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From:   Nicolai Stange <nstange@suse.de>
To:     Taehee Yoo <ap420073@gmail.com>
Cc:     Johannes Berg <johannes@sipsolutions.net>,
        David Laight <David.Laight@aculab.com>,
        "davem\@davemloft.net" <davem@davemloft.net>,
        "kuba\@kernel.org" <kuba@kernel.org>,
        "netdev\@vger.kernel.org" <netdev@vger.kernel.org>,
        Nicolai Stange <nstange@suse.de>,
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        "wil6210\@qti.qualcomm.com" <wil6210@qti.qualcomm.com>,
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Subject: Re: [PATCH net 000/117] net: avoid to remove module when its debugfs is being used
References: <20201008155048.17679-1-ap420073@gmail.com>
        <1cbb69d83188424e99b2d2482848ae64@AcuMS.aculab.com>
        <62f6c2bd11ed8b25c1cd4462ebc6db870adc4229.camel@sipsolutions.net>
        <CAMArcTUkC2MzN9MiTu_Qwouj6rFf0g0ac2uZWfSKWHTW9cR8xA@mail.gmail.com>
Date:   Fri, 09 Oct 2020 07:38:59 +0200
In-Reply-To: <CAMArcTUkC2MzN9MiTu_Qwouj6rFf0g0ac2uZWfSKWHTW9cR8xA@mail.gmail.com>
        (Taehee Yoo's message of "Fri, 9 Oct 2020 01:37:26 +0900")
Message-ID: <87r1q8gdqk.fsf@suse.de>
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Taehee Yoo <ap420073@gmail.com> writes:

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

Yes, the file_operations' ->release() to be more specific -- that's not
covered by debugfs' proxy fops.


>> > 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.

That's correct, ->owner should get set properly, c.f. my other mail in
this thread.


Thanks,

Nicolai

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