netdev - Re: [PATCH net 000/117] net: avoid to remove module when its debugfs is being used

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Date:   Fri, 9 Oct 2020 01:37:26 +0900
From:   Taehee Yoo <ap420073@...il.com>
To:     Johannes Berg <johannes@...solutions.net>
Cc:     David Laight <David.Laight@...lab.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Nicolai Stange <nicstange@...il.com>,
        "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
        "wil6210@....qualcomm.com" <wil6210@....qualcomm.com>,
        "brcm80211-dev-list@...ress.com" <brcm80211-dev-list@...ress.com>,
        "b43-dev@...ts.infradead.org" <b43-dev@...ts.infradead.org>,
        "linux-bluetooth@...r.kernel.org" <linux-bluetooth@...r.kernel.org>
Subject: Re: [PATCH net 000/117] net: avoid to remove module when its debugfs
 is being used

On Fri, 9 Oct 2020 at 01:14, Johannes Berg <johannes@...solutions.net> wrote:
On Thu, 2020-10-08 at 15:59 +0000, David Laight wrote:

Hi Johannes and David,
Thank you for the review!

> From: Taehee Yoo
> > Sent: 08 October 2020 16:49
> >
> > When debugfs file is opened, its module should not be removed until
> > it's closed.
> > Because debugfs internally uses the module's data.
> > So, it could access freed memory.
> >
> > In order to avoid panic, it just sets .owner to THIS_MODULE.
> > So that all modules will be held when its debugfs file is opened.
>
> Can't you fix it in common code?

> Yeah I was just wondering that too - weren't the proxy_fops even already
> intended to fix this?

I didn't try to fix this issue in the common code(debugfs).
Because I thought It's a typical pattern of panic and THIS_MODULE
can fix it clearly.
So I couldn't think there is a root reason in the common code.

> The modules _should_ be removing the debugfs files, and then the
> proxy_fops should kick in, no?

If I understand your mention correctly,
you mean that when the module is being removed, the opened file
should be closed automatically by debugfs filesystem.
Is that right?

> So where's the issue?

> johannes

Thanks a lot!
Taehee