netdev - Re: [PATCH net] ppp: fix race conditions in ppp_fill_forward

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Message-ID: <CALW65jYNMNArwzmpHhYj3fpfL0Oz2fRYsJz0JMDUnyByu-8z3w@mail.gmail.com>
Date: Tue, 12 Aug 2025 17:38:02 +0800
From: Qingfang Deng <dqfext@...il.com>
To: Eric Dumazet <edumazet@...gle.com>
Cc: Andrew Lunn <andrew+netdev@...n.ch>, "David S. Miller" <davem@...emloft.net>, 
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>, 
	Pablo Neira Ayuso <pablo@...filter.org>, Felix Fietkau <nbd@....name>, linux-ppp@...r.kernel.org, 
	netdev@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] ppp: fix race conditions in ppp_fill_forward_path

On Mon, Aug 11, 2025 at 5:35 PM Qingfang Deng <dqfext@...il.com> wrote:
>
> On Mon, Aug 11, 2025 at 5:19 PM Eric Dumazet <edumazet@...gle.com> wrote:
> >
> > On Mon, Aug 11, 2025 at 1:44 AM Qingfang Deng <dqfext@...il.com> wrote:
> > It is unclear if rcu_read_lock() is held at this point.
> >
> > list_first_or_null_rcu() does not have a builtin __list_check_rcu()
>
> ndo_fill_forward_path() is called by nf_tables chains, which is inside
> an RCU critical section.

Update: mtk_flow_get_wdma_info() in mtk_ppe_offload.c calls
dev_fill_forward_path() in process context without RCU, so
ppp_fill_forward_path() can be called from two different contexts.
Should I add rcu_read_lock() to mtk_flow_get_wdma_info() or
ppp_fill_forward_path()?