netdev - Re: [PATCH net] igb: fix deadlock caused by taking RTNL in RPM resume path

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Message-ID: <6edc23a1-5907-3a41-7b46-8d53c5664a56@gmail.com>
Date:   Tue, 30 Nov 2021 07:46:22 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     David Miller <davem@...emloft.net>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        Tony Nguyen <anthony.l.nguyen@...el.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        intel-wired-lan <intel-wired-lan@...ts.osuosl.org>
Subject: Re: [PATCH net] igb: fix deadlock caused by taking RTNL in RPM resume
 path

On 30.11.2021 02:17, Jakub Kicinski wrote:
> On Mon, 29 Nov 2021 22:14:06 +0100 Heiner Kallweit wrote:
>> -	rtnl_lock();
>> +	if (!rpm)
>> +		rtnl_lock();
> 
> Is there an ASSERT_RTNL() hidden in any of the below? Can we add one?
> Unless we're 100% confident nobody will RPM resume without rtnl held..
> 

Not sure whether igb uses RPM the same way as r8169. There the device
is runtime-suspended (D3hot) w/o link. Once cable is plugged in the PHY
triggers a PME, and PCI core runtime-resumes the device (MAC).
In this case RTNL isn't held by the caller. Therefore I don't think
it's safe to assume that all callers hold RTNL.

>>  	if (!err && netif_running(netdev))
>>  		err = __igb_open(netdev, true);
>>  
>>  	if (!err)
>>  		netif_device_attach(netdev);
>> -	rtnl_unlock();
>> +	if (!rpm)
>> +		rtnl_unlock();