linux-kernel - Re: [PATCH net-next] net: ppp: remove ppp->closing check

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Message-ID: <54bbccb2-6633-4638-9dce-14683b4e320b@redhat.com>
Date: Fri, 8 Nov 2024 09:48:28 +0100
From: Paolo Abeni <pabeni@...hat.com>
To: Qingfang Deng <dqfext@...il.com>
Cc: Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller"
 <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, linux-ppp@...r.kernel.org,
 netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net-next] net: ppp: remove ppp->closing check

On 11/8/24 07:09, Qingfang Deng wrote:
> On Thu, Nov 7, 2024 at 8:08 PM Paolo Abeni <pabeni@...hat.com> wrote:
>> On 11/4/24 10:24, Qingfang Deng wrote:
>>> ppp->closing was used to test if an interface is closing down. But upon
>>> .ndo_uninit() where ppp->closing is set to 1, dev_close() is already
>>> called to bring down an interface and a synchronize_net() guarantees
>>> that no pending TX/RX can take place, so the check is unnecessary.
>>> Remove the check.
>>
>> I'm unsure we can remote such check. The TX callback can be triggered
>> even from a write on the controlling file, and it looks like such file
>> will be untouched by uninit.
> 
> ppp_release (when the file is closed) calls unregister_netdevice, and
> no more writes can happen after that.

AFAICS the device can be deleted even without closing the file, via
netlink or deleting the namespace. In such cases, AFAICS, the file is
still alive.

In any case we need a more solid explanation describing why the change
is safe (and possibly a test-case deleting the device in different ways).

/P