fanotify coredump issue

["Василий Новиков" <vasiliy.novikov@gmail.com>]

[-- Attachment #1: Type: text/plain, Size: 651 bytes --]

Hi Eric,

I tested fanotify in 2.6.37-rc7 and faced the following issue: when a
fanotify server process (started with open_perm set) segfaults the
kernel tries to open core dump file and here it is forced to wait a
permission result because fanotify server receives notifications on
file operations initiated by itself. Since fanotify server has crashed
the permission will never be granted. So the whole system hangs.

I don't see the point in receiving notifications on file operations
initiated by fanotify server process so I created a patch that
disables that and solves the issue at least in case of one fanotify
server.

Best regards,
  Vasily

[-- Attachment #2: fanotify_core.patch --]
[-- Type: text/x-patch, Size: 1902 bytes --]

/usr/src/linux
--- ./fs/notify/fanotify/fanotify.c.orig	2010-12-24 12:50:33.653029001 -0500
+++ ./fs/notify/fanotify/fanotify.c	2010-12-24 13:28:19.561029005 -0500
@@ -92,6 +92,9 @@ static int fanotify_get_response_from_ac
 
 	pr_debug("%s: group=%p event=%p\n", __func__, group, event);
 
+	if(group->fanotify_data.tgid == task_tgid(current))
+		return 0;
+
 	wait_event(group->fanotify_data.access_waitq, event->response ||
 				atomic_read(&group->fanotify_data.bypass_perm));
 
@@ -217,6 +220,7 @@ static void fanotify_free_group_priv(str
 	user = group->fanotify_data.user;
 	atomic_dec(&user->fanotify_listeners);
 	free_uid(user);
+	put_pid(group->fanotify_data.tgid);
 }
 
 const struct fsnotify_ops fanotify_fsnotify_ops = {
--- ./fs/notify/fanotify/fanotify_user.c.orig	2010-12-24 12:12:07.593029001 -0500
+++ ./fs/notify/fanotify/fanotify_user.c	2010-12-27 09:26:15.259956001 -0500
@@ -337,6 +337,10 @@ static ssize_t fanotify_read(struct file
 			ret = PTR_ERR(kevent);
 			if (IS_ERR(kevent))
 				break;
+			if(kevent->tgid == group->fanotify_data.tgid) {
+				fsnotify_put_event(kevent);
+				continue;
+			}
 			ret = copy_event_to_user(group, kevent, buf);
 			fsnotify_put_event(kevent);
 			if (ret < 0)
@@ -718,6 +722,7 @@ SYSCALL_DEFINE2(fanotify_init, unsigned
 	INIT_LIST_HEAD(&group->fanotify_data.access_list);
 	atomic_set(&group->fanotify_data.bypass_perm, 0);
 #endif
+	group->fanotify_data.tgid = get_pid(task_tgid(current));
 	switch (flags & FAN_ALL_CLASS_BITS) {
 	case FAN_CLASS_NOTIF:
 		group->priority = FS_PRIO_0;
--- ./include/linux/fsnotify_backend.h.orig	2010-12-24 12:08:59.965029002 -0500
+++ ./include/linux/fsnotify_backend.h	2010-12-27 13:05:34.738636001 -0500
@@ -171,6 +171,7 @@ struct fsnotify_group {
 			int f_flags;
 			unsigned int max_marks;
 			struct user_struct *user;
+			struct pid *tgid;
 		} fanotify_data;
 #endif /* CONFIG_FANOTIFY */
 	};