linux-ext4 - [PATCH v3 09/15] fsnotify: Always run the merge hook

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Date:   Tue, 29 Jun 2021 15:10:29 -0400
From:   Gabriel Krisman Bertazi <krisman@...labora.com>
To:     amir73il@...il.com
Cc:     djwong@...nel.org, tytso@....edu, david@...morbit.com,
        jack@...e.com, dhowells@...hat.com, khazhy@...gle.com,
        linux-fsdevel@...r.kernel.org, linux-ext4@...r.kernel.org,
        Gabriel Krisman Bertazi <krisman@...labora.com>,
        kernel@...labora.com
Subject: [PATCH v3 09/15] fsnotify: Always run the merge hook

FS_FAN_ERROR must be able to merge events even in the short window after
they've been unqueued but prior to being read.  Move the list_empty
check into the merge hooks, such that merge() is always invoked if
existing.

Signed-off-by: Gabriel Krisman Bertazi <krisman@...labora.com>
---
 fs/notify/fanotify/fanotify.c        | 3 ++-
 fs/notify/inotify/inotify_fsnotify.c | 3 +++
 fs/notify/notification.c             | 2 +-
 3 files changed, 6 insertions(+), 2 deletions(-)

diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
index aba06b84da91..769703ef2b9a 100644
--- a/fs/notify/fanotify/fanotify.c
+++ b/fs/notify/fanotify/fanotify.c
@@ -168,7 +168,8 @@ static int fanotify_merge(struct fsnotify_group *group,
 	 * the event structure we have created in fanotify_handle_event() is the
 	 * one we should check for permission response.
 	 */
-	if (fanotify_is_perm_event(new->mask))
+	if (list_empty(&group->notification_list) ||
+	    fanotify_is_perm_event(new->mask))
 		return 0;
 
 	hlist_for_each_entry(old, hlist, merge_list) {
diff --git a/fs/notify/inotify/inotify_fsnotify.c b/fs/notify/inotify/inotify_fsnotify.c
index a003a64ff8ee..2f357b4933c2 100644
--- a/fs/notify/inotify/inotify_fsnotify.c
+++ b/fs/notify/inotify/inotify_fsnotify.c
@@ -52,6 +52,9 @@ static int inotify_merge(struct fsnotify_group *group,
 	struct list_head *list = &group->notification_list;
 	struct fsnotify_event *last_event;
 
+	if (list_empty(list))
+		return 0;
+
 	last_event = list_entry(list->prev, struct fsnotify_event, list);
 	return event_compare(last_event, event);
 }
diff --git a/fs/notify/notification.c b/fs/notify/notification.c
index 0d9ba592d725..1d06e0728a24 100644
--- a/fs/notify/notification.c
+++ b/fs/notify/notification.c
@@ -111,7 +111,7 @@ int fsnotify_add_event(struct fsnotify_group *group,
 		goto queue;
 	}
 
-	if (!list_empty(list) && merge) {
+	if (merge) {
 		ret = merge(group, event);
 		if (ret) {
 			spin_unlock(&group->notification_lock);
-- 
2.32.0