Re: [PATCH net] net: spacemit: Hold RTNL lock in emac_resume() and emac_suspend()

From: Ali Tariq <alitariq45892@gmail.com>
To: Troy Mitchell <troy.mitchell@linux.spacemit.com>
Cc: Vadim Fedorenko <vadim.fedorenko@linux.dev>,
	netdev@vger.kernel.org, Andrew Lunn <andrew+netdev@lunn.ch>,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@kernel.org>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Yixun Lan <dlan@kernel.org>,
	Vivian Wang <wangruikang@iscas.ac.cn>,
	Chukun Pan <amadeus@jmu.edu.cn>,
	Siddharth Vadapalli <s-vadapalli@ti.com>,
	Tomas Hlavacek <tmshlvck@gmail.com>,
	Muhammad Bilal <meatuni001@gmail.com>,
	Maxime Chevallier <maxime.chevallier@bootlin.com>,
	linux-riscv@lists.infradead.org, spacemit@lists.linux.dev,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH net] net: spacemit: Hold RTNL lock in emac_resume() and emac_suspend()
Date: Fri, 6 Nov 2026 15:44:50 +0500	[thread overview]
Message-ID: <c55c5878-d9c1-4863-bc55-99d334ba2ede@gmail.com> (raw)
In-Reply-To: <DMO13SWAGZAN.NYISGLGI7Y5A@linux.spacemit.com>

On 11/6/26 2:43 PM, Troy Mitchell wrote:
> On Thu,  5 Nov 2026 17:34:37 +0500, Ali Tariq wrote:
>> @@ -2056,7 +2059,9 @@ static int emac_suspend(struct device *dev)
>>   		return 0;
>>   	}
>>   
>> +	rtnl_lock();
>>   	emac_stop(ndev);
>> +	rtnl_unlock();
>>   
>>   	clk_disable_unprepare(priv->bus_clk);
>>   	netif_device_detach(ndev);
> This can deadlock. emac_stop() -> emac_down() calls
> cancel_work_sync(&priv->tx_timeout_task) with RTNL now held, while
> emac_tx_timeout_task() starts with rtnl_lock().
> 

Thanks Troy, that makes sense.

For the deadlock, I think the correct function to call is rtnl_trylock() 
inside the emac_tx_timeout_task(), which would return if the lock is 
already held and will hold the lock if it is not.

What are your thoughts on this? Does a v2 changing rtnl_lock() to 
rtnl_trylock() inside emac_tx_timeout_task() make sense?

Regards,
Ali

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