's possible that this group tried to destroy itself, but this * this mark was simultaneously being freed by inode. If that's the * case, we finish freeing the group here. */ if (unlikely(atomic_dec_and_test(&group->num_marks))) fsnotify_final_destroy_group(group); } /* * Given a group, destroy all of the marks associated with that group. */ void fsnotify_clear_marks_by_group(struct fsnotify_group *group) { struct fsnotify_mark_entry *lentry, *entry; LIST_HEAD(free_list); spin_lock(&group->mark_lock); list_for_each_entry_safe(entry, lentry, &group->mark_entries, g_list) { list_add(&entry->free_g_list, &free_list); list_del_init(&entry->g_list); fsnotify_get_mark(entry); } spin_unlock(&group->mark_lock); list_for_each_entry_safe(entry, lentry, &free_list, free_g_list) { fsnotify_destroy_mark_by_entry(entry); fsnotify_put_mark(entry); } } /* * Given an inode, destroy all of the marks associated with that inode. */ void fsnotify_clear_marks_by_inode(struct inode *inode) { struct fsnotify_mark_entry *entry, *lentry; struct hlist_node *pos, *n; LIST_HEAD(free_list); spin_lock(&inode->i_lock); hlist_for_each_entry_safe(entry, pos, n, &inode->i_fsnotify_mark_entries, i_list) { list_add(&entry->free_i_list, &free_list); hlist_del_init(&entry->i_list); fsnotify_get_mark(entry); } spin_unlock(&inode->i_lock); list_for_each_entry_safe(entry, lentry, &free_list, free_i_list) { fsnotify_destroy_mark_by_entry(entry); fsnotify_put_mark(entry); } } /* * given a group and inode, find the mark associated with that combination. * if found take a reference to that mark and return it, else return NULL */ struct fsnotify_mark_entry *fsnotify_find_mark_entry(struct fsnotify_group *group, struct inode *inode) { struct fsnotify_mark_entry *entry; struct hlist_node *pos; assert_spin_locked(&inode->i_lock); hlist_for_each_entry(entry, pos, &inode->i_fsnotify_mark_entries, i_list) { if (entry->group == group) { fsnotify_get_mark(entry); return entry; } } return NULL; } /* * Nothing fancy, just initialize lists and locks and counters. */ void fsnotify_init_mark(struct fsnotify_mark_entry *entry, void (*free_mark)(struct fsnotify_mark_entry *entry)) { spin_lock_init(&entry->lock); atomic_set(&entry->refcnt, 1); INIT_HLIST_NODE(&entry->i_list); entry->group = NULL; entry->mask = 0; entry->inode = NULL; entry->free_mark = free_mark; } /* * Attach an initialized mark entry to a given group and inode. * These marks may be used for the fsnotify backend to determine which * event types should be delivered to which group and for which inodes. */ int fsnotify_add_mark(struct fsnotify_mark_entry *entry, struct fsnotify_group *group, struct inode *inode) { struct fsnotify_mark_entry *lentry; int ret = 0; inode = igrab(inode); if (unlikely(!inode)) return -EINVAL; /* * LOCKING ORDER!!!! * entry->lock * group->mark_lock * inode->i_lock */ spin_lock(&entry->lock); spin_lock(&group->mark_lock); spin_lock(&inode->i_lock); entry->group = group; entry->inode = inode; lentry = fsnotify_find_mark_entry(group, inode); if (!lentry) { hlist_add_head(&entry->i_list, &inode->i_fsnotify_mark_entries); list_add(&entry->g_list, &group->mark_entries); fsnotify_get_mark(entry); /* for i_list and g_list */ atomic_inc(&group->num_marks); fsnotify_recalc_inode_mask_locked(inode); } spin_unlock(&inode->i_lock); spin_unlock(&group->mark_lock); spin_unlock(&entry->lock); if (lentry) { ret = -EEXIST; iput(inode); fsnotify_put_mark(lentry); } else { __fsnotify_update_child_dentry_flags(inode); } return ret; } /** * fsnotify_unmount_inodes - an sb is unmounting. handle any watched inodes. * @list: list of inodes being unmounted (sb->s_inodes) * * Called with inode_lock held, protecting the unmounting super block's list * of inodes, and with iprune_mutex held, keeping shrink_icache_memory() at bay. * We temporarily drop inode_lock, however, and CAN block. */ void fsnotify_unmount_inodes(struct list_head *list) { struct inode *inode, *next_i, *need_iput = NULL; list_for_each_entry_safe(inode, next_i, list, i_sb_list) { struct inode *need_iput_tmp; /* * We cannot __iget() an inode in state I_CLEAR, I_FREEING, * I_WILL_FREE, or I_NEW which is fine because by that point * the inode cannot have any associated watches. */ if (inode->i_state & (I_CLEAR|I_FREEING|I_WILL_FREE|I_NEW)) continue; /* * If i_count is zero, the inode cannot have any watches and * doing an __iget/iput with MS_ACTIVE clear would actually * evict all inodes with zero i_count from icache which is * unnecessarily violent and may in fact be illegal to do. */ if (!atomic_read(&inode->i_count)) continue; need_iput_tmp = need_iput; need_iput = NULL; /* In case fsnotify_inode_delete() drops a reference. */ if (inode != need_iput_tmp) __iget(inode); else need_iput_tmp = NULL; /* In case the dropping of a reference would nuke next_i. */ if ((&next_i->i_sb_list != list) && atomic_read(&next_i->i_count) && !(next_i->i_state & (I_CLEAR | I_FREEING | I_WILL_FREE))) { __iget(next_i); need_iput = next_i; } /* * We can safely drop inode_lock here because we hold * references on both inode and next_i. Also no new inodes * will be added since the umount has begun. Finally, * iprune_mutex keeps shrink_icache_memory() away. */ spin_unlock(&inode_lock); if (need_iput_tmp) iput(need_iput_tmp); /* for each watch, send FS_UNMOUNT and then remove it */ fsnotify(inode, FS_UNMOUNT, inode, FSNOTIFY_EVENT_INODE, NULL, 0); fsnotify_inode_delete(inode); iput(inode); spin_lock(&inode_lock); } }