fanotify: allow freeze when waiting response for permission events

This is a long-standing issue that uninterruptible sleep in fanotify
could make system hibernation fail if the usperspace server gets frozen
before the process waiting for the response (as reported e.g. [1][2]).

A few years ago, there was an attempt to switch to interruptible sleep
while waiting [3], but that would lead to EINTR returns from open(2)
and break userspace [4], so it's been changed to only killable [5].

And the core freezer logic had been rewritten [6][7] in v6.1, allowing
freezing in uninterrupted sleep, so we can solve this problem now.

[1] https://lore.kernel.org/lkml/[email protected]/
[2] https://lore.kernel.org/lkml/[email protected]/
[3] https://lore.kernel.org/linux-fsdevel/[email protected]/
[4] https://lore.kernel.org/linux-fsdevel/[email protected]/
[5] https://lore.kernel.org/linux-fsdevel/[email protected]/
[6] https://lore.kernel.org/lkml/[email protected]/
[7] https://lore.kernel.org/lkml/20230908-avoid-spurious-freezer-wakeups-v4-0-6155aa3dafae@quicinc.com/

Signed-off-by: Winston Wen <[email protected]>
Signed-off-by: Jan Kara <[email protected]>
Message-Id: <[email protected]>

Author: winnscode

fs/notify/fanotify/fanotify.c

@@ -228,8 +228,10 @@ static int fanotify_get_response(struct fsnotify_group *group,
 
 	pr_debug("%s: group=%p event=%p\n", __func__, group, event);
 
-	ret = wait_event_killable(group->fanotify_data.access_waitq,
-				  event->state == FAN_EVENT_ANSWERED);
+	ret = wait_event_state(group->fanotify_data.access_waitq,
+				  event->state == FAN_EVENT_ANSWERED,
+				  (TASK_KILLABLE|TASK_FREEZABLE));
+
 	/* Signal pending? */
 	if (ret < 0) {
 		spin_lock(&group->notification_lock);