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

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Date:	Thu, 5 Jul 2007 12:02:58 +0200
From:	Oliver Neukum <oliver@...kum.org>
To:	Miklos Szeredi <miklos@...redi.hu>
Cc:	paulus@...ba.org, stern@...land.harvard.edu,
	johannes@...solutions.net, rjw@...k.pl,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	pavel@....cz, mjg59@...f.ucam.org, benh@...nel.crashing.org
Subject: Re: [linux-pm] Re: [PATCH] Remove process freezer from suspend to RAM pathway

Am Donnerstag, 5. Juli 2007 schrieb Miklos Szeredi:
> > > And teach VFS to block suspension, while waiting on a mutex held by
> > > another process performing a fuse operation.
> > > 
> > > I can already hear the beautiful praise from Al Viro at the sight of
> > > that ;)
> > 
> > There is that.
> > 
> > OK, bite the bullet. Tasks involved in fuse are special. Give them a flag
> > and teach the freezer to put them on ice only after all other task are
> > frozen. In a way they are kernel, there's no use denying that.
> 
> And flag every other process, that the flagged process is
> communicating with?  How are you proposing to do that?
> 
> Quoting Paul:
> 
> "1. The freezer cannot be guaranteed deadlock-free without constructing
>    a dependency graph between tasks (both user and kernel), which is
>    virtually impossible since the dependencies are not externally
>    observable."

A deadlock requires that the circular wait is uninterruptible. Normal IPC
isn't.

What are you doing in the userland portions of fuse? Some kind of IPC
with other tasks? There is a limit to which you can push kernel functionality
into user space.

	Regards
		Oliver

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