inotify: do not set FS_EVENT_ON_CHILD in non-dir mark mask

FS_EVENT_ON_CHILD has currently no meaning for non-dir inode marks. In
the following patches we want to use that bit to mean that mark's
notification group cares about parent and name information. So stop
setting FS_EVENT_ON_CHILD for non-dir marks.

Link: https://lore.kernel.org/r/20200722125849.17418-3-amir73il@gmail.com
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>

Author: amir73il

fs/notify/inotify/inotify_user.c

@@ -75,15 +75,17 @@ struct ctl_table inotify_table[] = {
 };
 #endif /* CONFIG_SYSCTL */
 
-static inline __u32 inotify_arg_to_mask(u32 arg)
+static inline __u32 inotify_arg_to_mask(struct inode *inode, u32 arg)
 {
 	__u32 mask;
 
 	/*
-	 * everything should accept their own ignored, cares about children,
-	 * and should receive events when the inode is unmounted
+	 * Everything should accept their own ignored and should receive events
+	 * when the inode is unmounted.  All directories care about children.
 	 */
-	mask = (FS_IN_IGNORED | FS_EVENT_ON_CHILD | FS_UNMOUNT);
+	mask = (FS_IN_IGNORED | FS_UNMOUNT);
+	if (S_ISDIR(inode->i_mode))
+		mask |= FS_EVENT_ON_CHILD;
 
 	/* mask off the flags used to open the fd */
 	mask |= (arg & (IN_ALL_EVENTS | IN_ONESHOT | IN_EXCL_UNLINK));
@@ -512,7 +514,7 @@ static int inotify_update_existing_watch(struct fsnotify_group *group,
 	int create = (arg & IN_MASK_CREATE);
 	int ret;
 
-	mask = inotify_arg_to_mask(arg);
+	mask = inotify_arg_to_mask(inode, arg);
 
 	fsn_mark = fsnotify_find_mark(&inode->i_fsnotify_marks, group);
 	if (!fsn_mark)
@@ -565,7 +567,7 @@ static int inotify_new_watch(struct fsnotify_group *group,
 	struct idr *idr = &group->inotify_data.idr;
 	spinlock_t *idr_lock = &group->inotify_data.idr_lock;
 
-	mask = inotify_arg_to_mask(arg);
+	mask = inotify_arg_to_mask(inode, arg);
 
 	tmp_i_mark = kmem_cache_alloc(inotify_inode_mark_cachep, GFP_KERNEL);
 	if (unlikely(!tmp_i_mark))