netdev - Re: [WIP v2] igc: fix deadlock caused by taking RTNL in RPM resume path

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Date:   Thu, 11 Aug 2022 22:41:48 +0100
From:   James Hogan <jhogan@...nel.org>
To:     Vinicius Costa Gomes <vinicius.gomes@...el.com>
Cc:     Vinicius Costa Gomes <vinicius.gomes@...el.com>,
        Paul Menzel <pmenzel@...gen.mpg.de>,
        Tony Nguyen <anthony.l.nguyen@...el.com>,
        Jesse Brandeburg <jesse.brandeburg@...el.com>,
        netdev@...r.kernel.org, intel-wired-lan@...ts.osuosl.org,
        Sasha Neftin <sasha.neftin@...el.com>,
        Aleksandr Loktionov <aleksandr.loktionov@...el.com>
Subject: Re: [WIP v2] igc: fix deadlock caused by taking RTNL in RPM resume path

On Thursday, 11 August 2022 21:25:24 BST Vinicius Costa Gomes wrote:
> It was reported a RTNL deadlock in the igc driver that was causing
> problems during suspend/resume.
> 
> The solution is similar to commit ac8c58f5b535 ("igb: fix deadlock
> caused by taking RTNL in RPM resume path").
> 
> Reported-by: James Hogan <jhogan@...nel.org>
> Signed-off-by: Vinicius Costa Gomes <vinicius.gomes@...el.com>
> ---
> Sorry for the noise earlier, my kernel config didn't have runtime PM
> enabled.

Thanks for looking into this.

This is identical to the patch I've been running for the last week. The 
deadlock is avoided, however I now occasionally see an assertion from 
netif_set_real_num_tx_queues due to the lock not being taken in some cases via 
the runtime_resume path, and a suspicious rcu_dereference_protected() warning 
(presumably due to the same issue of the lock not being taken). See here for 
details:
https://lore.kernel.org/netdev/4765029.31r3eYUQgx@saruman/

Cheers
James