netdev - Re: [PATCH net v2] ravb: Fix races between ravb_tx_timeout

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Date: Wed, 15 Nov 2023 21:31:16 +0300
From: Sergey Shtylyov <s.shtylyov@....ru>
To: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>,
	"davem@...emloft.net" <davem@...emloft.net>, "edumazet@...gle.com"
	<edumazet@...gle.com>, "kuba@...nel.org" <kuba@...nel.org>,
	"pabeni@...hat.com" <pabeni@...hat.com>
CC: "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"linux-renesas-soc@...r.kernel.org" <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH net v2] ravb: Fix races between ravb_tx_timeout_work() and
 net related ops

On 11/15/23 5:09 AM, Yoshihiro Shimoda wrote:
[...]

>>> Fix races between ravb_tx_timeout_work() and functions of net_device_ops
>>> and ethtool_ops by using rtnl_trylock() and rtnl_unlock(). Note that
>>> since ravb_close() is under the rtnl lock and calls cancel_work_sync(),
>>> ravb_tx_timeout_work() should calls rtnl_trylock(). Otherwise, a deadlock
>>> may happen in ravb_tx_timeout_work() like below:
>>>
>>> CPU0			CPU1
>>> 			ravb_tx_timeout()
>>> 			schedule_work()
>>> ...
>>> __dev_close_many()
>>> // Under rtnl lock
>>> ravb_close()
>>> cancel_work_sync()
>>> // Waiting
>>> 			ravb_tx_timeout_work()
>>> 			rtnl_lock()
>>> 			// This is possible to cause a deadlock
>>>
>>> Fixes: c156633f1353 ("Renesas Ethernet AVB driver proper")
>>> Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@...esas.com>
>>
>> Reviewed-by: Sergey Shtylyov <s.shtylyov@....ru>

[...]

>>> diff --git a/drivers/net/ethernet/renesas/ravb_main.c b/drivers/net/ethernet/renesas/ravb_main.c
>>> index 0ef0b88b7145..300c1885e1e1 100644
>>> --- a/drivers/net/ethernet/renesas/ravb_main.c
>>> +++ b/drivers/net/ethernet/renesas/ravb_main.c
>>> @@ -1874,6 +1874,9 @@ static void ravb_tx_timeout_work(struct work_struct *work)
>>>  	struct net_device *ndev = priv->ndev;
>>>  	int error;
>>>
>>> +	if (!rtnl_trylock())
>>> +		return;
>>
>>    I wonder if we should reschedule the work here...
> 
> I think so. But, it should reschedule the work if the netif is still running because
> Use-after-free issue happens again when cancel_work_sync() is calling. Also, I also think
> we should use schedule_delayed_work() instead. So, I'll submit such a patch as v3.

   I'm not really sure about that one. Note that cancel_work_sync() should
work with the works requeueing themselves, the comments say...

> Best regards,
> Yoshihiro Shimoda

[...]

MBR, Sergey