linux/fs/notify/fsnotify.c
Jan Kara 9dd813c15b fsnotify: Move mark list head from object into dedicated structure
Currently notification marks are attached to object (inode or vfsmnt) by
a hlist_head in the object. The list is also protected by a spinlock in
the object. So while there is any mark attached to the list of marks,
the object must be pinned in memory (and thus e.g. last iput() deleting
inode cannot happen). Also for list iteration in fsnotify() to work, we
must hold fsnotify_mark_srcu lock so that mark itself and
mark->obj_list.next cannot get freed. Thus we are required to wait for
response to fanotify events from userspace process with
fsnotify_mark_srcu lock held. That causes issues when userspace process
is buggy and does not reply to some event - basically the whole
notification subsystem gets eventually stuck.

So to be able to drop fsnotify_mark_srcu lock while waiting for
response, we have to pin the mark in memory and make sure it stays in
the object list (as removing the mark waiting for response could lead to
lost notification events for groups later in the list). However we don't
want inode reclaim to block on such mark as that would lead to system
just locking up elsewhere.

This commit is the first in the series that paves way towards solving
these conflicting lifetime needs. Instead of anchoring the list of marks
directly in the object, we anchor it in a dedicated structure
(fsnotify_mark_connector) and just point to that structure from the
object. The following commits will also add spinlock protecting the list
and object pointer to the structure.

Reviewed-by: Miklos Szeredi <mszeredi@redhat.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
2017-04-10 17:37:34 +02:00

323 lines
9.6 KiB
C

/*
* 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.
*/
#include <linux/dcache.h>
#include <linux/fs.h>
#include <linux/gfp.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/mount.h>
#include <linux/srcu.h>
#include <linux/fsnotify_backend.h>
#include "fsnotify.h"
/*
* Clear all of the marks on an inode when it is being evicted from core
*/
void __fsnotify_inode_delete(struct inode *inode)
{
fsnotify_clear_marks_by_inode(inode);
}
EXPORT_SYMBOL_GPL(__fsnotify_inode_delete);
void __fsnotify_vfsmount_delete(struct vfsmount *mnt)
{
fsnotify_clear_marks_by_mount(mnt);
}
/*
* Given an inode, first check if we care what happens to our children. Inotify
* and dnotify both tell their parents about events. If we care about any event
* on a child we run all of our children and set a dentry flag saying that the
* parent cares. Thus when an event happens on a child it can quickly tell if
* if there is a need to find a parent and send the event to the parent.
*/
void __fsnotify_update_child_dentry_flags(struct inode *inode)
{
struct dentry *alias;
int watched;
if (!S_ISDIR(inode->i_mode))
return;
/* determine if the children should tell inode about their events */
watched = fsnotify_inode_watches_children(inode);
spin_lock(&inode->i_lock);
/* run all of the dentries associated with this inode. Since this is a
* directory, there damn well better only be one item on this list */
hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
struct dentry *child;
/* run all of the children of the original inode and fix their
* d_flags to indicate parental interest (their parent is the
* original inode) */
spin_lock(&alias->d_lock);
list_for_each_entry(child, &alias->d_subdirs, d_child) {
if (!child->d_inode)
continue;
spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED);
if (watched)
child->d_flags |= DCACHE_FSNOTIFY_PARENT_WATCHED;
else
child->d_flags &= ~DCACHE_FSNOTIFY_PARENT_WATCHED;
spin_unlock(&child->d_lock);
}
spin_unlock(&alias->d_lock);
}
spin_unlock(&inode->i_lock);
}
/* Notify this dentry's parent about a child's events. */
int __fsnotify_parent(const struct path *path, struct dentry *dentry, __u32 mask)
{
struct dentry *parent;
struct inode *p_inode;
int ret = 0;
if (!dentry)
dentry = path->dentry;
if (!(dentry->d_flags & DCACHE_FSNOTIFY_PARENT_WATCHED))
return 0;
parent = dget_parent(dentry);
p_inode = parent->d_inode;
if (unlikely(!fsnotify_inode_watches_children(p_inode)))
__fsnotify_update_child_dentry_flags(p_inode);
else if (p_inode->i_fsnotify_mask & mask) {
/* we are notifying a parent so come up with the new mask which
* specifies these are events which came from a child. */
mask |= FS_EVENT_ON_CHILD;
if (path)
ret = fsnotify(p_inode, mask, path, FSNOTIFY_EVENT_PATH,
dentry->d_name.name, 0);
else
ret = fsnotify(p_inode, mask, dentry->d_inode, FSNOTIFY_EVENT_INODE,
dentry->d_name.name, 0);
}
dput(parent);
return ret;
}
EXPORT_SYMBOL_GPL(__fsnotify_parent);
static int send_to_group(struct inode *to_tell,
struct fsnotify_mark *inode_mark,
struct fsnotify_mark *vfsmount_mark,
__u32 mask, const void *data,
int data_is, u32 cookie,
const unsigned char *file_name)
{
struct fsnotify_group *group = NULL;
__u32 inode_test_mask = 0;
__u32 vfsmount_test_mask = 0;
if (unlikely(!inode_mark && !vfsmount_mark)) {
BUG();
return 0;
}
/* clear ignored on inode modification */
if (mask & FS_MODIFY) {
if (inode_mark &&
!(inode_mark->flags & FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY))
inode_mark->ignored_mask = 0;
if (vfsmount_mark &&
!(vfsmount_mark->flags & FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY))
vfsmount_mark->ignored_mask = 0;
}
/* does the inode mark tell us to do something? */
if (inode_mark) {
group = inode_mark->group;
inode_test_mask = (mask & ~FS_EVENT_ON_CHILD);
inode_test_mask &= inode_mark->mask;
inode_test_mask &= ~inode_mark->ignored_mask;
}
/* does the vfsmount_mark tell us to do something? */
if (vfsmount_mark) {
vfsmount_test_mask = (mask & ~FS_EVENT_ON_CHILD);
group = vfsmount_mark->group;
vfsmount_test_mask &= vfsmount_mark->mask;
vfsmount_test_mask &= ~vfsmount_mark->ignored_mask;
if (inode_mark)
vfsmount_test_mask &= ~inode_mark->ignored_mask;
}
pr_debug("%s: group=%p to_tell=%p mask=%x inode_mark=%p"
" inode_test_mask=%x vfsmount_mark=%p vfsmount_test_mask=%x"
" data=%p data_is=%d cookie=%d\n",
__func__, group, to_tell, mask, inode_mark,
inode_test_mask, vfsmount_mark, vfsmount_test_mask, data,
data_is, cookie);
if (!inode_test_mask && !vfsmount_test_mask)
return 0;
return group->ops->handle_event(group, to_tell, inode_mark,
vfsmount_mark, mask, data, data_is,
file_name, cookie);
}
/*
* This is the main call to fsnotify. The VFS calls into hook specific functions
* in linux/fsnotify.h. Those functions then in turn call here. Here will call
* out to all of the registered fsnotify_group. Those groups can then use the
* notification event in whatever means they feel necessary.
*/
int fsnotify(struct inode *to_tell, __u32 mask, const void *data, int data_is,
const unsigned char *file_name, u32 cookie)
{
struct hlist_node *inode_node = NULL, *vfsmount_node = NULL;
struct fsnotify_mark *inode_mark = NULL, *vfsmount_mark = NULL;
struct fsnotify_group *inode_group, *vfsmount_group;
struct fsnotify_mark_connector *inode_conn, *vfsmount_conn;
struct mount *mnt;
int idx, ret = 0;
/* global tests shouldn't care about events on child only the specific event */
__u32 test_mask = (mask & ~FS_EVENT_ON_CHILD);
if (data_is == FSNOTIFY_EVENT_PATH)
mnt = real_mount(((const struct path *)data)->mnt);
else
mnt = NULL;
/*
* Optimization: srcu_read_lock() has a memory barrier which can
* be expensive. It protects walking the *_fsnotify_marks lists.
* However, if we do not walk the lists, we do not have to do
* SRCU because we have no references to any objects and do not
* need SRCU to keep them "alive".
*/
if (!to_tell->i_fsnotify_marks &&
(!mnt || !mnt->mnt_fsnotify_marks))
return 0;
/*
* if this is a modify event we may need to clear the ignored masks
* otherwise return if neither the inode nor the vfsmount care about
* this type of event.
*/
if (!(mask & FS_MODIFY) &&
!(test_mask & to_tell->i_fsnotify_mask) &&
!(mnt && test_mask & mnt->mnt_fsnotify_mask))
return 0;
idx = srcu_read_lock(&fsnotify_mark_srcu);
if ((mask & FS_MODIFY) ||
(test_mask & to_tell->i_fsnotify_mask)) {
inode_conn = lockless_dereference(to_tell->i_fsnotify_marks);
if (inode_conn)
inode_node = srcu_dereference(inode_conn->list.first,
&fsnotify_mark_srcu);
}
if (mnt && ((mask & FS_MODIFY) ||
(test_mask & mnt->mnt_fsnotify_mask))) {
inode_conn = lockless_dereference(to_tell->i_fsnotify_marks);
if (inode_conn)
inode_node = srcu_dereference(inode_conn->list.first,
&fsnotify_mark_srcu);
vfsmount_conn = lockless_dereference(mnt->mnt_fsnotify_marks);
if (vfsmount_conn)
vfsmount_node = srcu_dereference(
vfsmount_conn->list.first,
&fsnotify_mark_srcu);
}
/*
* We need to merge inode & vfsmount mark lists so that inode mark
* ignore masks are properly reflected for mount mark notifications.
* That's why this traversal is so complicated...
*/
while (inode_node || vfsmount_node) {
inode_group = NULL;
inode_mark = NULL;
vfsmount_group = NULL;
vfsmount_mark = NULL;
if (inode_node) {
inode_mark = hlist_entry(srcu_dereference(inode_node, &fsnotify_mark_srcu),
struct fsnotify_mark, obj_list);
inode_group = inode_mark->group;
}
if (vfsmount_node) {
vfsmount_mark = hlist_entry(srcu_dereference(vfsmount_node, &fsnotify_mark_srcu),
struct fsnotify_mark, obj_list);
vfsmount_group = vfsmount_mark->group;
}
if (inode_group && vfsmount_group) {
int cmp = fsnotify_compare_groups(inode_group,
vfsmount_group);
if (cmp > 0) {
inode_group = NULL;
inode_mark = NULL;
} else if (cmp < 0) {
vfsmount_group = NULL;
vfsmount_mark = NULL;
}
}
ret = send_to_group(to_tell, inode_mark, vfsmount_mark, mask,
data, data_is, cookie, file_name);
if (ret && (mask & ALL_FSNOTIFY_PERM_EVENTS))
goto out;
if (inode_group)
inode_node = srcu_dereference(inode_node->next,
&fsnotify_mark_srcu);
if (vfsmount_group)
vfsmount_node = srcu_dereference(vfsmount_node->next,
&fsnotify_mark_srcu);
}
ret = 0;
out:
srcu_read_unlock(&fsnotify_mark_srcu, idx);
return ret;
}
EXPORT_SYMBOL_GPL(fsnotify);
extern struct kmem_cache *fsnotify_mark_connector_cachep;
static __init int fsnotify_init(void)
{
int ret;
BUG_ON(hweight32(ALL_FSNOTIFY_EVENTS) != 23);
ret = init_srcu_struct(&fsnotify_mark_srcu);
if (ret)
panic("initializing fsnotify_mark_srcu");
fsnotify_mark_connector_cachep = KMEM_CACHE(fsnotify_mark_connector,
SLAB_PANIC);
return 0;
}
core_initcall(fsnotify_init);