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

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Message-ID: <CAKdAkRShA2sAMH12H_zpCm=9XJn_yEcnAaaZhLgvhaUMxC-EMw@mail.gmail.com>
Date:   Mon, 25 May 2020 15:49:01 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     lkml <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 8:34 AM 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,

^^^^ And this is the root of the problem and what has to be fixed.

> 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.

One can try, but if we keep proper reference counting then kobject
core should take care of actually releasing objects in the right
order. I do not think you should keep this patch, and instead see if
we can push call to kobject_put(kobj->parent) into kobject_cleanup().

Thanks.

-- 
Dmitry