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

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Date:   Fri, 09 Oct 2020 10:44:35 +0200
From:   Johannes Berg <johannes@...solutions.net>
To:     David Laight <David.Laight@...LAB.COM>,
        Greg KH <gregkh@...uxfoundation.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "nstange@...e.de" <nstange@...e.de>,
        "ap420073@...il.com" <ap420073@...il.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
        "rafael@...nel.org" <rafael@...nel.org>
Subject: Re: [CRAZY-RFF] debugfs: track open files and release on remove

On Fri, 2020-10-09 at 08:34 +0000, David Laight wrote:
> 
> > I think adding the .owner everywhere would be good, and perhaps we can
> > somehow put a check somewhere like
> > 
> > 	WARN_ON(is_module_address((unsigned long)fops) && !fops->owner);
> > 
> > to prevent the issue in the future?
> 
> Does it ever make any sense to set .owner to anything other than
> THIS_MODULE?

No. But I believe THIS_MODULE is NULL for built-in code, so we can't
just WARN_ON(!fops->owner).

> If not the code that saves the 'struct file_operations' address
> ought to be able to save the associated module.

No, it's const.

> I was also wondering if this affects normal opens?
> They should hold a reference on the module to stop it being unloaded.
> Does that rely on .owner being set?

Yes.

> For debugfs surely it is possible to determine and save THIS_MODULE
> when he nodes are registers and do a try_module_get() in the open?

I don't really see where to save it?

johannes