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

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Date:   Tue, 30 Nov 2021 09:12:06 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Heiner Kallweit <hkallweit1@...il.com>
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 Tue, 30 Nov 2021 07:46:22 +0100 Heiner Kallweit wrote:
> 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.

No, no - I meant to leave the locking in but add ASSERT_RTNL() to catch
if rpm == true && rtnl_held() == false.