linux-kernel - Re: [Intel-wired-lan] [iwl-next v4 2/2] igc: Link queues to NAPI instances

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Message-ID: <Zx_fD72US_Jhq1oL@LQ3V64L9R2>
Date: Mon, 28 Oct 2024 11:59:27 -0700
From: Joe Damato <jdamato@...tly.com>
To: Jacob Keller <jacob.e.keller@...el.com>
Cc: "Lifshits, Vitaly" <vitaly.lifshits@...el.com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"kurt@...utronix.de" <kurt@...utronix.de>,
	"Gomes, Vinicius" <vinicius.gomes@...el.com>,
	"Nguyen, Anthony L" <anthony.l.nguyen@...el.com>,
	"Kitszel, Przemyslaw" <przemyslaw.kitszel@...el.com>,
	Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Alexei Starovoitov <ast@...nel.org>,
	Daniel Borkmann <daniel@...earbox.net>,
	Jesper Dangaard Brouer <hawk@...nel.org>,
	John Fastabend <john.fastabend@...il.com>,
	"moderated list:INTEL ETHERNET DRIVERS" <intel-wired-lan@...ts.osuosl.org>,
	open list <linux-kernel@...r.kernel.org>,
	"open list:XDP (eXpress Data Path)" <bpf@...r.kernel.org>,
	stanislaw.gruszka@...ux.intel.com
Subject: Re: [Intel-wired-lan] [iwl-next v4 2/2] igc: Link queues to NAPI
 instances

On Mon, Oct 28, 2024 at 11:53:55AM -0700, Jacob Keller wrote:
> 
> 
> On 10/28/2024 9:00 AM, Joe Damato wrote:
> > 
> > I see, so it looks like there is:
> >    - resume
> >    - runtime_resume
> > 
> > The bug I am reintroducing is runtime_resume already holding RTNL
> > before my added call to rtnl_lock.
> > 
> > OK.
> > 
> > Does resume also hold rtnl before the driver's igc_resume is called?
> > I am asking because I don't know much about how PM works.
> > 
> > If resume does not hold RTNL (but runtime resume does, as the bug
> > you pointed out shows), it seems like a wrapper can be added to tell
> > the code whether rtnl should be held or not based on which resume is
> > happening.
> > 
> > Does anyone know if: resume (not runtime_resume) already holds RTNL?
> > I'll try to take a look and see, but I am not very familiar with PM.
> 
> I believe the resume doesn't hold RTNL, as its part of the core device
> code, which is not networking specific. It shouldn't be acquiring RTNL
> since that is a network specific lock.
> 
> I believe the code you posted as v5 should resolve this, and makes sense
> to me.
> 
> Thanks for digging into this :)

No problem; sorry for all the back and forth on this one and I
really appreciate your patience and reviews.

Thanks,
Joe