* 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 guaranteed to survive until the reference is dropped.
+ * The group->recnt and mark->refcnt tell how many "things" in the kernel
+ * currently are referencing the objects. Both kind of objects typically will
+ * live inside the kernel with a refcnt of 2, one for its creation and one for
+ * the reference a group and a mark hold to each other.
+ * If you are holding the appropriate locks, you can take a reference and the
+ * object itself is guaranteed 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:
+ * There are 3 locks involved with fsnotify inode marks and they MUST be taken
+ * in order as follows:
*
+ * group->mark_mutex
* 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.
+ * group->mark_mutex protects the marks_list anchored inside a given group and
+ * each mark is hooked via the g_list. It also protects the groups private
+ * data (i.e group limits).
+
+ * mark->lock protects the marks attributes like its masks and flags.
+ * Furthermore it protects the access to a reference of the group that the mark
+ * is assigned to as well as the access to a reference of the inode/vfsmount
+ * that is being watched by the mark.
*
* 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
* 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.
- *
+ * private list anchored on the stack using i_free_list; we walk i_free_list
+ * and before we destroy the mark we make sure that we dont race with a
+ * concurrent destroy_group by getting a ref to the marks group and taking the
+ * groups mutex.
+
* 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
void fsnotify_put_mark(struct fsnotify_mark *mark)
{
- if (atomic_dec_and_test(&mark->refcnt))
+ if (atomic_dec_and_test(&mark->refcnt)) {
+ if (mark->group)
+ fsnotify_put_group(mark->group);
mark->free_mark(mark);
+ }
}
/*
* 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)
+void fsnotify_destroy_mark_locked(struct fsnotify_mark *mark,
+ struct fsnotify_group *group)
{
- struct fsnotify_group *group;
struct inode *inode = NULL;
- spin_lock(&mark->lock);
+ BUG_ON(!mutex_is_locked(&group->mark_mutex));
- group = mark->group;
+ spin_lock(&mark->lock);
/* something else already called this function on this mark */
if (!(mark->flags & FSNOTIFY_MARK_FLAG_ALIVE)) {
mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE;
- spin_lock(&group->mark_lock);
-
if (mark->flags & FSNOTIFY_MARK_FLAG_INODE) {
inode = mark->i.inode;
fsnotify_destroy_inode_mark(mark);
list_del_init(&mark->g_list);
- spin_unlock(&group->mark_lock);
spin_unlock(&mark->lock);
+ if (inode && (mark->flags & FSNOTIFY_MARK_FLAG_OBJECT_PINNED))
+ iput(inode);
+ /* release lock temporarily */
+ mutex_unlock(&group->mark_mutex);
+
spin_lock(&destroy_lock);
list_add(&mark->destroy_list, &destroy_list);
spin_unlock(&destroy_lock);
wake_up(&destroy_waitq);
+ /*
+ * We don't necessarily have a ref on mark from caller so the above destroy
+ * may have actually freed it, unless this group provides a 'freeing_mark'
+ * function which must be holding a reference.
+ */
/*
* Some groups like to know that marks are being freed. This is a
* is just a lazy update (and could be a perf win...)
*/
- if (inode && (mark->flags & FSNOTIFY_MARK_FLAG_OBJECT_PINNED))
- iput(inode);
+ atomic_dec(&group->num_marks);
- /*
- * We don't necessarily have a ref on mark from caller so the above iput
- * may have already destroyed it. Don't touch from now on.
- */
+ mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
+}
- /*
- * 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);
+void fsnotify_destroy_mark(struct fsnotify_mark *mark,
+ struct fsnotify_group *group)
+{
+ mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
+ fsnotify_destroy_mark_locked(mark, group);
+ mutex_unlock(&group->mark_mutex);
}
void fsnotify_set_mark_mask_locked(struct fsnotify_mark *mark, __u32 mask)
* 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 fsnotify_add_mark_locked(struct fsnotify_mark *mark,
+ struct fsnotify_group *group, struct inode *inode,
+ struct vfsmount *mnt, int allow_dups)
{
int ret = 0;
BUG_ON(inode && mnt);
BUG_ON(!inode && !mnt);
+ BUG_ON(!mutex_is_locked(&group->mark_mutex));
/*
* LOCKING ORDER!!!!
+ * group->mark_mutex
* mark->lock
- * group->mark_lock
* inode->i_lock
*/
spin_lock(&mark->lock);
- spin_lock(&group->mark_lock);
-
mark->flags |= FSNOTIFY_MARK_FLAG_ALIVE;
+ fsnotify_get_group(group);
mark->group = group;
list_add(&mark->g_list, &group->marks_list);
atomic_inc(&group->num_marks);
BUG();
}
- spin_unlock(&group->mark_lock);
-
/* this will pin the object if appropriate */
fsnotify_set_mark_mask_locked(mark, mark->mask);
-
spin_unlock(&mark->lock);
if (inode)
err:
mark->flags &= ~FSNOTIFY_MARK_FLAG_ALIVE;
list_del_init(&mark->g_list);
+ fsnotify_put_group(group);
mark->group = NULL;
atomic_dec(&group->num_marks);
- spin_unlock(&group->mark_lock);
spin_unlock(&mark->lock);
spin_lock(&destroy_lock);
return ret;
}
+int fsnotify_add_mark(struct fsnotify_mark *mark, struct fsnotify_group *group,
+ struct inode *inode, struct vfsmount *mnt, int allow_dups)
+{
+ int ret;
+ mutex_lock(&group->mark_mutex);
+ ret = fsnotify_add_mark_locked(mark, group, inode, mnt, allow_dups);
+ mutex_unlock(&group->mark_mutex);
+ return ret;
+}
+
/*
* clear any marks in a group in which mark->flags & flags is true
*/
unsigned int flags)
{
struct fsnotify_mark *lmark, *mark;
- LIST_HEAD(free_list);
- spin_lock(&group->mark_lock);
+ mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
list_for_each_entry_safe(mark, lmark, &group->marks_list, g_list) {
if (mark->flags & flags) {
- list_add(&mark->free_g_list, &free_list);
- list_del_init(&mark->g_list);
fsnotify_get_mark(mark);
+ fsnotify_destroy_mark_locked(mark, group);
+ fsnotify_put_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);
- }
+ mutex_unlock(&group->mark_mutex);
}
/*
assert_spin_locked(&old->lock);
new->i.inode = old->i.inode;
new->m.mnt = old->m.mnt;
+ if (old->group)
+ fsnotify_get_group(old->group);
new->group = old->group;
new->mask = old->mask;
new->free_mark = old->free_mark;
projects / ~andy / linux / blobdiff