fsnotify: do not share events between notification groups

Currently fsnotify framework creates one event structure for each
notification event and links this event into all interested notification
groups.  This is done so that we save memory when several notification
groups are interested in the event.  However the need for event
structure shared between inotify & fanotify bloats the event structure
so the result is often higher memory consumption.

Another problem is that fsnotify framework keeps path references with
outstanding events so that fanotify can return open file descriptors
with its events.  This has the undesirable effect that filesystem cannot
be unmounted while there are outstanding events - a regression for
inotify compared to a situation before it was converted to fsnotify
framework.  For fanotify this problem is hard to avoid and users of
fanotify should kind of expect this behavior when they ask for file
descriptors from notified files.

This patch changes fsnotify and its users to create separate event
structure for each group.  This allows for much simpler code (~400 lines
removed by this patch) and also smaller event structures.  For example
on 64-bit system original struct fsnotify_event consumes 120 bytes, plus
additional space for file name, additional 24 bytes for second and each
subsequent group linking the event, and additional 32 bytes for each
inotify group for private data.  After the conversion inotify event
consumes 48 bytes plus space for file name which is considerably less
memory unless file names are long and there are several groups
interested in the events (both of which are uncommon).  Fanotify event
fits in 56 bytes after the conversion (fanotify doesn't care about file
names so its events don't have to have it allocated).  A win unless
there are four or more fanotify groups interested in the event.

The conversion also solves the problem with unmount when only inotify is
used as we don't have to grab path references for inotify events.

[hughd@google.com: fanotify: fix corruption preventing startup]
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Eric Paris <eparis@parisplace.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Signed-off-by: Hugh Dickins <hughd@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 49 insertions, 76 deletions

diff --git a/fs/notify/inotify/inotify_fsnotify.c b/fs/notify/inotify/inotify_fsnotify.c
index 4216308b81b4..6fabbd163d16 100644
--- a/fs/notify/inotify/inotify_fsnotify.c
+++ b/fs/notify/inotify/inotify_fsnotify.c
@@ -34,100 +34,80 @@
 #include "inotify.h"
 
 /*
- * Check if 2 events contain the same information.  We do not compare private data
- * but at this moment that isn't a problem for any know fsnotify listeners.
+ * Check if 2 events contain the same information.
  */
-static bool event_compare(struct fsnotify_event *old, struct fsnotify_event *new)
+static bool event_compare(struct fsnotify_event *old_fsn,
+			  struct fsnotify_event *new_fsn)
 {
-	if ((old->mask == new->mask) &&
-	    (old->to_tell == new->to_tell) &&
-	    (old->data_type == new->data_type) &&
-	    (old->name_len == new->name_len)) {
-		switch (old->data_type) {
-		case (FSNOTIFY_EVENT_INODE):
-			/* remember, after old was put on the wait_q we aren't
-			 * allowed to look at the inode any more, only thing
-			 * left to check was if the file_name is the same */
-			if (!old->name_len ||
-			    !strcmp(old->file_name, new->file_name))
-				return true;
-			break;
-		case (FSNOTIFY_EVENT_PATH):
-			if ((old->path.mnt == new->path.mnt) &&
-			    (old->path.dentry == new->path.dentry))
-				return true;
-			break;
-		case (FSNOTIFY_EVENT_NONE):
-			if (old->mask & FS_Q_OVERFLOW)
-				return true;
-			else if (old->mask & FS_IN_IGNORED)
-				return false;
-			return true;
-		};
-	}
+	struct inotify_event_info *old, *new;
+
+	if (old_fsn->mask & FS_IN_IGNORED)
+		return false;
+	old = INOTIFY_E(old_fsn);
+	new = INOTIFY_E(new_fsn);
+	if ((old_fsn->mask == new_fsn->mask) &&
+	    (old_fsn->inode == new_fsn->inode) &&
+	    (old->name_len == new->name_len) &&
+	    (!old->name_len || !strcmp(old->name, new->name)))
+		return true;
 	return false;
 }
 
 static struct fsnotify_event *inotify_merge(struct list_head *list,
 					    struct fsnotify_event *event)
 {
-	struct fsnotify_event_holder *last_holder;
 	struct fsnotify_event *last_event;
 
-	/* and the list better be locked by something too */
-	spin_lock(&event->lock);
-
-	last_holder = list_entry(list->prev, struct fsnotify_event_holder, event_list);
-	last_event = last_holder->event;
-	if (event_compare(last_event, event))
-		fsnotify_get_event(last_event);
-	else
-		last_event = NULL;
-
-	spin_unlock(&event->lock);
-
+	last_event = list_entry(list->prev, struct fsnotify_event, list);
+	if (!event_compare(last_event, event))
+		return NULL;
 	return last_event;
 }
 
-static int inotify_handle_event(struct fsnotify_group *group,
-				struct fsnotify_mark *inode_mark,
-				struct fsnotify_mark *vfsmount_mark,
-				struct fsnotify_event *event)
+int inotify_handle_event(struct fsnotify_group *group,
+			 struct inode *inode,
+			 struct fsnotify_mark *inode_mark,
+			 struct fsnotify_mark *vfsmount_mark,
+			 u32 mask, void *data, int data_type,
+			 const unsigned char *file_name)
 {
 	struct inotify_inode_mark *i_mark;
-	struct inode *to_tell;
-	struct inotify_event_private_data *event_priv;
-	struct fsnotify_event_private_data *fsn_event_priv;
+	struct inotify_event_info *event;
 	struct fsnotify_event *added_event;
-	int wd, ret = 0;
+	struct fsnotify_event *fsn_event;
+	int ret = 0;
+	int len = 0;
+	int alloc_len = sizeof(struct inotify_event_info);
 
 	BUG_ON(vfsmount_mark);
 
-	pr_debug("%s: group=%p event=%p to_tell=%p mask=%x\n", __func__, group,
-		 event, event->to_tell, event->mask);
+	if (file_name) {
+		len = strlen(file_name);
+		alloc_len += len + 1;
+	}
 
-	to_tell = event->to_tell;
+	pr_debug("%s: group=%p inode=%p mask=%x\n", __func__, group, inode,
+		 mask);
 
 	i_mark = container_of(inode_mark, struct inotify_inode_mark,
 			      fsn_mark);
-	wd = i_mark->wd;
 
-	event_priv = kmem_cache_alloc(event_priv_cachep, GFP_KERNEL);
-	if (unlikely(!event_priv))
+	event = kmalloc(alloc_len, GFP_KERNEL);
+	if (unlikely(!event))
 		return -ENOMEM;
 
-	fsn_event_priv = &event_priv->fsnotify_event_priv_data;
+	fsn_event = &event->fse;
+	fsnotify_init_event(fsn_event, inode, mask);
+	event->wd = i_mark->wd;
+	event->name_len = len;
+	if (len)
+		strcpy(event->name, file_name);
 
-	fsnotify_get_group(group);
-	fsn_event_priv->group = group;
-	event_priv->wd = wd;
-
-	added_event = fsnotify_add_notify_event(group, event, fsn_event_priv, inotify_merge);
+	added_event = fsnotify_add_notify_event(group, fsn_event, inotify_merge);
 	if (added_event) {
-		inotify_free_event_priv(fsn_event_priv);
-		if (!IS_ERR(added_event))
-			fsnotify_put_event(added_event);
-		else
+		/* Our event wasn't used in the end. Free it. */
+		fsnotify_destroy_event(group, fsn_event);
+		if (IS_ERR(added_event))
 			ret = PTR_ERR(added_event);
 	}
 
@@ -202,22 +182,15 @@ static void inotify_free_group_priv(struct fsnotify_group *group)
 	free_uid(group->inotify_data.user);
 }
 
-void inotify_free_event_priv(struct fsnotify_event_private_data *fsn_event_priv)
+static void inotify_free_event(struct fsnotify_event *fsn_event)
 {
-	struct inotify_event_private_data *event_priv;
-
-
-	event_priv = container_of(fsn_event_priv, struct inotify_event_private_data,
-				  fsnotify_event_priv_data);
-
-	fsnotify_put_group(fsn_event_priv->group);
-	kmem_cache_free(event_priv_cachep, event_priv);
+	kfree(INOTIFY_E(fsn_event));
 }
 
 const struct fsnotify_ops inotify_fsnotify_ops = {
 	.handle_event = inotify_handle_event,
 	.should_send_event = inotify_should_send_event,
 	.free_group_priv = inotify_free_group_priv,
-	.free_event_priv = inotify_free_event_priv,
+	.free_event = inotify_free_event,
 	.freeing_mark = inotify_freeing_mark,
 };