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Date:   Mon, 28 Dec 2020 15:11:02 -0800 (PST)
Message-Id: <20201228.151102.1580596487777420764.davem@davemloft.net>
To:     xie.he.0141@gmail.com
Cc:     kuba@kernel.org, netdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, khc@pm.waw.pl
Subject: Re: [PATCH net v2] net: hdlc_ppp: Fix issues when mod_timer is
 called while timer is running
From:   David Miller <davem@davemloft.net>
In-Reply-To: <20201228025339.3210-1-xie.he.0141@gmail.com>
References: <20201228025339.3210-1-xie.he.0141@gmail.com>
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From: Xie He <xie.he.0141@gmail.com>
Date: Sun, 27 Dec 2020 18:53:39 -0800

> ppp_cp_event is called directly or indirectly by ppp_rx with "ppp->lock"
> held. It may call mod_timer to add a new timer. However, at the same time
> ppp_timer may be already running and waiting for "ppp->lock". In this
> case, there's no need for ppp_timer to continue running and it can just
> exit.
> 
> If we let ppp_timer continue running, it may call add_timer. This causes
> kernel panic because add_timer can't be called with a timer pending.
> This patch fixes this problem.
> 
> Fixes: e022c2f07ae5 ("WAN: new synchronous PPP implementation for generic HDLC.")
> Cc: Krzysztof Halasa <khc@pm.waw.pl>
> Signed-off-by: Xie He <xie.he.0141@gmail.com>

Applied and queued up for -stable, thanks!