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![Eric Paris](/assets/img/avatar_default.png)
The global fsnotify groups lists were invented as a way to increase the performance of fsnotify by shortcutting events which were not interesting. With the changes to walk the object lists rather than global groups lists these shortcuts are not useful. Signed-off-by: Eric Paris <eparis@redhat.com>
371 lines
11 KiB
C
371 lines
11 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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/*
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* fsnotify inode mark locking/lifetime/and refcnting
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*
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* REFCNT:
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* The mark->refcnt tells how many "things" in the kernel currently are
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* referencing this object. The object typically will live inside the kernel
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* with a refcnt of 2, one for each list it is on (i_list, g_list). Any task
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* which can find this object holding the appropriete locks, can take a reference
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* and the object itself is guarenteed to survive until the reference is dropped.
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*
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* LOCKING:
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* There are 3 spinlocks involved with fsnotify inode marks and they MUST
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* be taken in order as follows:
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*
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* mark->lock
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* group->mark_lock
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* inode->i_lock
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*
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* mark->lock protects 2 things, mark->group and mark->inode. You must hold
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* that lock to dereference either of these things (they could be NULL even with
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* the lock)
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*
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* group->mark_lock protects the marks_list anchored inside a given group
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* and each mark is hooked via the g_list. It also sorta protects the
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* free_g_list, which when used is anchored by a private list on the stack of the
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* task which held the group->mark_lock.
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*
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* inode->i_lock protects the i_fsnotify_marks list anchored inside a
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* given inode and each mark is hooked via the i_list. (and sorta the
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* free_i_list)
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*
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*
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* LIFETIME:
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* Inode marks survive between when they are added to an inode and when their
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* refcnt==0.
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*
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* The inode mark can be cleared for a number of different reasons including:
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* - The inode is unlinked for the last time. (fsnotify_inode_remove)
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* - The inode is being evicted from cache. (fsnotify_inode_delete)
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* - The fs the inode is on is unmounted. (fsnotify_inode_delete/fsnotify_unmount_inodes)
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* - Something explicitly requests that it be removed. (fsnotify_destroy_mark)
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* - The fsnotify_group associated with the mark is going away and all such marks
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* need to be cleaned up. (fsnotify_clear_marks_by_group)
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*
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* Worst case we are given an inode and need to clean up all the marks on that
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* inode. We take i_lock and walk the i_fsnotify_marks safely. For each
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* mark on the list we take a reference (so the mark can't disappear under us).
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* We remove that mark form the inode's list of marks and we add this mark to a
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* private list anchored on the stack using i_free_list; At this point we no
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* longer fear anything finding the mark using the inode's list of marks.
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*
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* We can safely and locklessly run the private list on the stack of everything
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* we just unattached from the original inode. For each mark on the private list
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* we grab the mark-> and can thus dereference mark->group and mark->inode. If
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* we see the group and inode are not NULL we take those locks. Now holding all
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* 3 locks we can completely remove the mark from other tasks finding it in the
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* future. Remember, 10 things might already be referencing this mark, but they
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* better be holding a ref. We drop our reference we took before we unhooked it
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* from the inode. When the ref hits 0 we can free the mark.
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*
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* Very similarly for freeing by group, except we use free_g_list.
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*
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* This has the very interesting property of being able to run concurrently with
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* any (or all) other directions.
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*/
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#include <linux/fs.h>
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#include <linux/init.h>
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#include <linux/kernel.h>
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#include <linux/kthread.h>
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#include <linux/module.h>
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#include <linux/mutex.h>
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#include <linux/slab.h>
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#include <linux/spinlock.h>
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#include <linux/srcu.h>
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#include <linux/writeback.h> /* for inode_lock */
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#include <asm/atomic.h>
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#include <linux/fsnotify_backend.h>
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#include "fsnotify.h"
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struct srcu_struct fsnotify_mark_srcu;
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static DEFINE_SPINLOCK(destroy_lock);
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static LIST_HEAD(destroy_list);
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static DECLARE_WAIT_QUEUE_HEAD(destroy_waitq);
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void fsnotify_get_mark(struct fsnotify_mark *mark)
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{
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atomic_inc(&mark->refcnt);
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}
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void fsnotify_put_mark(struct fsnotify_mark *mark)
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{
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if (atomic_dec_and_test(&mark->refcnt))
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mark->free_mark(mark);
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}
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/*
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* Any time a mark is getting freed we end up here.
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* The caller had better be holding a reference to this mark so we don't actually
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* do the final put under the mark->lock
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*/
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void fsnotify_destroy_mark(struct fsnotify_mark *mark)
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{
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struct fsnotify_group *group;
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struct inode *inode = NULL;
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spin_lock(&mark->lock);
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group = mark->group;
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/* something else already called this function on this mark */
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if (!(mark->flags & FSNOTIFY_MARK_FLAG_ALIVE)) {
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spin_unlock(&mark->lock);
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return;
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}
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mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE;
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/* 1 from caller and 1 for being on i_list/g_list */
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BUG_ON(atomic_read(&mark->refcnt) < 2);
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spin_lock(&group->mark_lock);
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if (mark->flags & FSNOTIFY_MARK_FLAG_INODE) {
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inode = mark->i.inode;
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fsnotify_destroy_inode_mark(mark);
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} else if (mark->flags & FSNOTIFY_MARK_FLAG_VFSMOUNT)
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fsnotify_destroy_vfsmount_mark(mark);
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else
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BUG();
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list_del_init(&mark->g_list);
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spin_unlock(&group->mark_lock);
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spin_unlock(&mark->lock);
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spin_lock(&destroy_lock);
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list_add(&mark->destroy_list, &destroy_list);
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spin_unlock(&destroy_lock);
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wake_up(&destroy_waitq);
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/*
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* Some groups like to know that marks are being freed. This is a
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* callback to the group function to let it know that this mark
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* is being freed.
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*/
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if (group->ops->freeing_mark)
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group->ops->freeing_mark(mark, group);
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/*
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* __fsnotify_update_child_dentry_flags(inode);
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*
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* I really want to call that, but we can't, we have no idea if the inode
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* still exists the second we drop the mark->lock.
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*
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* The next time an event arrive to this inode from one of it's children
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* __fsnotify_parent will see that the inode doesn't care about it's
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* children and will update all of these flags then. So really this
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* is just a lazy update (and could be a perf win...)
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*/
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if (inode && (mark->flags & FSNOTIFY_MARK_FLAG_OBJECT_PINNED))
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iput(inode);
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/*
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* it's possible that this group tried to destroy itself, but this
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* this mark was simultaneously being freed by inode. If that's the
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* case, we finish freeing the group here.
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*/
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if (unlikely(atomic_dec_and_test(&group->num_marks)))
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fsnotify_final_destroy_group(group);
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}
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void fsnotify_set_mark_mask_locked(struct fsnotify_mark *mark, __u32 mask)
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{
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assert_spin_locked(&mark->lock);
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mark->mask = mask;
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if (mark->flags & FSNOTIFY_MARK_FLAG_INODE)
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fsnotify_set_inode_mark_mask_locked(mark, mask);
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}
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void fsnotify_set_mark_ignored_mask_locked(struct fsnotify_mark *mark, __u32 mask)
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{
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assert_spin_locked(&mark->lock);
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mark->ignored_mask = mask;
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}
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/*
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* Attach an initialized mark to a given group and fs object.
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* These marks may be used for the fsnotify backend to determine which
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* event types should be delivered to which group.
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*/
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int fsnotify_add_mark(struct fsnotify_mark *mark,
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struct fsnotify_group *group, struct inode *inode,
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struct vfsmount *mnt, int allow_dups)
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{
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int ret = 0;
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BUG_ON(inode && mnt);
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BUG_ON(!inode && !mnt);
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/*
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* LOCKING ORDER!!!!
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* mark->lock
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* group->mark_lock
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* inode->i_lock
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*/
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spin_lock(&mark->lock);
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spin_lock(&group->mark_lock);
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mark->flags |= FSNOTIFY_MARK_FLAG_ALIVE;
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mark->group = group;
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list_add(&mark->g_list, &group->marks_list);
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atomic_inc(&group->num_marks);
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fsnotify_get_mark(mark); /* for i_list and g_list */
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if (inode) {
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ret = fsnotify_add_inode_mark(mark, group, inode, allow_dups);
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if (ret)
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goto err;
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} else if (mnt) {
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ret = fsnotify_add_vfsmount_mark(mark, group, mnt, allow_dups);
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if (ret)
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goto err;
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} else {
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BUG();
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}
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spin_unlock(&group->mark_lock);
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/* this will pin the object if appropriate */
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fsnotify_set_mark_mask_locked(mark, mark->mask);
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spin_unlock(&mark->lock);
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if (inode)
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__fsnotify_update_child_dentry_flags(inode);
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return ret;
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err:
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mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE;
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list_del_init(&mark->g_list);
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mark->group = NULL;
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atomic_dec(&group->num_marks);
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spin_unlock(&group->mark_lock);
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spin_unlock(&mark->lock);
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spin_lock(&destroy_lock);
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list_add(&mark->destroy_list, &destroy_list);
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spin_unlock(&destroy_lock);
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wake_up(&destroy_waitq);
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return ret;
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}
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/*
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* clear any marks in a group in which mark->flags & flags is true
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*/
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void fsnotify_clear_marks_by_group_flags(struct fsnotify_group *group,
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unsigned int flags)
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{
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struct fsnotify_mark *lmark, *mark;
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LIST_HEAD(free_list);
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spin_lock(&group->mark_lock);
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list_for_each_entry_safe(mark, lmark, &group->marks_list, g_list) {
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if (mark->flags & flags) {
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list_add(&mark->free_g_list, &free_list);
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list_del_init(&mark->g_list);
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fsnotify_get_mark(mark);
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}
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}
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spin_unlock(&group->mark_lock);
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list_for_each_entry_safe(mark, lmark, &free_list, free_g_list) {
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fsnotify_destroy_mark(mark);
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fsnotify_put_mark(mark);
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}
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}
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/*
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* Given a group, destroy all of the marks associated with that group.
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*/
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void fsnotify_clear_marks_by_group(struct fsnotify_group *group)
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{
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fsnotify_clear_marks_by_group_flags(group, (unsigned int)-1);
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}
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void fsnotify_duplicate_mark(struct fsnotify_mark *new, struct fsnotify_mark *old)
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{
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assert_spin_locked(&old->lock);
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new->i.inode = old->i.inode;
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new->m.mnt = old->m.mnt;
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new->group = old->group;
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new->mask = old->mask;
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new->free_mark = old->free_mark;
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}
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/*
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* Nothing fancy, just initialize lists and locks and counters.
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*/
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void fsnotify_init_mark(struct fsnotify_mark *mark,
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void (*free_mark)(struct fsnotify_mark *mark))
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{
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memset(mark, 0, sizeof(*mark));
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spin_lock_init(&mark->lock);
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atomic_set(&mark->refcnt, 1);
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mark->free_mark = free_mark;
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}
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static int fsnotify_mark_destroy(void *ignored)
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{
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struct fsnotify_mark *mark, *next;
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LIST_HEAD(private_destroy_list);
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for (;;) {
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spin_lock(&destroy_lock);
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/* exchange the list head */
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list_replace_init(&destroy_list, &private_destroy_list);
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spin_unlock(&destroy_lock);
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synchronize_srcu(&fsnotify_mark_srcu);
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list_for_each_entry_safe(mark, next, &private_destroy_list, destroy_list) {
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list_del_init(&mark->destroy_list);
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fsnotify_put_mark(mark);
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}
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wait_event_interruptible(destroy_waitq, !list_empty(&destroy_list));
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}
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return 0;
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}
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static int __init fsnotify_mark_init(void)
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{
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struct task_struct *thread;
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thread = kthread_run(fsnotify_mark_destroy, NULL,
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"fsnotify_mark");
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if (IS_ERR(thread))
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panic("unable to start fsnotify mark destruction thread.");
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return 0;
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}
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device_initcall(fsnotify_mark_init);
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