linux-kernel - Re: [RFC PATCH] fanotify: wake-up all waiters on release

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Message-ID: <76mwzuvqxrpml7zm3ebqaqcoimjwjda27xfyqracb7zp4cf5qv@ykpy5yabmegu>
Date: Fri, 20 Jun 2025 13:53:47 +0900
From: Sergey Senozhatsky <senozhatsky@...omium.org>
To: Jan Kara <jack@...e.cz>
Cc: Amir Goldstein <amir73il@...il.com>, 
	Matthew Bobrowski <repnop@...gle.com>, linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Sergey Senozhatsky <senozhatsky@...omium.org>
Subject: Re: [RFC PATCH] fanotify: wake-up all waiters on release

On (25/05/26 23:12), Sergey Senozhatsky wrote:
[..]
> > >  schedule+0x534/0x2540
> > >  fsnotify_destroy_group+0xa7/0x150
> > >  fanotify_release+0x147/0x160
> > >  ____fput+0xe4/0x2a0
> > >  task_work_run+0x71/0xb0
> > >  do_exit+0x1ea/0x800
> > >  do_group_exit+0x81/0x90
> > >  get_signal+0x32d/0x4e0

[..]

> @@ -945,8 +945,10 @@ static int fanotify_handle_event(struct fsnotify_group *group, u32 mask,
>         if (FAN_GROUP_FLAG(group, FANOTIFY_FID_BITS)) {
>                 fsid = fanotify_get_fsid(iter_info);
>                 /* Racing with mark destruction or creation? */
> -               if (!fsid.val[0] && !fsid.val[1])
> -                       return 0;
> +               if (!fsid.val[0] && !fsid.val[1]) {
> +                       ret = 0;
> +                       goto finish;
> +               }
>         }

Surprisingly enough, this did not help.

Jan, one more silly question:

fsnotify_get_mark_safe() and fsnotify_put_mark_wake() can be called on
NULL mark.  Is it possible that between fsnotify_prepare_user_wait(iter_info)
and fsnotify_finish_user_wait(iter_info) iter_info->marks[type] changes in
such a way that creates imbalance?  That is, fsnotify_finish_user_wait() sees
more NULL marks and hence does not rollback all the group->user_waits
increments that fsnotify_prepare_user_wait() did?