linux-kernel - Re: [PATCH 2/2] kobject: send KOBJ_REMOVE uevent when the object is removed from sysfs

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Date:   Mon, 25 May 2020 13:07:56 +0200
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Guenter Roeck <linux@...ck-us.net>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: Re: [PATCH 2/2] kobject: send KOBJ_REMOVE uevent when the object is
 removed from sysfs

On Sun, May 24, 2020 at 5:31 PM Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
>
> It is possible for a KOBJ_REMOVE uevent to be sent to userspace way
> after the files are actually gone from sysfs, due to how reference
> counting for kobjects work.  This should not be a problem, but it would
> be good to properly send the information when things are going away, not
> at some later point in time in the future.
>
> Before this move, if a kobject's parent was torn down before the child,
> when the call to kobject_uevent() happened, the parent walk to try to
> reconstruct the full path of the kobject could be a total mess and cause
> crashes.  It's not good to try to tear down a kobject tree from top
> down, but let's at least try to not to crash if a user does so.
>
> Cc: "Rafael J. Wysocki" <rafael@...nel.org>
> Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>

LGTM

Reviewed-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

> ---
>  lib/kobject.c | 14 +++++++-------
>  1 file changed, 7 insertions(+), 7 deletions(-)
>
> diff --git a/lib/kobject.c b/lib/kobject.c
> index 83198cb37d8d..2509e22ad74a 100644
> --- a/lib/kobject.c
> +++ b/lib/kobject.c
> @@ -620,6 +620,13 @@ void kobject_del(struct kobject *kobj)
>         if (ktype)
>                 sysfs_remove_groups(kobj, ktype->default_groups);
>
> +       /* send "remove" if the caller did not do it but sent "add" */
> +       if (kobj->state_add_uevent_sent && !kobj->state_remove_uevent_sent) {
> +               pr_debug("kobject: '%s' (%p): auto cleanup 'remove' event\n",
> +                        kobject_name(kobj), kobj);
> +               kobject_uevent(kobj, KOBJ_REMOVE);
> +       }
> +
>         sysfs_remove_dir(kobj);
>         sysfs_put(sd);
>
> @@ -673,13 +680,6 @@ static void kobject_cleanup(struct kobject *kobj)
>                 pr_debug("kobject: '%s' (%p): does not have a release() function, it is broken and must be fixed. See Documentation/kobject.txt.\n",
>                          kobject_name(kobj), kobj);
>
> -       /* send "remove" if the caller did not do it but sent "add" */
> -       if (kobj->state_add_uevent_sent && !kobj->state_remove_uevent_sent) {
> -               pr_debug("kobject: '%s' (%p): auto cleanup 'remove' event\n",
> -                        kobject_name(kobj), kobj);
> -               kobject_uevent(kobj, KOBJ_REMOVE);
> -       }
> -
>         /* remove from sysfs if the caller did not do it */
>         if (kobj->state_in_sysfs) {
>                 pr_debug("kobject: '%s' (%p): auto cleanup kobject_del\n",
> --
> 2.26.2
>