linux-kernel - Re: [PATCH 2/2] drivers: core: Remove glue dirs from sysfs earlier

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Message-Id: <b74e1b91b54053d85ee052b034f812769f13ee5e.camel@au1.ibm.com>
Date:   Sat, 30 Jun 2018 13:51:48 +1000
From:   Benjamin Herrenschmidt <benh@....ibm.com>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        Joel Stanley <joel@....id.au>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/2] drivers: core: Remove glue dirs from sysfs earlier

On Sat, 2018-06-30 at 11:04 +1000, Benjamin Herrenschmidt wrote:
> I had a look (see my other email). It's non-trivial. We can still look
> into it, but from what I gathered of how sysfs works, it's based on
> kernfs which doesn't have the kobjects nor access to the reference
> count, and is the holder of the names rbtree.
> 
> So we'd need to find a way to convey that "in-use" information down to
> kernfs (I thought maybe adding an optional pointer to a kref ? but
> then, it's still somewhat racy ...)
> 
> Additionally, we would need a few more pairs of eyes to make sure that
> sticking duplicates in that rbtree isn't going to break some corner
> case in there.

Just to clarify, I will look into it, but it will take more time so I'm
keen on having the low hanging fixes in now.

Also in general, I dislike the idea of leaving things in sysfs with a
refcount of 0. That "late" cleanup in kobject_release() looks to me
more like a band-aid than a feature.

I'd be almost tempted to stick a WARN_ON in there and see who gets hit
but I worry it's going send me down one of those rabbit holes and my
time is limited these days ;-)

Cheers,
Ben.