linux-kernel - Re: [BUG] Code reordering in swsusp breaks suspend on SMP systems

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Date:	Thu, 22 Mar 2007 01:18:56 +0200
From:	Maxim <maximlevitsky@...il.com>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	linux-kernel@...r.kernel.org, Pavel Machek <pavel@....cz>,
	nigel@...el.suspend2.net
Subject: Re: [BUG] Code reordering in swsusp breaks suspend on SMP systems

On Thursday 22 March 2007 01:09:54 Maxim wrote:
> On Thursday 22 March 2007 00:39:02 you wrote:
> > On Wednesday, 21 March 2007 23:21, Pavel Machek wrote:
> > > Hi!
> > > 
> > > > Starting with 2.6.21-rc1 suspend to ram and disk doesn't work anymore on my system.
> > > > 
> > > > I did a git-bisect and found that those commits break it:
> > > > 
> > > > e3c7db621bed4afb8e231cb005057f2feb5db557 - [PATCH] [PATCH] PM: Change code ordering in main.c
> > > > ed746e3b18f4df18afa3763155972c5835f284c5 - [PATCH] [PATCH] swsusp: Change code ordering in disk.c
> > > > 259130526c267550bc365d3015917d90667732f1 - [PATCH] [PATCH] swsusp: Change code ordering in user.c
> > > > 
> > > 
> > > (Yep, it was in my "to analyze" queue).
> > > 
> > > > I already reported about it, but now i know the reason why suspend breaks.
> > > > 
> > > > The problem is that both cpu_up/cpu_down were allowed to sleep until now, 
> > > > and it did work because those functions could be called only in process context
> > > > (the one that writes to /sys/devices/system/cpu/cpu*/online) or  idle thread  that does smp_init()).
> > > > 
> > > > But now they are called _after_ all tasks were suspended, so if cpu_down tries for example to take a lock
> > > > that is taken by different process, it can't since the different proccess is frozen and can't release the lock.
> > > > 
> > > 
> > > Thanks for detailed explanation.
> > > 
> > > ...but, on my machine suspend works ok in -rc4. I'm not seeing this.
> > > 
> > > ...by design, "frozen" tasks must not hold any locks. If frozen task
> > > holds a lock, that's a bug.
> > > 
> > > > Or, it is also possible to revert this change.
> > > 
> > > Are you using xfs?
> > 
> > Well, this is the only case that can trigger it.  There are no other freezable
> > workqueues.
> > 
> > Greetings,
> > Rafael
> > 
> 
> Hello,
> 
> 	Yes, you are right and it is XFS
> 
> 	System suspends and resumes with xfs and your patch correctly,
> 
> 	Of course I need to mention that I had to unload microcode update driver because it prevented resume,
> 	because it calls firmware loader helper, and again sleeps on lock
> 
> 	And also I noticed now that system oopses on second attempt to suspend ether to ram or disk
> 	in pci_restore_msi_state which is called indirectly by ahci_pci_device_resume, I will investigate this soon.
> 
> 	Thanks a lot,
> 		Regards,
> 			Maxim Levitsky
> 
> 

And I forgot to cc here too, I didn't intend to send private email.

	Regards,
		Maxim Levitsky
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