linux-kernel - Re: [PATCH v1 2/3] async: Introduce async_schedule_dev

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Date: Tue, 2 Jan 2024 08:09:51 +0100
From: Stanislaw Gruszka <stanislaw.gruszka@...ux.intel.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>,
	Greg KH <gregkh@...uxfoundation.org>, linux-pm@...r.kernel.org,
	Youngmin Nam <youngmin.nam@...sung.com>,
	linux-kernel@...r.kernel.org, d7271.choe@...sung.com,
	janghyuck.kim@...sung.com, hyesoo.yu@...sung.com,
	Alan Stern <stern@...land.harvard.edu>,
	Ulf Hansson <ulf.hansson@...aro.org>
Subject: Re: [PATCH v1 2/3] async: Introduce async_schedule_dev_nocall()

On Fri, Dec 29, 2023 at 05:36:01PM +0100, Rafael J. Wysocki wrote:
> On Fri, Dec 29, 2023 at 3:54 PM Stanislaw Gruszka
> <stanislaw.gruszka@...ux.intel.com> wrote:
> >
> > On Fri, Dec 29, 2023 at 02:37:36PM +0100, Rafael J. Wysocki wrote:
> > > > > +bool async_schedule_dev_nocall(async_func_t func, struct device *dev)
> > > > > +{
> > > > > +     struct async_entry *entry;
> > > > > +
> > > > > +     entry = kzalloc(sizeof(struct async_entry), GFP_KERNEL);
> > > >
> > > > Is GFP_KERNEL intended here ?
> > >
> > > Yes, it is.
> > >
> > > PM will be the only user of this, at least for now, and it all runs in
> > > process context.
> > >
> > > > I think it's not safe since will
> > > > be called from device_resume_noirq() .
> > >
> > > device_resume_noirq() runs in process context too.
> > >
> > > The name is somewhat confusing (sorry about that) and it means that
> > > hardirq handlers (for the majority of IRQs) don't run in that resume
> > > phase, but interrupts are enabled locally on all CPUs (this is
> > > required for wakeup handling, among other things).
> >
> > Then my concern would be: if among devices with disabled IRQs are
> > disk devices? Seems there are disk devices as well, and because
> > GFP_KERNEL can start reclaiming memory by doing disk IO (write
> > dirty pages for example), with disk driver interrupts disabled
> > reclaiming process can not finish.
> >
> > I do not see how such possible infinite waiting for disk IO
> > scenario is prevented here, did I miss something?
> 
> Well, it is not a concern, because the suspend code already prevents
> the mm subsystem from trying too hard to find free memory.  See the
> pm_restrict_gfp_mask() call in enter_state().

So that I missed :-) Thanks for explanations.

Reviewed-by: Stanislaw Gruszka <stanislaw.gruszka@...ux.intel.com> for the series.