linux-kernel - Re: 2.6.22-rc1: Broken suspend on SMP with tifm

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Message-ID: <20070513203039.GA3143@tv-sign.ru>
Date:	Mon, 14 May 2007 00:30:39 +0400
From:	Oleg Nesterov <oleg@...sign.ru>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Michal Piotrowski <michal.k.k.piotrowski@...il.com>,
	Alex Dubov <oakad@...oo.com>, Pierre Ossman <drzeus@...eus.cx>
Subject: Re: 2.6.22-rc1: Broken suspend on SMP with tifm

On 05/14, Oleg Nesterov wrote:
>
> On 05/13, Rafael J. Wysocki wrote:
> > 
> > The suspend/hibernation is broken on SMP due to:
> > 
> > commit 3540af8ffddcdbc7573451ac0b5cd57a2eaf8af5
> > tifm: replace per-adapter kthread with freezeable workqueue
> > 
> > Well, it looks like freezable worqueues still deadlock with CPU hotplug
> > when worker threads are frozen.
> 
> Ugh. I thought we deprecated create_freezeable_workqueue(), exactly
> because suspend was changed to call _cpu_down() after freeze().
> 
> It is not that "looks like freezable worqueues still deadlock", it
> is "of course, freezable worqueues deadlocks" on CPU_DEAD.
> 
> The ->freezeable is still here just because of incoming "cpu-hotplug
> using freezer" rework.
> 
> No?
> 
> > --- linux-2.6.22-rc1.orig/kernel/workqueue.c
> > +++ linux-2.6.22-rc1/kernel/workqueue.c
> > @@ -799,9 +799,7 @@ static int __devinit workqueue_cpu_callb
> >  	struct cpu_workqueue_struct *cwq;
> >  	struct workqueue_struct *wq;
> >  
> > -	action &= ~CPU_TASKS_FROZEN;
> > -
> > -	switch (action) {
> > +	switch (action & ~CPU_TASKS_FROZEN) {
> 
> Confused. How can we see, say CPU_UP_PREPARE_FROZEN, if we cleared
> CPU_TASKS_FROZEN bit?

So, unless I missed something stupid, this patch is not 100% right.

I think the better fix (at least for now) is

	- #define create_freezeable_workqueue(name) __create_workqueue((name), 0, 1)
	+ #define create_freezeable_workqueue(name) __create_workqueue((name), 1, 1)

Alex, do you really need a multithreaded wq?

Rafael, what do you think?

Oleg.

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