netdev - Re: [CRAZY-RFF] debugfs: track open files and release on remove

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Date:   Fri, 09 Oct 2020 10:06:14 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     linux-kernel@...r.kernel.org, nstange@...e.de, ap420073@...il.com,
        David.Laight@...lab.com, netdev@...r.kernel.org,
        linux-wireless@...r.kernel.org, rafael@...nel.org
Subject: Re: [CRAZY-RFF] debugfs: track open files and release on remove

On Fri, 2020-10-09 at 10:03 +0200, Greg KH wrote:

> For lots of debugfs files, .owner should already be set, if you use the
> DEFINE_SIMPLE_ATTRIBUTE() or DEFINE_DEBUGFS_ATTRIBUTE() macros.
> 
> But yes, not all.

Right.

You didn't see the original thread:

https://lore.kernel.org/netdev/20201008155048.17679-1-ap420073@gmail.com/

> I thought the proxy-ops stuff was supposed to fix this issue already.
> Why isn't it, what is broken in them that causes this to still crash?

Well exactly what I described - the proxy_fops *release* doesn't get
proxied, since we don't have any knowledge of the open files (without
this patch) when the proxy_fops are redirected to nothing when a file is
removed.

Nicolai also discussed it a bit here:

https://lore.kernel.org/netdev/87v9fkgf4i.fsf@suse.de/

> And of course, removing kernel modules is never a guaranteed operation,
> nor is it anything that ever happens automatically, so is this really an
> issue?  :)

:)

We used to say the proxy_fops weren't needed and it wasn't an issue, and
then still implemented it. Dunno. I'm not really too concerned about it
myself, only root can hold the files open and remove modules ...

johannes