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

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Message-Id: <200707050853.42224.oliver@neukum.org>
Date:	Thu, 5 Jul 2007 08:53:41 +0200
From:	Oliver Neukum <oliver@...kum.org>
To:	Pavel Machek <pavel@....cz>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	linux-kernel@...r.kernel.org, linux-pm@...ts.linux-foundation.org,
	Nigel Cunningham <nigel@...el.suspend2.net>
Subject: Re: [PATCH] Remove process freezer from suspend to RAM pathway

Am Donnerstag, 5. Juli 2007 schrieb Pavel Machek:
> On Tue 2007-07-03 19:20:59, Oliver Neukum wrote:
> > Am Dienstag, 3. Juli 2007 schrieb Rafael J. Wysocki:
> > > On Tuesday, 3 July 2007 15:08, Rafael J. Wysocki wrote:
> > > > On Tuesday, 3 July 2007 07:51, Benjamin Herrenschmidt wrote:
> > > > > On Tue, 2007-07-03 at 05:29 +0100, Matthew Garrett wrote:
> > > > > > Suspend to RAM on a machine with / on a fuse filesystem turns out to be 
> > > > > > a screaming nightmare - either the suspend fails because syslog (for 
> > > > > > instance) can't be frozen, or the machine deadlocks for some other 
> > > > > > reason I haven't tracked down. We could "fix" fuse, or alternatively we 
> > > > > > could do what we do for suspend to RAM on other platforms (PPC and APM) 
> > > > > > and just not use the freezer.
> > > > > 
> > > > > The main reason for deadlocks is because we do a sys_sync() after the
> > > > > freeze, which we shouldn't do.
> > > > 
> > > > So why don't we remove the sys_sync() from freeze_processes() instead?
> > > 
> > > The patch follows (untested).
> > > 
> > > Greetings,
> > > Rafael
> > > 
> > > 
> > > ---
> > > From: Rafael J. Wysocki <rjw@...k.pl>
> > > 
> > > We shouldn't sync filesystems from within the freezer, because it's not needed
> > > for suspend to RAM and leads to problems with FUSE.
> > 
> > This seems fishy. Swsusp needs enough clean memory to make enough
> > room for the image. If you sync before you freeze, the running tasks can
> > redirty memory.
> > What makes you sure that you don't die as shrink_all_memory() writes out
> > pages?
> 
> Shrink_all_memory should just free enough memory, what's the problem?
> Yes, we can have dirty memory, shrink_all_memory() can write that out
> just fine.

If there's any dirty memory to be written out through fuse, this will not
work as user space is already frozen. Now I am told that with fuse writes
are synchronous. Therefore I don't understand why having a call to sys_sync()
can make a difference. IMHO removing it to make fuse work covers over
a symptom but hides the bug.

	Regards
		Oliver

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