From 623af4f538b5df9b416e1b82f720af7371b4c771 Mon Sep 17 00:00:00 2001
From: Amir Goldstein <amir73il@gmail.com>
Date: Fri, 22 Apr 2022 15:03:14 +0300
Subject: [PATCH] fsnotify: fix wrong lockdep annotations
Git-commit: 623af4f538b5df9b416e1b82f720af7371b4c771
Patch-mainline: v5.19-rc1
References: bsc#1200815

Commit 6960b0d909cd ("fsnotify: change locking order") changed some
of the mark_mutex locks in direct reclaim path to use:
  mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);

This change is explained:
 "...It uses nested locking to avoid deadlock in case we do the final
  iput() on an inode which still holds marks and thus would take the
  mutex again when calling fsnotify_inode_delete() in destroy_inode()."

The problem is that the mutex_lock_nested() is not a nested lock at
all. In fact, it has the opposite effect of preventing lockdep from
warning about a very possible deadlock.

Due to these wrong annotations, a deadlock that was introduced with
nfsd filecache in kernel v5.4 went unnoticed in v5.4.y for over two
years until it was reported recently by Khazhismel Kumykov, only to
find out that the deadlock was already fixed in kernel v5.5.

Fix the wrong lockdep annotations.

Cc: Khazhismel Kumykov <khazhy@google.com>
Fixes: 6960b0d909cd ("fsnotify: change locking order")
Link: https://lore.kernel.org/r/20220321112310.vpr7oxro2xkz5llh@quack3.lan/
Link: https://lore.kernel.org/r/20220422120327.3459282-4-amir73il@gmail.com
Signed-off-by: Amir Goldstein <amir73il@gmail.com>
Signed-off-by: Jan Kara <jack@suse.cz>
Acked-by: Jan Kara <jack@suse.cz>

---
 fs/notify/mark.c |    6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

--- a/fs/notify/mark.c
+++ b/fs/notify/mark.c
@@ -452,7 +452,7 @@ void fsnotify_free_mark(struct fsnotify_
 void fsnotify_destroy_mark(struct fsnotify_mark *mark,
 			   struct fsnotify_group *group)
 {
-	mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
+	mutex_lock(&group->mark_mutex);
 	fsnotify_detach_mark(mark);
 	mutex_unlock(&group->mark_mutex);
 	fsnotify_free_mark(mark);
@@ -767,7 +767,7 @@ void fsnotify_clear_marks_by_group(struc
 	 * move marks to free to to_free list in one go and then free marks in
 	 * to_free list one by one.
 	 */
-	mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
+	mutex_lock(&group->mark_mutex);
 	list_for_each_entry_safe(mark, lmark, &group->marks_list, g_list) {
 		if ((1U << mark->connector->type) & type_mask)
 			list_move(&mark->g_list, &to_free);
@@ -776,7 +776,7 @@ void fsnotify_clear_marks_by_group(struc
 
 clear:
 	while (1) {
-		mutex_lock_nested(&group->mark_mutex, SINGLE_DEPTH_NESTING);
+		mutex_lock(&group->mark_mutex);
 		if (list_empty(head)) {
 			mutex_unlock(&group->mark_mutex);
 			break;