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Date:	Thu, 22 Mar 2007 00:53:54 +0100
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Maxim <maximlevitsky@...il.com>
Cc:	linux-kernel@...r.kernel.org, Pavel Machek <pavel@....cz>
Subject: Re: [BUG] Code reordering in swsusp breaks suspend on SMP systems

On Thursday, 22 March 2007 00:39, Maxim wrote:
> On Thursday 22 March 2007 01:24:25 Rafael J. Wysocki wrote:
> > On Thursday, 22 March 2007 00:09, 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,
> > 
> > Could you please sent this information to the list?  I'd like it to reach all
> > of the CCed parites. ;-)
> 
> I did now ( sorry I just keep using this Answer command, instead of Answer to everybody)
> I didn't intend to send private email.
> > 
> > > 	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
> > 
> > This is interesting.  Did it happen before or is it a regression?
> 
> It is from the same group of bugs , I mean hang because cpu_up/down is called with frozen tasks
> Of course it didn't happen before those reordering commits were introduced

Well, we want cpu_up/down to be called after processes have been frozen, for
various reasons (one of them being that applications shouldn't see us playing
with the CPUs).

Thanks for reporting this, I'll have a look at the microcode update driver.

> > > 	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.  We've had such reports earlier, but I think the problem is still unresolved.  Any
> > additional information will be valuable.
> 
> I will do my best,
> Also I want to note that the above problem is 100% repeatable, and happens independently whenever suspend to disk
> or suspend to ram was used in first successful try ( or at least, I got back-trace using kdb, after suspend to disk, after
> suspend to ram system hang, so I assume, that this it is same problem , because it didn't hang of first try)

Thanks for the information.

BTW, what's the last kernel you have tested?

Rafael
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