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Diffstat (limited to 'fs/notify/mark.c')
| -rw-r--r-- | fs/notify/mark.c | 294 |
1 files changed, 294 insertions, 0 deletions
diff --git a/fs/notify/mark.c b/fs/notify/mark.c new file mode 100644 index 000000000000..e56e8768d676 --- /dev/null +++ b/fs/notify/mark.c @@ -0,0 +1,294 @@ +/* + * 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; + + spin_lock(&mark->lock); + + group = mark->group; + inode = mark->i.inode; + + BUG_ON(group && !inode); + BUG_ON(!group && inode); + + /* 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); + 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...) + */ + + + 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(mnt); + 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 { + 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)) +{ + spin_lock_init(&mark->lock); + atomic_set(&mark->refcnt, 1); + INIT_HLIST_NODE(&mark->i.i_list); + mark->group = NULL; + mark->mask = 0; + mark->i.inode = NULL; + mark->free_mark = free_mark; +} |