![Jan Kara](/assets/img/avatar_default.png)
Detaching of mark connector from fsnotify_put_mark() can race with
unmounting of the filesystem like:
CPU1 CPU2
fsnotify_put_mark()
spin_lock(&conn->lock);
...
inode = fsnotify_detach_connector_from_object(conn)
spin_unlock(&conn->lock);
generic_shutdown_super()
fsnotify_unmount_inodes()
sees connector detached for inode
-> nothing to do
evict_inode()
barfs on pending inode reference
iput(inode);
Resulting in "Busy inodes after unmount" message and possible kernel
oops. Make fsnotify_unmount_inodes() properly wait for outstanding inode
references from detached connectors.
Note that the accounting of outstanding inode references in the
superblock can cause some cacheline contention on the counter. OTOH it
happens only during deletion of the last notification mark from an inode
(or during unlinking of watched inode) and that is not too bad. I have
measured time to create & delete inotify watch 100000 times from 64
processes in parallel (each process having its own inotify group and its
own file on a shared superblock) on a 64 CPU machine. Average and
standard deviation of 15 runs look like:
Avg Stddev
Vanilla 9.817400 0.276165
Fixed 9.710467 0.228294
So there's no statistically significant difference.
Fixes: 6b3f05d24d
("fsnotify: Detach mark from object list when last reference is dropped")
CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
413 lines
12 KiB
C
413 lines
12 KiB
C
/*
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* Copyright (C) 2008 Red Hat, Inc., Eric Paris <eparis@redhat.com>
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*
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* This program is free software; you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation; either version 2, or (at your option)
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* any later version.
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*
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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program; see the file COPYING. If not, write to
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* the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
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*/
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#include <linux/dcache.h>
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#include <linux/fs.h>
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#include <linux/gfp.h>
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#include <linux/init.h>
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#include <linux/module.h>
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#include <linux/mount.h>
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#include <linux/srcu.h>
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#include <linux/fsnotify_backend.h>
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#include "fsnotify.h"
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/*
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* Clear all of the marks on an inode when it is being evicted from core
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*/
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void __fsnotify_inode_delete(struct inode *inode)
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{
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fsnotify_clear_marks_by_inode(inode);
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}
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EXPORT_SYMBOL_GPL(__fsnotify_inode_delete);
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void __fsnotify_vfsmount_delete(struct vfsmount *mnt)
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{
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fsnotify_clear_marks_by_mount(mnt);
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}
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/**
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* fsnotify_unmount_inodes - an sb is unmounting. handle any watched inodes.
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* @sb: superblock being unmounted.
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*
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* Called during unmount with no locks held, so needs to be safe against
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* concurrent modifiers. We temporarily drop sb->s_inode_list_lock and CAN block.
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*/
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static void fsnotify_unmount_inodes(struct super_block *sb)
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{
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struct inode *inode, *iput_inode = NULL;
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spin_lock(&sb->s_inode_list_lock);
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list_for_each_entry(inode, &sb->s_inodes, i_sb_list) {
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/*
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* We cannot __iget() an inode in state I_FREEING,
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* I_WILL_FREE, or I_NEW which is fine because by that point
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* the inode cannot have any associated watches.
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*/
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spin_lock(&inode->i_lock);
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if (inode->i_state & (I_FREEING|I_WILL_FREE|I_NEW)) {
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spin_unlock(&inode->i_lock);
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continue;
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}
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/*
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* If i_count is zero, the inode cannot have any watches and
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* doing an __iget/iput with SB_ACTIVE clear would actually
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* evict all inodes with zero i_count from icache which is
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* unnecessarily violent and may in fact be illegal to do.
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*/
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if (!atomic_read(&inode->i_count)) {
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spin_unlock(&inode->i_lock);
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continue;
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}
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__iget(inode);
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spin_unlock(&inode->i_lock);
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spin_unlock(&sb->s_inode_list_lock);
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if (iput_inode)
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iput(iput_inode);
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/* for each watch, send FS_UNMOUNT and then remove it */
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fsnotify(inode, FS_UNMOUNT, inode, FSNOTIFY_EVENT_INODE, NULL, 0);
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fsnotify_inode_delete(inode);
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iput_inode = inode;
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spin_lock(&sb->s_inode_list_lock);
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}
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spin_unlock(&sb->s_inode_list_lock);
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if (iput_inode)
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iput(iput_inode);
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/* Wait for outstanding inode references from connectors */
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wait_var_event(&sb->s_fsnotify_inode_refs,
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!atomic_long_read(&sb->s_fsnotify_inode_refs));
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}
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void fsnotify_sb_delete(struct super_block *sb)
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{
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fsnotify_unmount_inodes(sb);
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fsnotify_clear_marks_by_sb(sb);
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}
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/*
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* Given an inode, first check if we care what happens to our children. Inotify
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* and dnotify both tell their parents about events. If we care about any event
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* on a child we run all of our children and set a dentry flag saying that the
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* parent cares. Thus when an event happens on a child it can quickly tell if
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* if there is a need to find a parent and send the event to the parent.
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*/
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void __fsnotify_update_child_dentry_flags(struct inode *inode)
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{
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struct dentry *alias;
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int watched;
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if (!S_ISDIR(inode->i_mode))
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return;
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/* determine if the children should tell inode about their events */
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watched = fsnotify_inode_watches_children(inode);
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spin_lock(&inode->i_lock);
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/* run all of the dentries associated with this inode. Since this is a
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* directory, there damn well better only be one item on this list */
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hlist_for_each_entry(alias, &inode->i_dentry, d_u.d_alias) {
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struct dentry *child;
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/* run all of the children of the original inode and fix their
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* d_flags to indicate parental interest (their parent is the
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* original inode) */
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spin_lock(&alias->d_lock);
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list_for_each_entry(child, &alias->d_subdirs, d_child) {
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if (!child->d_inode)
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continue;
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spin_lock_nested(&child->d_lock, DENTRY_D_LOCK_NESTED);
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if (watched)
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child->d_flags |= DCACHE_FSNOTIFY_PARENT_WATCHED;
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else
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child->d_flags &= ~DCACHE_FSNOTIFY_PARENT_WATCHED;
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spin_unlock(&child->d_lock);
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}
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spin_unlock(&alias->d_lock);
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}
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spin_unlock(&inode->i_lock);
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}
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/* Notify this dentry's parent about a child's events. */
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int __fsnotify_parent(const struct path *path, struct dentry *dentry, __u32 mask)
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{
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struct dentry *parent;
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struct inode *p_inode;
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int ret = 0;
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if (!dentry)
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dentry = path->dentry;
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if (!(dentry->d_flags & DCACHE_FSNOTIFY_PARENT_WATCHED))
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return 0;
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parent = dget_parent(dentry);
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p_inode = parent->d_inode;
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if (unlikely(!fsnotify_inode_watches_children(p_inode)))
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__fsnotify_update_child_dentry_flags(p_inode);
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else if (p_inode->i_fsnotify_mask & mask) {
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struct name_snapshot name;
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/* we are notifying a parent so come up with the new mask which
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* specifies these are events which came from a child. */
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mask |= FS_EVENT_ON_CHILD;
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take_dentry_name_snapshot(&name, dentry);
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if (path)
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ret = fsnotify(p_inode, mask, path, FSNOTIFY_EVENT_PATH,
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name.name, 0);
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else
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ret = fsnotify(p_inode, mask, dentry->d_inode, FSNOTIFY_EVENT_INODE,
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name.name, 0);
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release_dentry_name_snapshot(&name);
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}
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dput(parent);
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return ret;
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}
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EXPORT_SYMBOL_GPL(__fsnotify_parent);
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static int send_to_group(struct inode *to_tell,
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__u32 mask, const void *data,
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int data_is, u32 cookie,
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const unsigned char *file_name,
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struct fsnotify_iter_info *iter_info)
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{
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struct fsnotify_group *group = NULL;
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__u32 test_mask = (mask & ALL_FSNOTIFY_EVENTS);
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__u32 marks_mask = 0;
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__u32 marks_ignored_mask = 0;
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struct fsnotify_mark *mark;
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int type;
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if (WARN_ON(!iter_info->report_mask))
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return 0;
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/* clear ignored on inode modification */
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if (mask & FS_MODIFY) {
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fsnotify_foreach_obj_type(type) {
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if (!fsnotify_iter_should_report_type(iter_info, type))
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continue;
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mark = iter_info->marks[type];
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if (mark &&
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!(mark->flags & FSNOTIFY_MARK_FLAG_IGNORED_SURV_MODIFY))
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mark->ignored_mask = 0;
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}
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}
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fsnotify_foreach_obj_type(type) {
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if (!fsnotify_iter_should_report_type(iter_info, type))
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continue;
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mark = iter_info->marks[type];
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/* does the object mark tell us to do something? */
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if (mark) {
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group = mark->group;
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marks_mask |= mark->mask;
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marks_ignored_mask |= mark->ignored_mask;
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}
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}
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pr_debug("%s: group=%p to_tell=%p mask=%x marks_mask=%x marks_ignored_mask=%x"
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" data=%p data_is=%d cookie=%d\n",
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__func__, group, to_tell, mask, marks_mask, marks_ignored_mask,
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data, data_is, cookie);
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if (!(test_mask & marks_mask & ~marks_ignored_mask))
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return 0;
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return group->ops->handle_event(group, to_tell, mask, data, data_is,
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file_name, cookie, iter_info);
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}
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static struct fsnotify_mark *fsnotify_first_mark(struct fsnotify_mark_connector **connp)
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{
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struct fsnotify_mark_connector *conn;
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struct hlist_node *node = NULL;
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conn = srcu_dereference(*connp, &fsnotify_mark_srcu);
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if (conn)
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node = srcu_dereference(conn->list.first, &fsnotify_mark_srcu);
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return hlist_entry_safe(node, struct fsnotify_mark, obj_list);
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}
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static struct fsnotify_mark *fsnotify_next_mark(struct fsnotify_mark *mark)
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{
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struct hlist_node *node = NULL;
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if (mark)
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node = srcu_dereference(mark->obj_list.next,
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&fsnotify_mark_srcu);
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return hlist_entry_safe(node, struct fsnotify_mark, obj_list);
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}
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/*
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* iter_info is a multi head priority queue of marks.
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* Pick a subset of marks from queue heads, all with the
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* same group and set the report_mask for selected subset.
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* Returns the report_mask of the selected subset.
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*/
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static unsigned int fsnotify_iter_select_report_types(
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struct fsnotify_iter_info *iter_info)
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{
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struct fsnotify_group *max_prio_group = NULL;
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struct fsnotify_mark *mark;
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int type;
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/* Choose max prio group among groups of all queue heads */
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fsnotify_foreach_obj_type(type) {
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mark = iter_info->marks[type];
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if (mark &&
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fsnotify_compare_groups(max_prio_group, mark->group) > 0)
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max_prio_group = mark->group;
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}
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if (!max_prio_group)
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return 0;
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/* Set the report mask for marks from same group as max prio group */
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iter_info->report_mask = 0;
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fsnotify_foreach_obj_type(type) {
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mark = iter_info->marks[type];
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if (mark &&
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fsnotify_compare_groups(max_prio_group, mark->group) == 0)
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fsnotify_iter_set_report_type(iter_info, type);
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}
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return iter_info->report_mask;
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}
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/*
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* Pop from iter_info multi head queue, the marks that were iterated in the
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* current iteration step.
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*/
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static void fsnotify_iter_next(struct fsnotify_iter_info *iter_info)
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{
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int type;
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fsnotify_foreach_obj_type(type) {
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if (fsnotify_iter_should_report_type(iter_info, type))
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iter_info->marks[type] =
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fsnotify_next_mark(iter_info->marks[type]);
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}
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}
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/*
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* This is the main call to fsnotify. The VFS calls into hook specific functions
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* in linux/fsnotify.h. Those functions then in turn call here. Here will call
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* out to all of the registered fsnotify_group. Those groups can then use the
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* notification event in whatever means they feel necessary.
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*/
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int fsnotify(struct inode *to_tell, __u32 mask, const void *data, int data_is,
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const unsigned char *file_name, u32 cookie)
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{
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struct fsnotify_iter_info iter_info = {};
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struct super_block *sb = NULL;
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struct mount *mnt = NULL;
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__u32 mnt_or_sb_mask = 0;
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int ret = 0;
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__u32 test_mask = (mask & ALL_FSNOTIFY_EVENTS);
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if (data_is == FSNOTIFY_EVENT_PATH) {
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mnt = real_mount(((const struct path *)data)->mnt);
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sb = mnt->mnt.mnt_sb;
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mnt_or_sb_mask = mnt->mnt_fsnotify_mask | sb->s_fsnotify_mask;
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}
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/*
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* Optimization: srcu_read_lock() has a memory barrier which can
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* be expensive. It protects walking the *_fsnotify_marks lists.
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* However, if we do not walk the lists, we do not have to do
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* SRCU because we have no references to any objects and do not
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* need SRCU to keep them "alive".
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*/
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if (!to_tell->i_fsnotify_marks &&
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(!mnt || (!mnt->mnt_fsnotify_marks && !sb->s_fsnotify_marks)))
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return 0;
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/*
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* if this is a modify event we may need to clear the ignored masks
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* otherwise return if neither the inode nor the vfsmount/sb care about
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* this type of event.
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*/
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if (!(mask & FS_MODIFY) &&
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!(test_mask & (to_tell->i_fsnotify_mask | mnt_or_sb_mask)))
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return 0;
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iter_info.srcu_idx = srcu_read_lock(&fsnotify_mark_srcu);
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iter_info.marks[FSNOTIFY_OBJ_TYPE_INODE] =
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fsnotify_first_mark(&to_tell->i_fsnotify_marks);
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if (mnt) {
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iter_info.marks[FSNOTIFY_OBJ_TYPE_VFSMOUNT] =
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fsnotify_first_mark(&mnt->mnt_fsnotify_marks);
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iter_info.marks[FSNOTIFY_OBJ_TYPE_SB] =
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fsnotify_first_mark(&sb->s_fsnotify_marks);
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}
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/*
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* We need to merge inode/vfsmount/sb mark lists so that e.g. inode mark
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* ignore masks are properly reflected for mount/sb mark notifications.
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* That's why this traversal is so complicated...
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*/
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while (fsnotify_iter_select_report_types(&iter_info)) {
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ret = send_to_group(to_tell, mask, data, data_is, cookie,
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file_name, &iter_info);
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if (ret && (mask & ALL_FSNOTIFY_PERM_EVENTS))
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goto out;
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fsnotify_iter_next(&iter_info);
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}
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ret = 0;
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out:
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srcu_read_unlock(&fsnotify_mark_srcu, iter_info.srcu_idx);
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return ret;
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}
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EXPORT_SYMBOL_GPL(fsnotify);
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extern struct kmem_cache *fsnotify_mark_connector_cachep;
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static __init int fsnotify_init(void)
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{
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int ret;
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BUILD_BUG_ON(HWEIGHT32(ALL_FSNOTIFY_BITS) != 23);
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ret = init_srcu_struct(&fsnotify_mark_srcu);
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if (ret)
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panic("initializing fsnotify_mark_srcu");
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fsnotify_mark_connector_cachep = KMEM_CACHE(fsnotify_mark_connector,
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SLAB_PANIC);
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return 0;
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}
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core_initcall(fsnotify_init);
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