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

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Date: Fri, 29 Dec 2023 14:37:36 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Stanislaw Gruszka <stanislaw.gruszka@...ux.intel.com>
Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>, Greg KH <gregkh@...uxfoundation.org>, 
	linux-pm@...r.kernel.org, Youngmin Nam <youngmin.nam@...sung.com>, rafael@...nel.org, 
	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 8:02 AM Stanislaw Gruszka
<stanislaw.gruszka@...ux.intel.com> wrote:
>
> On Wed, Dec 27, 2023 at 09:38:23PM +0100, Rafael J. Wysocki wrote:
> > From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> >
> > In preparation for subsequent changes, introduce a specialized variant
> > of async_schedule_dev() that will not invoke the argument function
> > synchronously when it cannot be scheduled for asynchronous execution.
> >
> > The new function, async_schedule_dev_nocall(), will be used for fixing
> > possible deadlocks in the system-wide power management core code.
> >
> > Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
> > ---
> >  drivers/base/power/main.c |   12 ++++++++----
> >  include/linux/async.h     |    2 ++
> >  kernel/async.c            |   29 +++++++++++++++++++++++++++++
> >  3 files changed, 39 insertions(+), 4 deletions(-)
> >
> > Index: linux-pm/kernel/async.c
> > ===================================================================
> > --- linux-pm.orig/kernel/async.c
> > +++ linux-pm/kernel/async.c
> > @@ -244,6 +244,35 @@ async_cookie_t async_schedule_node(async
> >  EXPORT_SYMBOL_GPL(async_schedule_node);
> >
> >  /**
> > + * async_schedule_dev_nocall - A simplified variant of async_schedule_dev()
> > + * @func: function to execute asynchronously
> > + * @dev: device argument to be passed to function
> > + *
> > + * @dev is used as both the argument for the function and to provide NUMA
> > + * context for where to run the function.
> > + *
> > + * If the asynchronous execution of @func is scheduled successfully, return
> > + * true. Otherwise, do nothing and return false, unlike async_schedule_dev()
> > + * that will run the function synchronously then.
> > + */
> > +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).