netdev - Re: cpu_rmap maps CPUs to wrong interrupts after reprogramming affinities

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <d36de97f4a1ff574b8ac1f530af550fab5331480.camel@decadent.org.uk>
Date: Thu, 19 Dec 2024 23:04:55 +0100
From: Ben Hutchings <ben@...adent.org.uk>
To: Caleb Sander <csander@...estorage.com>, David Miller
 <davem@...emloft.net>,  Tom Herbert <therbert@...gle.com>, Thomas Gleixner
 <tglx@...utronix.de>, Eli Cohen <elic@...dia.com>,  Jakub Kicinski	
 <kuba@...nel.org>, Eric Dumazet <edumazet@...gle.com>, Paolo Abeni	
 <pabeni@...hat.com>
Cc: netdev@...r.kernel.org, Linux Kernel Mailing List
	 <linux-kernel@...r.kernel.org>
Subject: Re: cpu_rmap maps CPUs to wrong interrupts after reprogramming
 affinities

On Fri, 2024-12-13 at 10:18 -0800, Caleb Sander wrote:
> Hi netdev,
> While testing ARFS, we found set_rps_cpu() was calling
> ndo_rx_flow_steer() with an RX queue that was not affinitized to the
> desired CPU. The issue occurred only after modifying interrupt
> affinities. It looks to be a bug in cpu_rmap, where cpu_rmap_update()
> can leave CPUs mapped to interrupts which are no longer the most
> closely affinitized to them.
> 
> Here is the simplest scenario:
> 1. A network device has 2 IRQs, 1 and 2. Initially only CPU A is
> available to process the network device. So both IRQs 1 and 2 are
> affinitized to CPU A.
[...]

This seems like a misconfiguration: there shouldn't be more RX queues
than CPUs to handle them.  I probably never considered it when
implementing cpu_rmap.  Still, I agree that this could happen as a
transitory state, and the reverse-map ought to become sensible once all
the RX queues are assigned to different CPUs.

But I haven't looked at that code for over a decade, so I'm probably
not the right person to address this now.

Ben.

-- 
Ben Hutchings
The world is coming to an end.	Please log off.


Download attachment "signature.asc" of type "application/pgp-signature" (834 bytes)