Re: [PATCH v7 19/28] fanotify: Limit number of marks with FAN_FS_ERROR per group

From: Amir Goldstein <amir73il@gmail.com>
To: Gabriel Krisman Bertazi <krisman@collabora.com>
Cc: Jan Kara <jack@suse.com>, "Darrick J. Wong" <djwong@kernel.org>,
	Theodore Tso <tytso@mit.edu>, David Howells <dhowells@redhat.com>,
	Khazhismel Kumykov <khazhy@google.com>,
	linux-fsdevel <linux-fsdevel@vger.kernel.org>,
	Ext4 <linux-ext4@vger.kernel.org>,
	Linux API <linux-api@vger.kernel.org>,
	Matthew Bobrowski <repnop@google.com>,
	kernel@collabora.com
Subject: Re: [PATCH v7 19/28] fanotify: Limit number of marks with FAN_FS_ERROR per group
Date: Fri, 15 Oct 2021 09:15:46 +0300	[thread overview]
Message-ID: <CAOQ4uxjhTu+fPwZfjGtzcoj3-RLxBSh8ozyLjWzcTC0YJAwnwA@mail.gmail.com> (raw)
In-Reply-To: <20211014213646.1139469-20-krisman@collabora.com>

On Fri, Oct 15, 2021 at 12:39 AM Gabriel Krisman Bertazi
<krisman@collabora.com> wrote:
>
> Since FAN_FS_ERROR memory must be pre-allocated, limit a single group
> from watching too many file systems at once.  The current scheme
> guarantees 1 slot per filesystem, so limit the number of marks with
> FAN_FS_ERROR per group.
>
> Signed-off-by: Gabriel Krisman Bertazi <krisman@collabora.com>
> ---
>  fs/notify/fanotify/fanotify_user.c | 10 ++++++++++
>  include/linux/fsnotify_backend.h   |  1 +
>  2 files changed, 11 insertions(+)
>
> diff --git a/fs/notify/fanotify/fanotify_user.c b/fs/notify/fanotify/fanotify_user.c
> index f1cf863d6f9f..5324890500fc 100644
> --- a/fs/notify/fanotify/fanotify_user.c
> +++ b/fs/notify/fanotify/fanotify_user.c
> @@ -959,6 +959,10 @@ static int fanotify_remove_mark(struct fsnotify_group *group,
>
>         removed = fanotify_mark_remove_from_mask(fsn_mark, mask, flags,
>                                                  umask, &destroy_mark);
> +
> +       if (removed & FAN_FS_ERROR)
> +               group->fanotify_data.error_event_marks--;
> +
>         if (removed & fsnotify_conn_mask(fsn_mark->connector))
>                 fsnotify_recalc_mask(fsn_mark->connector);
>         if (destroy_mark)
> @@ -1057,6 +1061,9 @@ static struct fsnotify_mark *fanotify_add_new_mark(struct fsnotify_group *group,
>
>  static int fanotify_group_init_error_pool(struct fsnotify_group *group)
>  {
> +       if (group->fanotify_data.error_event_marks >= FANOTIFY_DEFAULT_FEE_POOL)
> +               return -ENOMEM;

Why not try to mempool_resize()?
Also, I did not read the rest of the patches yet, but don't we need two
slots per mark? one for alloc-pre-enqueue and one for free-post-dequeue?

Thanks,
Amir.