linux-ext4 - Re: [PATCH v3 01/15] fsnotify: Don't insert unmergeable events in hashtable

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Date:   Wed, 30 Jun 2021 06:12:53 +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 01/15] fsnotify: Don't insert unmergeable events in hashtable

On Tue, Jun 29, 2021 at 10:11 PM Gabriel Krisman Bertazi
<krisman@...labora.com> wrote:
>
> Some events, like the overflow event, are not mergeable, so they are not
> hashed.  But, when failing inside fsnotify_add_event for lack of space,
> fsnotify_add_event() still calls the insert hook, which adds the
> overflow event to the merge list.  Add a check to prevent any kind of
> unmergeable event to be inserted in the hashtable.
>
> Fixes: 94e00d28a680 ("fsnotify: use hash table for faster events merge")
> Signed-off-by: Gabriel Krisman Bertazi <krisman@...labora.com>
>

Reviewed-by: Amir Goldstein <amir73il@...il.com>

> ---
> Changes since v2:
>   - Do check for hashed events inside the insert hook (Amir)
> ---
>  fs/notify/fanotify/fanotify.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/fs/notify/fanotify/fanotify.c b/fs/notify/fanotify/fanotify.c
> index 057abd2cf887..310246f8d3f1 100644
> --- a/fs/notify/fanotify/fanotify.c
> +++ b/fs/notify/fanotify/fanotify.c
> @@ -702,6 +702,9 @@ static void fanotify_insert_event(struct fsnotify_group *group,
>
>         assert_spin_locked(&group->notification_lock);
>
> +       if (!fanotify_is_hashed_event(event->mask))
> +               return;
> +
>         pr_debug("%s: group=%p event=%p bucket=%u\n", __func__,
>                  group, event, bucket);
>
> @@ -779,8 +782,7 @@ static int fanotify_handle_event(struct fsnotify_group *group, u32 mask,
>
>         fsn_event = &event->fse;
>         ret = fsnotify_add_event(group, fsn_event, fanotify_merge,
> -                                fanotify_is_hashed_event(mask) ?
> -                                fanotify_insert_event : NULL);
> +                                fanotify_insert_event);
>         if (ret) {
>                 /* Permission events shouldn't be merged */
>                 BUG_ON(ret == 1 && mask & FANOTIFY_PERM_EVENTS);
> --
> 2.32.0
>