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

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Date: Fri, 29 Dec 2023 04:08:24 +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 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?

Regards
Stanislaw