linux-kernel - Re: [PATCH] Fix failure to resume from initrds.

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Message-Id: <200709112341.21225.nigel@nigel.suspend2.net>
Date:	Tue, 11 Sep 2007 23:41:20 +1000
From:	Nigel Cunningham <nigel@...el.suspend2.net>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	nigel@...pend2.net, LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Pavel Machek <pavel@....cz>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [PATCH] Fix failure to resume from initrds.

Hi.

On Tuesday 11 September 2007 23:23:32 Rafael J. Wysocki wrote:
> On Tuesday, 11 September 2007 15:12, Rafael J. Wysocki wrote:
> > On Tuesday, 11 September 2007 13:55, Rafael J. Wysocki wrote:
> > > On Tuesday, 11 September 2007 13:27, Nigel Cunningham wrote:
> > > > Hi.
> > > > 
> > > > On Tuesday 11 September 2007 21:04:22 Rafael J. Wysocki wrote:
> > > > > On Tuesday, 11 September 2007 05:54, Nigel Cunningham wrote:
> > > > > > Hi all.
> > > > > > 
> > > > > > Commit 831441862956fffa17b9801db37e6ea1650b0f69 (Freezer: make 
kernel 
> > > > threads
> > > > > > nonfreezable by default) breaks freezing when attempting to resume 
from an
> > > > > > initrd, because the init (which is freezeable) spins while waiting 
for 
> > > > another
> > > > > > thread to run /linuxrc, but doesn't check whether it has been told 
to 
> > > > enter
> > > > > > the refrigerator.
> > > > > 
> > > > > Hm.
> > > > > 
> > > > > I use a resume from an initrd on a regular basis and it works 
without the 
> > > > patch
> > > > > below.
> > > > > 
> > > > > I think we need to investigate what happens in your test case a bit.
> > > > 
> > > > Ah. That makes me realise that I see that too - my AMD64 uniprocessor 
laptop 
> > > > didn't need the patch (guess that's why I didn't notice the need and 
ack'd 
> > > > the patch). But my x86 SMP machine... it needs this. I'll see if 
they're 
> > > > running on different processors.
> > > 
> > > Well, strange.  My x86_64 SMP machines don't need the patch too.
> > 
> > Anyway, yes, init is freezable, but should it be?
> > 
> > I mean, shouldn't we rather add PF_NOFREEZE to kernel_init()?
> 
> Argh, no.  PF_NOFREEZE is inherited by the children.
> 
> So, I think that your patch is correct, but there's some suspend2-specific
> stuff in it.  I've rediffed it against 2.6.23-rc6 and moved try_to_freeze()
> before yield().

Ah yeah. Sorry about that. Is there some reason I've forgotten that makes the 
order of try_to_freeze & yield in a loop like this matter?

By the way, I had a go at getting fuse processes frozen today. Seems to be 
doable if you take a freeze filesystems prior to processes approach. I've got 
a lot more testing and a bit of cleaning up to do before I'd want to show it 
to anyone, but did successfully do cycles with sshfs, fuseiso and curlftpfs. 
Of course I don't seriously expect it to get merged - everyone's too much in 
love with kexec at the moment :)

Regards,

Nigel
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