linux-kernel - Re: [linux-pm] Re: [PATCH] Remove process freezer from suspend to RAM pathway

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Date:	Fri, 06 Jul 2007 08:59:52 +1000
From:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Paul Mackerras <paulus@...ba.org>,
	Johannes Berg <johannes@...solutions.net>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Linux-pm mailing list <linux-pm@...ts.linux-foundation.org>,
	Kernel development list <linux-kernel@...r.kernel.org>,
	Pavel Machek <pavel@....cz>,
	Matthew Garrett <mjg59@...f.ucam.org>
Subject: Re: [linux-pm] Re: [PATCH] Remove process freezer from suspend to
	RAM pathway

On Thu, 2007-07-05 at 10:23 -0400, Alan Stern wrote:
> 
> How will that help?  Block the kernel thread in the freezer or block it 
> in the driver -- either way it is blocked.  So how do your deadlocks 
> get resolved?

Because nobody is waiting on that kernel thread anyway without a freezer
so there is no deadlock anymore.

> I disagree with your analysis -- not that it's completely wrong, but it 
> points out an existing basic problem in the kernel.  The kernel should 
> never depend on userspace!  More correctly, a task executing in the 
> kernel should never block with any sort of mutex or other lock held (in 
> a way that would preclude it from being frozen, let's say) while 
> waiting for a response from userspace.
> 
> Then the dependency graph would be easy to construct: User tasks can
> depend on whatever they want, and kernel threads never depend on a user
> task.

In an idea world, there would be no hunger...

> If this contradicts the existing implementations and APIs for userspace 
> filesystems, then so be it.  My conclusion would be that the 
> implementations and APIs should be changed.

Why are you guys working so hard and spending so much energy to try to
avoid doing the right thing is beyond my understanding...

> It _does_ apply to kernel threads.  That's exactly why I wrote above 
> that kernel threads which try to do I/O during a suspend will need 
> extra attention.

Ok none at all if you don't have a freezer.

Ben.


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