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

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Date:   Wed, 30 Jun 2021 06:42:31 +0300
From:   Amir Goldstein <amir73il@...il.com>
To:     Gabriel Krisman Bertazi <krisman@...labora.com>
Cc:     "Darrick J. Wong" <djwong@...nel.org>,
        Theodore Tso <tytso@....edu>,
        Dave Chinner <david@...morbit.com>, Jan Kara <jack@...e.com>,
        David Howells <dhowells@...hat.com>,
        Khazhismel Kumykov <khazhy@...gle.com>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        Ext4 <linux-ext4@...r.kernel.org>, kernel@...labora.com
Subject: Re: [PATCH v3 09/15] fsnotify: Always run the merge hook

On Tue, Jun 29, 2021 at 10:12 PM Gabriel Krisman Bertazi
<krisman@...labora.com> wrote:
>
> 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

This smells like trouble.
Breaking abstractions like this should be done for a very good reason
and I am not sure this is the case at hand.
More on this on merge_error_event patch.

Thanks,
Amir.

> 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
>