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Commit 04662cab authored by Jan Kara's avatar Jan Kara
Browse files

fsnotify: Lock object list with connector lock 



So far list of marks attached to an object (inode / vfsmount) was
protected by i_lock or mnt_root->d_lock. This dictates that the list
must be empty before the object can be destroyed although the list is
now anchored in the fsnotify_mark_connector structure. Protect the list
by a spinlock in the fsnotify_mark_connector structure to decouple
lifetime of a list of marks from a lifetime of the object. This also
simplifies the code quite a bit since we don't have to differentiate
between inode and vfsmount lists in quite a few places anymore.

Reviewed-by: default avatarMiklos Szeredi <mszeredi@redhat.com>
Reviewed-by: default avatarAmir Goldstein <amir73il@gmail.com>
Signed-off-by: default avatarJan Kara <jack@suse.cz>
parent 2629718d

fs/notify/mark.c

+32 −58
Original line number Diff line number Diff line
@@ -33,7 +33,7 @@ 
 *

 * group->mark_mutex

 * mark->lock

 * inode->i_lock

 * mark->connector->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
@@ -44,10 +44,12 @@ 
 * 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

 * free_i_list)

 * mark->connector->lock protects the list of marks anchored inside an

 * inode / vfsmount and each mark is hooked via the i_list.

 *

 * A list of notification marks relating to inode / mnt is contained in

 * fsnotify_mark_connector. That structure is alive as long as there are any

 * marks in the list and is also protected by fsnotify_mark_srcu.

 *

 * LIFETIME:

 * Inode marks survive between when they are added to an inode and when their
@@ -110,8 +112,10 @@ static void __fsnotify_recalc_mask(struct fsnotify_mark_connector *conn) 
	u32 new_mask = 0;

	struct fsnotify_mark *mark;



	assert_spin_locked(&conn->lock);

	hlist_for_each_entry(mark, &conn->list, obj_list)

		new_mask |= mark->mask;



	if (conn->flags & FSNOTIFY_OBJ_TYPE_INODE)

		conn->inode->i_fsnotify_mask = new_mask;

	else if (conn->flags & FSNOTIFY_OBJ_TYPE_VFSMOUNT)
@@ -128,31 +132,20 @@ void fsnotify_recalc_mask(struct fsnotify_mark_connector *conn) 
	if (!conn)

		return;



	if (conn->flags & FSNOTIFY_OBJ_TYPE_INODE)

		spin_lock(&conn->inode->i_lock);

	else

		spin_lock(&conn->mnt->mnt_root->d_lock);

	spin_lock(&conn->lock);

	__fsnotify_recalc_mask(conn);

	if (conn->flags & FSNOTIFY_OBJ_TYPE_INODE) {

		spin_unlock(&conn->inode->i_lock);

	spin_unlock(&conn->lock);

	if (conn->flags & FSNOTIFY_OBJ_TYPE_INODE)

		__fsnotify_update_child_dentry_flags(conn->inode);

	} else {

		spin_unlock(&conn->mnt->mnt_root->d_lock);

	}

}



static struct inode *fsnotify_detach_from_object(struct fsnotify_mark *mark)

{

	struct fsnotify_mark_connector *conn;

	struct inode *inode = NULL;

	spinlock_t *lock;



	conn = mark->connector;

	if (conn->flags & FSNOTIFY_OBJ_TYPE_INODE)

		lock = &conn->inode->i_lock;

	else

		lock = &conn->mnt->mnt_root->d_lock;

	spin_lock(lock);

	spin_lock(&conn->lock);

	hlist_del_init_rcu(&mark->obj_list);

	if (hlist_empty(&conn->list)) {

		if (conn->flags & FSNOTIFY_OBJ_TYPE_INODE)
@@ -160,7 +153,7 @@ static struct inode *fsnotify_detach_from_object(struct fsnotify_mark *mark) 
	}

	__fsnotify_recalc_mask(conn);

	mark->connector = NULL;

	spin_unlock(lock);

	spin_unlock(&conn->lock);



	return inode;

}
@@ -326,7 +319,6 @@ int fsnotify_compare_groups(struct fsnotify_group *a, struct fsnotify_group *b) 


static int fsnotify_attach_connector_to_object(

					struct fsnotify_mark_connector **connp,

					spinlock_t *lock,

					struct inode *inode,

					struct vfsmount *mnt)

{
@@ -335,6 +327,7 @@ static int fsnotify_attach_connector_to_object( 
	conn = kmem_cache_alloc(fsnotify_mark_connector_cachep, GFP_KERNEL);

	if (!conn)

		return -ENOMEM;

	spin_lock_init(&conn->lock);

	INIT_HLIST_HEAD(&conn->list);

	if (inode) {

		conn->flags = FSNOTIFY_OBJ_TYPE_INODE;
@@ -344,16 +337,13 @@ static int fsnotify_attach_connector_to_object( 
		conn->mnt = mnt;

	}

	/*

	 * Make sure 'conn' initialization is visible. Matches

	 * lockless_dereference() in fsnotify().

	 * cmpxchg() provides the barrier so that readers of *connp can see

	 * only initialized structure

	 */

	smp_wmb();

	spin_lock(lock);

	if (!*connp)

		*connp = conn;

	else

	if (cmpxchg(connp, NULL, conn)) {

		/* Someone else created list structure for us */

		kmem_cache_free(fsnotify_mark_connector_cachep, conn);

	spin_unlock(lock);

	}



	return 0;

}
@@ -371,35 +361,30 @@ static int fsnotify_add_mark_list(struct fsnotify_mark *mark, 
	struct fsnotify_mark *lmark, *last = NULL;

	struct fsnotify_mark_connector *conn;

	struct fsnotify_mark_connector **connp;

	spinlock_t *lock;

	int cmp;

	int err = 0;



	if (WARN_ON(!inode && !mnt))

		return -EINVAL;

	if (inode) {

	if (inode)

		connp = &inode->i_fsnotify_marks;

		lock = &inode->i_lock;

	} else {

	else

		connp = &real_mount(mnt)->mnt_fsnotify_marks;

		lock = &mnt->mnt_root->d_lock;

	}



	if (!*connp) {

		err = fsnotify_attach_connector_to_object(connp, lock,

							  inode, mnt);

		err = fsnotify_attach_connector_to_object(connp, inode, mnt);

		if (err)

			return err;

	}

	spin_lock(&mark->lock);

	spin_lock(lock);

	conn = *connp;

	spin_lock(&conn->lock);



	/* is mark the first mark? */

	if (hlist_empty(&conn->list)) {

		hlist_add_head_rcu(&mark->obj_list, &conn->list);

		if (inode)

			__iget(inode);

			igrab(inode);

		goto added;

	}
@@ -425,7 +410,7 @@ static int fsnotify_add_mark_list(struct fsnotify_mark *mark, 
added:

	mark->connector = conn;

out_err:

	spin_unlock(lock);

	spin_unlock(&conn->lock);

	spin_unlock(&mark->lock);

	return err;

}
@@ -449,7 +434,7 @@ int fsnotify_add_mark_locked(struct fsnotify_mark *mark, 
	 * LOCKING ORDER!!!!

	 * group->mark_mutex

	 * mark->lock

	 * inode->i_lock

	 * mark->connector->lock

	 */

	spin_lock(&mark->lock);

	mark->flags |= FSNOTIFY_MARK_FLAG_ALIVE | FSNOTIFY_MARK_FLAG_ATTACHED;
@@ -505,24 +490,19 @@ struct fsnotify_mark *fsnotify_find_mark(struct fsnotify_mark_connector *conn, 
					 struct fsnotify_group *group)

{

	struct fsnotify_mark *mark;

	spinlock_t *lock;



	if (!conn)

		return NULL;



	if (conn->flags & FSNOTIFY_OBJ_TYPE_INODE)

		lock = &conn->inode->i_lock;

	else

		lock = &conn->mnt->mnt_root->d_lock;

	spin_lock(lock);

	spin_lock(&conn->lock);

	hlist_for_each_entry(mark, &conn->list, obj_list) {

		if (mark->group == group) {

			fsnotify_get_mark(mark);

			spin_unlock(lock);

			spin_unlock(&conn->lock);

			return mark;

		}

	}

	spin_unlock(lock);

	spin_unlock(&conn->lock);

	return NULL;

}
@@ -595,16 +575,10 @@ void fsnotify_detach_group_marks(struct fsnotify_group *group) 
void fsnotify_destroy_marks(struct fsnotify_mark_connector *conn)

{

	struct fsnotify_mark *mark;

	spinlock_t *lock;



	if (!conn)

		return;



	if (conn->flags & FSNOTIFY_OBJ_TYPE_INODE)

		lock = &conn->inode->i_lock;

	else

		lock = &conn->mnt->mnt_root->d_lock;



	while (1) {

		/*

		 * We have to be careful since we can race with e.g.
@@ -613,15 +587,15 @@ void fsnotify_destroy_marks(struct fsnotify_mark_connector *conn) 
		 * we are holding mark reference so mark cannot be freed and

		 * calling fsnotify_destroy_mark() more than once is fine.

		 */

		spin_lock(lock);

		spin_lock(&conn->lock);

		if (hlist_empty(&conn->list)) {

			spin_unlock(lock);

			spin_unlock(&conn->lock);

			break;

		}

		mark = hlist_entry(conn->list.first, struct fsnotify_mark,

				   obj_list);

		fsnotify_get_mark(mark);

		spin_unlock(lock);

		spin_unlock(&conn->lock);

		fsnotify_destroy_mark(mark, mark->group);

		fsnotify_put_mark(mark);

	}

include/linux/fsnotify_backend.h

+2 −1
Original line number Diff line number Diff line
@@ -201,6 +201,7 @@ struct fsnotify_group { 
 * inode / vfsmount gets freed.

 */

struct fsnotify_mark_connector {

	spinlock_t lock;

#define FSNOTIFY_OBJ_TYPE_INODE		0x01

#define FSNOTIFY_OBJ_TYPE_VFSMOUNT	0x02

	unsigned int flags;	/* Type of object [lock] */
@@ -240,7 +241,7 @@ struct fsnotify_mark { 
	struct list_head g_list;

	/* Protects inode / mnt pointers, flags, masks */

	spinlock_t lock;

	/* List of marks for inode / vfsmount [obj_lock] */

	/* List of marks for inode / vfsmount [connector->lock] */

	struct hlist_node obj_list;

	/* Head of list of marks for an object [mark->lock, group->mark_mutex] */

	struct fsnotify_mark_connector *connector;