linux-kernel - Re: [PATCH 02/33] PCI: Protect against concurrent change of housekeeping cpumask

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Message-ID: <aNJjZ9ouRSkkyyxU@2a01cb069018a810e4ede1071806178f.ipv6.abo.wanadoo.fr>
Date: Tue, 23 Sep 2025 11:07:51 +0200
From: Frederic Weisbecker <frederic@...nel.org>
To: Waiman Long <llong@...hat.com>
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>, linux-pci@...r.kernel.org
Subject: Re: [PATCH 02/33] PCI: Protect against concurrent change of
 housekeeping cpumask

Le Mon, Sep 22, 2025 at 05:51:39PM -0400, Waiman Long a écrit :
> On 9/18/25 10:00 AM, Frederic Weisbecker wrote:
> > No the point is that I need to keep the target selection
> > (housekeeping_cpumask() read) and the work queue within the same
> > RCU critical section so that things are synchronized that way:
> > 
> >      CPU 0                                          CPU 1
> >      -----                                          -----
> >      rcu_read_lock()                                housekeeping_update()
> >      cpu = cpumask_any(housekeeping_cpumask(...))       housekeeping_cpumask &= ~val
> >      queue_work_on(cpu, pci_probe_wq, work)             synchronize_rcu()
> >      rcu_read_unlock()                                  flush_workqueue(pci_probe_wq)
> >      flush_work(work)
> > And I can't include the whole work_on_cpu() within rcu_read_lock() because
> > flush_work() may sleep.
> 
> Right, you are trying to avoid flush_work() within rcu_read_lock() critical
> section. It makes it easier to review if you mention that in the commit log.

Good point!

> 
> > 
> > Also now that you mention it, I need to create that pci_probe_wq and flush it :-)
> 
> OK, another wq :-)

Yeah I know :-s

> 
> Cheers,
> Longman
> 

-- 
Frederic Weisbecker
SUSE Labs