Re: [PATCH v2] inotify: do not coalesce rename events

[Amir Goldstein]

On Tue, Oct 27, 2026 at 9:20 PM Hungyu Lin <dennylin0707@xxxxxxxxx> wrote:
>
> inotify compares the mask, watch descriptor and name when coalescing
> adjacent unread events, but ignores their rename cookies. Distinct
> IN_MOVED_FROM events can therefore be coalesced, losing the cookie needed
> to match a later IN_MOVED_TO event.
>
> For example, watch two directories with IN_MOVE. Move an entry from the
> first directory into an unwatched directory, recreate it under the same
> name, then move it from the first directory into the second watched
> directory before reading the events. The second IN_MOVED_FROM is merged
> with the first, while the IN_MOVED_TO retains the second rename's cookie.
> Userspace can no longer pair the second rename's events.
>
> The original inotify implementation compared cookies before coalescing.
> The fsnotify conversion lost this comparison. Do not coalesce
> IN_MOVED_FROM or IN_MOVED_TO events, which carry the identity of their
> respective renames. Leave coalescing of other event types unchanged.
>
> Fixes: 63c882a05416 ("inotify: reimplement inotify using fsnotify")
> Cc: stable@xxxxxxxxxxxxxxx
> Suggested-by: Amir Goldstein <amir73il@xxxxxxxxx>
> Signed-off-by: Hungyu Lin <dennylin0707@xxxxxxxxx>
Reviewed-by: Amir Goldstein <amir73il@xxxxxxxxx>

> ---
>  fs/notify/inotify/inotify_fsnotify.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/fs/notify/inotify/inotify_fsnotify.c b/fs/notify/inotify/inotify_fsnotify.c
> index 7c326ec2e8a8..6e3af6452dcc 100644
> --- a/fs/notify/inotify/inotify_fsnotify.c
> +++ b/fs/notify/inotify/inotify_fsnotify.c
> @@ -36,7 +36,7 @@ static bool event_compare(struct fsnotify_event *old_fsn,
>
>         old = INOTIFY_E(old_fsn);
>         new = INOTIFY_E(new_fsn);
> -       if (old->mask & FS_IN_IGNORED)
> +       if (old->mask & (FS_IN_IGNORED | FS_MOVE))
>                 return false;
>         if ((old->mask == new->mask) &&
>             (old->wd == new->wd) &&
> --
> 2.43.0
>