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

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Message-Id: <E1I6Y5o-0001qm-00@dorka.pomaz.szeredi.hu>
Date:	Thu, 05 Jul 2007 22:38:24 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	rjw@...k.pl
CC:	miklos@...redi.hu, oliver@...kum.org, pavel@....cz,
	paulus@...ba.org, stern@...land.harvard.edu,
	johannes@...solutions.net, linux-pm@...ts.linux-foundation.org,
	linux-kernel@...r.kernel.org, mjg59@...f.ucam.org,
	benh@...nel.crashing.org
Subject: Re: [linux-pm] Re: [PATCH] Remove process freezer from suspend to RAM pathway

> > > > > > Actually fuse allows SIGKILL, because it's always fatal, and the
> > > > > > syscall may not be restarted.
> > > > > 
> > > > > I think you want to stick try_to_freeze() at the same places where you
> > > > > do SIGKILL handling. That should solve the 'syslogd is unfreezeable'
> > > > > problem.
> > > > 
> > > > I could, but it would not solve the general problem.  Namely, that the
> > > > presence of fuse imposes a certain ordering in which userspace tasks
> > > > have to be frozen.  And it is not possible to know this ordering.
> > > 
> > > Actually, why do you need this? There is no absolute need that you
> > > finish the request. You must either finish the request or let yourself
> > > be frozen.
> > > 
> > > A quick look through fuse reveals principally request_wait_answer()
> > > And maybe a few other places. Is there some hidden reason you cannot
> > > handle being frozen here?
> > 
> > Yes, fuse could handle being frozen there.  However that would only
> > solve part of the problem: an operation waiting for a reply could be
> > holding a VFS mutex and some other task may be blocked on that mutex.
> > 
> > How would you solve freezing those tasks?
> 
> How probable is this situation?

I guess it depends on usage patterns.

I don't remember seeing any such cases, even though I have a permanent
fuse mount, and I suspend regularly.  But the fs is probably totally
idle during suspend in my case.

But some people use fuse as a home or root filesystem and in those
cases it can become quite likely to cause problems.

Miklos
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