fsnotify: take groups mark_lock before mark lock

Race-free addition and removal of a mark to a groups mark list would be easier
if we could lock the mark list of group before we lock the specific mark.
This patch changes the order used to add/remove marks to/from mark lists from

1. mark->lock
2. group->mark_lock
3. inode->i_lock

to

1. group->mark_lock
2. mark->lock
3. inode->i_lock

Signed-off-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
Signed-off-by: Eric Paris <eparis@redhat.com>

1 files changed, 16 insertions, 10 deletions

diff --git a/fs/notify/mark.c b/fs/notify/mark.c
index 3c7a1699df3d..32447dc06c07 100644
--- a/fs/notify/mark.c
+++ b/fs/notify/mark.c
@@ -127,20 +127,27 @@ void fsnotify_destroy_mark(struct fsnotify_mark *mark)
         struct inode *inode = NULL;
 
         spin_lock(&mark->lock);
-
+        /* dont get the group from a mark that is not alive yet */
+        if (!(mark->flags & FSNOTIFY_MARK_FLAG_ALIVE)) {
+                spin_unlock(&mark->lock);
+                return;
+        }
         fsnotify_get_group(mark->group);
         group = mark->group;
+        spin_unlock(&mark->lock);
+
+        spin_lock(&group->mark_lock);
+        spin_lock(&mark->lock);
 
         /* something else already called this function on this mark */
         if (!(mark->flags & FSNOTIFY_MARK_FLAG_ALIVE)) {
                 spin_unlock(&mark->lock);
+                spin_unlock(&group->mark_lock);
                 goto put_group;
         }
 
         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);
@@ -151,8 +158,8 @@ void fsnotify_destroy_mark(struct fsnotify_mark *mark)
 
         list_del_init(&mark->g_list);
 
-        spin_unlock(&group->mark_lock);
         spin_unlock(&mark->lock);
+        spin_unlock(&group->mark_lock);
 
         spin_lock(&destroy_lock);
         list_add(&mark->destroy_list, &destroy_list);
@@ -225,13 +232,13 @@ int fsnotify_add_mark(struct fsnotify_mark *mark,
 
         /*
          * LOCKING ORDER!!!!
-         * mark->lock
          * group->mark_lock
+         * mark->lock
          * inode->i_lock
          */
-        spin_lock(&mark->lock);
         spin_lock(&group->mark_lock);
 
+        spin_lock(&mark->lock);
         mark->flags |= FSNOTIFY_MARK_FLAG_ALIVE;
 
         fsnotify_get_group(group);
@@ -252,13 +259,12 @@ int fsnotify_add_mark(struct fsnotify_mark *mark,
                 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);
 
+        spin_unlock(&group->mark_lock);
+
         if (inode)
                 __fsnotify_update_child_dentry_flags(inode);
 
@@ -270,8 +276,8 @@ err:
         mark->group = NULL;
         atomic_dec(&group->num_marks);
 
-        spin_unlock(&group->mark_lock);
         spin_unlock(&mark->lock);
+        spin_unlock(&group->mark_lock);
 
         spin_lock(&destroy_lock);
         list_add(&mark->destroy_list, &destroy_list);