fsnotify: Detach mark from object list when last reference is dropped
Instead of removing mark from object list from fsnotify_detach_mark(),
remove the mark when last reference to the mark is dropped. This will
allow fanotify to wait for userspace response to event without having to
hold onto fsnotify_mark_srcu.
To avoid pinning inodes by elevated refcount (and thus e.g. delaying
file deletion) while someone holds mark reference, we detach connector
from the object also from fsnotify_destroy_marks() and not only after
removing last mark from the list as it was now.
Reviewed-by: Miklos Szeredi <mszeredi@redhat.com>
Reviewed-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
diff --git a/fs/notify/mark.c b/fs/notify/mark.c
index df66d70..21c7791 100644
--- a/fs/notify/mark.c
+++ b/fs/notify/mark.c
@@ -49,7 +49,13 @@
*
* 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.
+ * marks in the list and is also protected by fsnotify_mark_srcu. A mark gets
+ * detached from fsnotify_mark_connector when last reference to the mark is
+ * dropped. Thus having mark reference is enough to protect mark->connector
+ * pointer and to make sure fsnotify_mark_connector cannot disappear. Also
+ * because we remove mark from g_list before dropping mark reference associated
+ * with that, any mark found through g_list is guaranteed to have
+ * mark->connector set until we drop group->mark_mutex.
*
* LIFETIME:
* Inode marks survive between when they are added to an inode and when their
@@ -103,26 +109,16 @@
atomic_inc(&mark->refcnt);
}
-void fsnotify_put_mark(struct fsnotify_mark *mark)
-{
- if (atomic_dec_and_test(&mark->refcnt)) {
- spin_lock(&destroy_lock);
- list_add(&mark->g_list, &destroy_list);
- spin_unlock(&destroy_lock);
- queue_delayed_work(system_unbound_wq, &reaper_work,
- FSNOTIFY_REAPER_DELAY);
- }
-}
-
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;
-
+ hlist_for_each_entry(mark, &conn->list, obj_list) {
+ if (mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)
+ 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)
@@ -131,8 +127,9 @@
/*
* Calculate mask of events for a list of marks. The caller must make sure
- * connector cannot disappear under us (usually by holding a mark->lock or
- * mark->group->mark_mutex for a mark on this list).
+ * connector and connector->inode cannot disappear under us. Callers achieve
+ * this by holding a mark->lock or mark->group->mark_mutex for a mark on this
+ * list.
*/
void fsnotify_recalc_mask(struct fsnotify_mark_connector *conn)
{
@@ -164,7 +161,6 @@
}
}
-
static struct inode *fsnotify_detach_connector_from_object(
struct fsnotify_mark_connector *conn)
{
@@ -187,14 +183,34 @@
return inode;
}
-static struct inode *fsnotify_detach_from_object(struct fsnotify_mark *mark)
+static void fsnotify_final_mark_destroy(struct fsnotify_mark *mark)
+{
+ if (mark->group)
+ fsnotify_put_group(mark->group);
+ mark->free_mark(mark);
+}
+
+void fsnotify_put_mark(struct fsnotify_mark *mark)
{
struct fsnotify_mark_connector *conn;
struct inode *inode = NULL;
bool free_conn = false;
+ /* Catch marks that were actually never attached to object */
+ if (!mark->connector) {
+ if (atomic_dec_and_test(&mark->refcnt))
+ fsnotify_final_mark_destroy(mark);
+ return;
+ }
+
+ /*
+ * We have to be careful so that traversals of obj_list under lock can
+ * safely grab mark reference.
+ */
+ if (!atomic_dec_and_lock(&mark->refcnt, &mark->connector->lock))
+ return;
+
conn = mark->connector;
- spin_lock(&conn->lock);
hlist_del_init_rcu(&mark->obj_list);
if (hlist_empty(&conn->list)) {
inode = fsnotify_detach_connector_from_object(conn);
@@ -205,6 +221,8 @@
mark->connector = NULL;
spin_unlock(&conn->lock);
+ iput(inode);
+
if (free_conn) {
spin_lock(&destroy_lock);
conn->destroy_next = connector_destroy_list;
@@ -212,20 +230,31 @@
spin_unlock(&destroy_lock);
queue_work(system_unbound_wq, &connector_reaper_work);
}
-
- return inode;
+ /*
+ * Note that we didn't update flags telling whether inode cares about
+ * what's happening with children. We update these flags from
+ * __fsnotify_parent() lazily when next event happens on one of our
+ * children.
+ */
+ spin_lock(&destroy_lock);
+ list_add(&mark->g_list, &destroy_list);
+ spin_unlock(&destroy_lock);
+ queue_delayed_work(system_unbound_wq, &reaper_work,
+ FSNOTIFY_REAPER_DELAY);
}
/*
- * Remove mark from inode / vfsmount list, group list, drop inode reference
- * if we got one.
+ * Mark mark as detached, remove it from group list. Mark still stays in object
+ * list until its last reference is dropped. Note that we rely on mark being
+ * removed from group list before corresponding reference to it is dropped. In
+ * particular we rely on mark->connector being valid while we hold
+ * group->mark_mutex if we found the mark through g_list.
*
* Must be called with group->mark_mutex held. The caller must either hold
* reference to the mark or be protected by fsnotify_mark_srcu.
*/
void fsnotify_detach_mark(struct fsnotify_mark *mark)
{
- struct inode *inode = NULL;
struct fsnotify_group *group = mark->group;
WARN_ON_ONCE(!mutex_is_locked(&group->mark_mutex));
@@ -234,31 +263,15 @@
!!(mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED));
spin_lock(&mark->lock);
-
/* something else already called this function on this mark */
if (!(mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) {
spin_unlock(&mark->lock);
return;
}
-
mark->flags &= ~FSNOTIFY_MARK_FLAG_ATTACHED;
-
- inode = fsnotify_detach_from_object(mark);
-
- /*
- * Note that we didn't update flags telling whether inode cares about
- * what's happening with children. We update these flags from
- * __fsnotify_parent() lazily when next event happens on one of our
- * children.
- */
-
list_del_init(&mark->g_list);
-
spin_unlock(&mark->lock);
- if (inode)
- iput(inode);
-
atomic_dec(&group->num_marks);
/* Drop mark reference acquired in fsnotify_add_mark_locked() */
@@ -458,7 +471,9 @@
hlist_for_each_entry(lmark, &conn->list, obj_list) {
last = lmark;
- if ((lmark->group == mark->group) && !allow_dups) {
+ if ((lmark->group == mark->group) &&
+ (lmark->flags & FSNOTIFY_MARK_FLAG_ATTACHED) &&
+ !allow_dups) {
err = -EEXIST;
goto out_err;
}
@@ -509,7 +524,7 @@
mark->group = group;
list_add(&mark->g_list, &group->marks_list);
atomic_inc(&group->num_marks);
- fsnotify_get_mark(mark); /* for i_list and g_list */
+ fsnotify_get_mark(mark); /* for g_list */
spin_unlock(&mark->lock);
ret = fsnotify_add_mark_list(mark, inode, mnt, allow_dups);
@@ -557,7 +572,8 @@
return NULL;
hlist_for_each_entry(mark, &conn->list, obj_list) {
- if (mark->group == group) {
+ if (mark->group == group &&
+ (mark->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) {
fsnotify_get_mark(mark);
spin_unlock(&conn->lock);
return mark;
@@ -637,23 +653,38 @@
void fsnotify_destroy_marks(struct fsnotify_mark_connector __rcu **connp)
{
struct fsnotify_mark_connector *conn;
- struct fsnotify_mark *mark;
+ struct fsnotify_mark *mark, *old_mark = NULL;
+ struct inode *inode;
- while ((conn = fsnotify_grab_connector(connp))) {
- /*
- * We have to be careful since we can race with e.g.
- * fsnotify_clear_marks_by_group() and once we drop the list
- * lock, mark can get removed from the obj_list and destroyed.
- * But we are holding mark reference so mark cannot be freed
- * and calling fsnotify_destroy_mark() more than once is fine.
- */
- mark = hlist_entry(conn->list.first, struct fsnotify_mark,
- obj_list);
+ conn = fsnotify_grab_connector(connp);
+ if (!conn)
+ return;
+ /*
+ * We have to be careful since we can race with e.g.
+ * fsnotify_clear_marks_by_group() and once we drop the conn->lock, the
+ * list can get modified. However we are holding mark reference and
+ * thus our mark cannot be removed from obj_list so we can continue
+ * iteration after regaining conn->lock.
+ */
+ hlist_for_each_entry(mark, &conn->list, obj_list) {
fsnotify_get_mark(mark);
spin_unlock(&conn->lock);
+ if (old_mark)
+ fsnotify_put_mark(old_mark);
+ old_mark = mark;
fsnotify_destroy_mark(mark, mark->group);
- fsnotify_put_mark(mark);
+ spin_lock(&conn->lock);
}
+ /*
+ * Detach list from object now so that we don't pin inode until all
+ * mark references get dropped. It would lead to strange results such
+ * as delaying inode deletion or blocking unmount.
+ */
+ inode = fsnotify_detach_connector_from_object(conn);
+ spin_unlock(&conn->lock);
+ if (old_mark)
+ fsnotify_put_mark(old_mark);
+ iput(inode);
}
/*
@@ -686,9 +717,7 @@
list_for_each_entry_safe(mark, next, &private_destroy_list, g_list) {
list_del_init(&mark->g_list);
- if (mark->group)
- fsnotify_put_group(mark->group);
- mark->free_mark(mark);
+ fsnotify_final_mark_destroy(mark);
}
}
diff --git a/include/linux/fsnotify_backend.h b/include/linux/fsnotify_backend.h
index 84d71b6..a483614 100644
--- a/include/linux/fsnotify_backend.h
+++ b/include/linux/fsnotify_backend.h
@@ -245,9 +245,9 @@
struct list_head g_list;
/* Protects inode / mnt pointers, flags, masks */
spinlock_t lock;
- /* List of marks for inode / vfsmount [connector->lock] */
+ /* List of marks for inode / vfsmount [connector->lock, mark ref] */
struct hlist_node obj_list;
- /* Head of list of marks for an object [mark->lock, group->mark_mutex] */
+ /* Head of list of marks for an object [mark ref] */
struct fsnotify_mark_connector *connector;
/* Events types to ignore [mark->lock, group->mark_mutex] */
__u32 ignored_mask;
diff --git a/kernel/audit_tree.c b/kernel/audit_tree.c
index c3b5fcb..2fa8d61 100644
--- a/kernel/audit_tree.c
+++ b/kernel/audit_tree.c
@@ -172,25 +172,16 @@
/*
* Function to return search key in our hash from chunk. Key 0 is special and
* should never be present in the hash.
- *
- * Must be called with chunk->mark.lock held to protect from connector
- * becoming NULL.
*/
-static unsigned long __chunk_to_key(struct audit_chunk *chunk)
-{
- if (!chunk->mark.connector)
- return 0;
- return (unsigned long)chunk->mark.connector->inode;
-}
-
static unsigned long chunk_to_key(struct audit_chunk *chunk)
{
- unsigned long key;
-
- spin_lock(&chunk->mark.lock);
- key = __chunk_to_key(chunk);
- spin_unlock(&chunk->mark.lock);
- return key;
+ /*
+ * We have a reference to the mark so it should be attached to a
+ * connector.
+ */
+ if (WARN_ON_ONCE(!chunk->mark.connector))
+ return 0;
+ return (unsigned long)chunk->mark.connector->inode;
}
static inline struct list_head *chunk_hash(unsigned long key)
@@ -202,7 +193,7 @@
/* hash_lock & entry->lock is held by caller */
static void insert_hash(struct audit_chunk *chunk)
{
- unsigned long key = __chunk_to_key(chunk);
+ unsigned long key = chunk_to_key(chunk);
struct list_head *list;
if (!(chunk->mark.flags & FSNOTIFY_MARK_FLAG_ATTACHED))
@@ -263,6 +254,10 @@
mutex_lock(&entry->group->mark_mutex);
spin_lock(&entry->lock);
+ /*
+ * mark_mutex protects mark from getting detached and thus also from
+ * mark->connector->inode getting NULL.
+ */
if (chunk->dead || !(entry->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) {
spin_unlock(&entry->lock);
mutex_unlock(&entry->group->mark_mutex);
@@ -423,6 +418,10 @@
mutex_lock(&old_entry->group->mark_mutex);
spin_lock(&old_entry->lock);
+ /*
+ * mark_mutex protects mark from getting detached and thus also from
+ * mark->connector->inode getting NULL.
+ */
if (!(old_entry->flags & FSNOTIFY_MARK_FLAG_ATTACHED)) {
/* old_entry is being shot, lets just lie */
spin_unlock(&old_entry->lock);