| /* |
| * 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: |
| * |
| * mark->lock |
| * group->mark_lock |
| * inode->i_lock |
| * |
| * mark->lock protects 2 things, mark->group and mark->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 marks_list anchored inside a given group |
| * and each mark 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_marks list anchored inside a |
| * given inode and each mark 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) |
| * - 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_marks 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 *mark) |
| { |
| atomic_inc(&mark->refcnt); |
| } |
| |
| void fsnotify_put_mark(struct fsnotify_mark *mark) |
| { |
| if (atomic_dec_and_test(&mark->refcnt)) |
| mark->free_mark(mark); |
| } |
| |
| /* |
| * 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 mark->lock |
| */ |
| void fsnotify_destroy_mark(struct fsnotify_mark *mark) |
| { |
| struct fsnotify_group *group; |
| struct inode *inode = NULL; |
| |
| spin_lock(&mark->lock); |
| |
| group = mark->group; |
| |
| /* if !group something else already marked this to die */ |
| if (!group) { |
| spin_unlock(&mark->lock); |
| return; |
| } |
| |
| /* 1 from caller and 1 for being on i_list/g_list */ |
| BUG_ON(atomic_read(&mark->refcnt) < 2); |
| |
| spin_lock(&group->mark_lock); |
| |
| if (mark->flags & FSNOTIFY_MARK_FLAG_INODE) { |
| fsnotify_destroy_inode_mark(mark); |
| inode = mark->i.inode; |
| } else if (mark->flags & FSNOTIFY_MARK_FLAG_VFSMOUNT) |
| fsnotify_destroy_vfsmount_mark(mark); |
| else |
| BUG(); |
| |
| list_del_init(&mark->g_list); |
| mark->group = NULL; |
| |
| fsnotify_put_mark(mark); /* for i_list and g_list */ |
| |
| spin_unlock(&group->mark_lock); |
| 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); |
| |
| /* |
| * __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 mark->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...) |
| */ |
| |
| if (inode) |
| 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); |
| } |
| |
| /* |
| * 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(struct fsnotify_mark *mark, |
| struct fsnotify_group *group, struct inode *inode, |
| struct vfsmount *mnt, int allow_dups) |
| { |
| int ret = 0; |
| |
| BUG_ON(inode && mnt); |
| BUG_ON(!inode && !mnt); |
| |
| /* |
| * if this group isn't being testing for inode type events we need |
| * to start testing |
| */ |
| if (inode && unlikely(list_empty(&group->inode_group_list))) |
| fsnotify_add_inode_group(group); |
| else if (mnt && unlikely(list_empty(&group->vfsmount_group_list))) |
| fsnotify_add_vfsmount_group(group); |
| |
| /* |
| * LOCKING ORDER!!!! |
| * mark->lock |
| * group->mark_lock |
| * inode->i_lock |
| */ |
| spin_lock(&mark->lock); |
| spin_lock(&group->mark_lock); |
| |
| mark->group = group; |
| list_add(&mark->g_list, &group->marks_list); |
| atomic_inc(&group->num_marks); |
| fsnotify_get_mark(mark); /* for i_list and g_list */ |
| |
| if (inode) { |
| ret = fsnotify_add_inode_mark(mark, group, inode, allow_dups); |
| if (ret) |
| goto err; |
| } else if (mnt) { |
| ret = fsnotify_add_vfsmount_mark(mark, group, mnt, allow_dups); |
| if (ret) |
| goto err; |
| } else { |
| BUG(); |
| } |
| |
| spin_unlock(&group->mark_lock); |
| spin_unlock(&mark->lock); |
| |
| if (inode) |
| __fsnotify_update_child_dentry_flags(inode); |
| |
| return ret; |
| err: |
| mark->group = NULL; |
| list_del_init(&mark->g_list); |
| atomic_dec(&group->num_marks); |
| fsnotify_put_mark(mark); |
| |
| spin_unlock(&group->mark_lock); |
| spin_unlock(&mark->lock); |
| |
| return ret; |
| } |
| |
| /* |
| * 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 *lmark, *mark; |
| LIST_HEAD(free_list); |
| |
| spin_lock(&group->mark_lock); |
| list_for_each_entry_safe(mark, lmark, &group->marks_list, g_list) { |
| list_add(&mark->free_g_list, &free_list); |
| list_del_init(&mark->g_list); |
| fsnotify_get_mark(mark); |
| } |
| spin_unlock(&group->mark_lock); |
| |
| list_for_each_entry_safe(mark, lmark, &free_list, free_g_list) { |
| fsnotify_destroy_mark(mark); |
| fsnotify_put_mark(mark); |
| } |
| } |
| |
| void fsnotify_duplicate_mark(struct fsnotify_mark *new, struct fsnotify_mark *old) |
| { |
| assert_spin_locked(&old->lock); |
| new->i.inode = old->i.inode; |
| new->m.mnt = old->m.mnt; |
| new->group = old->group; |
| new->mask = old->mask; |
| new->free_mark = old->free_mark; |
| } |
| |
| /* |
| * Nothing fancy, just initialize lists and locks and counters. |
| */ |
| void fsnotify_init_mark(struct fsnotify_mark *mark, |
| void (*free_mark)(struct fsnotify_mark *mark)) |
| { |
| memset(mark, 0, sizeof(*mark)); |
| spin_lock_init(&mark->lock); |
| atomic_set(&mark->refcnt, 1); |
| mark->free_mark = free_mark; |
| } |