/*
* 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 <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.
*/
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...)
*/
/*
* 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;
/*
* 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;
fsnotify_put_mark(lentry);
} else {
__fsnotify_update_child_dentry_flags(inode);
}
return ret;
}
