[PATCH v3 8/8] fsnotify: optimize away srcu_read_lock() for events on directories

[Amir Goldstein <amir73il@gmail.com>]

inotify and dnotify are always interested in events on directories.
fanotify is interested in events on directories only if user requested
them by flag FAN_ONDIR.

For the fanotify supported events on directories (open/access/close),
if there is no inotify/dnotify associated marks and if none of the
associated fanotify marks have the FS_ISDIR flag, we can skip iterating
the marks and we avoid taking the srcu_read_lock() for all events on
directories.

In order to enable this check in fsnotify() we set the FS_ISDIR flag
explicitly on all dnotify/inotify marks.

Signed-off-by: Amir Goldstein <amir73il@gmail.com>
---
 fs/notify/dnotify/dnotify.c      | 5 +++--
 fs/notify/fsnotify.c             | 9 ++++++++-
 fs/notify/inotify/inotify_user.c | 4 ++--
 3 files changed, 13 insertions(+), 5 deletions(-)

diff --git a/fs/notify/dnotify/dnotify.c b/fs/notify/dnotify/dnotify.c
index 58d77dc696eb..55f0ae5fe0ba 100644
--- a/fs/notify/dnotify/dnotify.c
+++ b/fs/notify/dnotify/dnotify.c
@@ -89,7 +89,7 @@ static int dnotify_handle_event(struct fsnotify_group *group,
 	struct dnotify_struct *dn;
 	struct dnotify_struct **prev;
 	struct fown_struct *fown;
-	__u32 test_mask = mask & ~FS_EVENT_ON_CHILD;
+	__u32 test_mask = mask & ALL_FSNOTIFY_EVENTS;
 
 	/* not a dir, dnotify doesn't care */
 	if (!S_ISDIR(inode->i_mode))
@@ -197,7 +197,8 @@ void dnotify_flush(struct file *filp, fl_owner_t id)
 /* this conversion is done only at watch creation */
 static __u32 convert_arg(unsigned long arg)
 {
-	__u32 new_mask = FS_EVENT_ON_CHILD;
+	/* Interested in events on children including subdirs */
+	__u32 new_mask = FS_EVENT_ON_CHILD | FS_ISDIR;
 
 	if (arg & DN_MULTISHOT)
 		new_mask |= FS_DN_MULTISHOT;
diff --git a/fs/notify/fsnotify.c b/fs/notify/fsnotify.c
index 875975504409..a0ad06285450 100644
--- a/fs/notify/fsnotify.c
+++ b/fs/notify/fsnotify.c
@@ -332,9 +332,16 @@ int fsnotify(struct inode *to_tell, __u32 mask, const void *data, int data_is,
 	__u32 test_mask = (mask & ALL_FSNOTIFY_EVENTS);
 
 	if (data_is == FSNOTIFY_EVENT_PATH) {
-		mnt = real_mount(((const struct path *)data)->mnt);
+		const struct path *path = data;
+
+		mnt = real_mount(path->mnt);
 		sb = mnt->mnt.mnt_sb;
 		mnt_or_sb_mask = mnt->mnt_fsnotify_mask | sb->s_fsnotify_mask;
+
+		/* Is anybody is interested in events on directories? */
+		if (d_is_dir(path->dentry) &&
+		    !(FS_ISDIR & (to_tell->i_fsnotify_mask | mnt_or_sb_mask)))
+			return 0;
 	}
 
 	/*
diff --git a/fs/notify/inotify/inotify_user.c b/fs/notify/inotify/inotify_user.c
index 105576daca4a..8d163b96a86a 100644
--- a/fs/notify/inotify/inotify_user.c
+++ b/fs/notify/inotify/inotify_user.c
@@ -91,9 +91,9 @@ static inline __u32 inotify_arg_to_mask(u32 arg)
 
 	/*
 	 * everything should accept their own ignored, cares about children,
-	 * and should receive events when the inode is unmounted
+	 * directories, and should receive events when the inode is unmounted.
 	 */
-	mask = (FS_IN_IGNORED | FS_EVENT_ON_CHILD | FS_UNMOUNT);
+	mask = (FS_IN_IGNORED | FS_EVENT_ON_CHILD | FS_ISDIR | FS_UNMOUNT);
 
 	/* mask off the flags used to open the fd */
 	mask |= (arg & (IN_ALL_EVENTS | IN_ONESHOT | IN_EXCL_UNLINK));
-- 
2.17.1