linux-kernel - Re: [net-next v3 2/2] igc: Link queues to NAPI instances

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Message-ID: <40242f59-139a-4b45-8949-1210039f881b@intel.com>
Date: Tue, 22 Oct 2024 13:53:01 -0700
From: Jacob Keller <jacob.e.keller@...el.com>
To: Joe Damato <jdamato@...tly.com>, <netdev@...r.kernel.org>,
	<kurt@...utronix.de>, <vinicius.gomes@...el.com>, Tony Nguyen
	<anthony.l.nguyen@...el.com>, Przemek Kitszel <przemyslaw.kitszel@...el.com>,
	"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>
Subject: Re: [net-next v3 2/2] igc: Link queues to NAPI instances



On 10/22/2024 1:28 PM, Joe Damato wrote:
> I took another look at this to make sure that RTNL is held when
> igc_set_queue_napi is called after the e1000 bug report came in [1],
> and there may be two locations I've missed:
> 
> 1. igc_resume, which calls __igc_open
> 2. igc_io_error_detected, which calls igc_down
> 
> In both cases, I think the code can be modified to hold rtnl around
> calls to __igc_open and igc_down.
> 
> Let me know what you think ?
> 
> If you agree that I should hold rtnl in both of those cases, what is
> the best way to proceed:
>   - send a v4, or
>   - wait for this to get merged (since I got the notification it was
>     pulled into intel-next) and send a fixes ?
> 

Intel-next uses a stacked set of patches which we then send in batches
via PRs as they pass our internal testing.

We can drop the v3 and await v4.

> Here's the full analysis I came up with; I tried to be thorough, but
> it is certainly possible I missed a call site:
> 
> For the up case:
> 
> - igc_up:
>   - called from igc_reinit_locked, which is called via:
>     - igc_reset_task (rtnl is held)
>     - igc_set_features (ndo_set_features, which itself has an ASSERT_RTNL)
>     - various places in igc_ethtool (set_priv_flags, nway_reset,
>       ethtool_set_eee) all of which have RTNL held
>   - igc_change_mtu which also has RTNL held
> - __igc_open
>   - called from igc_resume, which may need an rtnl_lock ?
>   - igc_open
>     - called from igc_io_resume, rtnl is held
>     - called from igc_reinit_queues, only via ethool set_channels,
>       where rtnl is held
>     - ndo_open where rtnl is held
> 
> For the down case:
> 
> - igc_down:
>   - called from various ethtool locations (set_ringparam,
>     set_pauseparam, set_link_ksettings) all of which hold rtnl
>   - called from igc_io_error_detected, which may need an rtnl_lock
>   - igc_reinit_locked which is fine, as described above
>   - igc_change_mtu which is fine, as described above
>   - called from __igc_close
>     - called from __igc_shutdown which holds rtnl
>     - called from igc_reinit_queues which is fine as described above
>     - called from igc_close which is ndo_close

This analysis looks complete to me.