linux-kernel - Re: [PATCH 03/27] PCI: Protect against concurrent change of housekeeping cpumask

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Message-ID: <aF1eYIkUA6k60kTK@localhost.localdomain>
Date: Thu, 26 Jun 2025 16:51:12 +0200
From: Frederic Weisbecker <frederic@...nel.org>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Marco Crivellari <marco.crivellari@...e.com>,
	Michal Hocko <mhocko@...e.com>,
	Peter Zijlstra <peterz@...radead.org>, Tejun Heo <tj@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Vlastimil Babka <vbabka@...e.cz>, Waiman Long <longman@...hat.com>
Subject: Re: [PATCH 03/27] PCI: Protect against concurrent change of
 housekeeping cpumask

Le Fri, Jun 20, 2025 at 11:17:10AM -0500, Bjorn Helgaas a écrit :
> On Fri, Jun 20, 2025 at 05:22:44PM +0200, Frederic Weisbecker wrote:
> > HK_TYPE_DOMAIN will soon integrate cpuset isolated partitions and
> > therefore be made modifyable at runtime. Synchronize against the cpumask
> > update using appropriate locking.
> 
> s/modifyable/modifiable/
> 
> > Queue and wait for the PCI call to complete while holding the
> > housekeeping rwsem. This way the housekeeping update side doesn't need
> > to propagate its changes to PCI.
> 
> What PCI call are we waiting for?  I see housekeeping_lock(), but I
> assume that's doing some housekeeping-related mutual exclusion, not
> waiting for PCI work.

It's waiting for the call to work_on_cpu() to complete (along with
the CPU election through housekeeping_cpumask()).

> 
> I don't know how to use housekeeping_lock() or when it's needed.  Can
> you add some guidance here and at the housekeeping_lock() definition?

You're right, it's missing documentation, context and guidance. I'll
try to fill that in the next iteration. Also the lock is likely going
to be replaced by RCU instead.

Thanks.

-- 
Frederic Weisbecker
SUSE Labs