Re: [RFC 5/5] pm: remove kernel thread freezing

[Dave Chinner <david@fromorbit.com>]

On Tue, Oct 03, 2017 at 11:53:13AM -0700, Luis R. Rodriguez wrote:
> Now that all filesystems which used to rely on kthread
> freezing have been converted to filesystem freeze/thawing
> we can remove the kernel kthread freezer.

Really? There's no other subsystem that relies on kernel thread
and workqueue freezing to function correctly on suspend?

> -/**
> - * freeze_kernel_threads - Make freezable kernel threads go to the refrigerator.
> - *
> - * On success, returns 0.  On failure, -errno and only the kernel threads are
> - * thawed, so as to give a chance to the caller to do additional cleanups
> - * (if any) before thawing the userspace tasks. So, it is the responsibility
> - * of the caller to thaw the userspace tasks, when the time is right.
> - */
> -int freeze_kernel_threads(void)
> -{
> -	int error;
> -
> -	pr_info("Freezing remaining freezable tasks ... ");
> -
> -	pm_nosig_freezing = true;
> -	error = try_to_freeze_tasks(false);

This freezes workqueues as well as kernel threads, so this affects
any subsystem that uses WQ_FREEZABLE. A quick glance tells me this
includes graphics drivers, spi devices, usb hubs, power management,
and a few filesystems, too.

> -	if (!error)
> -		pr_cont("done.");
> -
> -	pr_cont("\n");
> -	BUG_ON(in_atomic());
> -
> -	if (error)
> -		thaw_kernel_threads();
> -	return error;
> -}
> -
>  void thaw_processes(void)
>  {
>  	struct task_struct *g, *p;
> @@ -234,23 +207,3 @@ void thaw_processes(void)
>  	pr_cont("done.\n");
>  	trace_suspend_resume(TPS("thaw_processes"), 0, false);
>  }
> -
> -void thaw_kernel_threads(void)
> -{
> -	struct task_struct *g, *p;
> -
> -	pm_nosig_freezing = false;
> -	pr_info("Restarting kernel threads ... ");
> -
> -	thaw_workqueues();

And this is where the workqueues are thawed.

So I doubt we can safely remove all this code like this...

Cheers,

Dave.
-- 
Dave Chinner
david@fromorbit.com