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

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Message-Id: <E1I5mKv-0004TM-00@dorka.pomaz.szeredi.hu>
Date:	Tue, 03 Jul 2007 19:38:49 +0200
From:	Miklos Szeredi <miklos@...redi.hu>
To:	rjw@...k.pl
CC:	johannes@...solutions.net, stern@...land.harvard.edu,
	linux-pm@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
	pavel@....cz, mjg59@...f.ucam.org, paulus@...ba.org
Subject: Re: [linux-pm] Re: [PATCH] Remove process freezer from suspend to RAM pathway

> > Indeed. Actually, one could argue that it's impossible to solve the
> > problem as long as we try to call out to userspace during suspend and
> > need to wait until that's finished, like in the case of sys_sync() and
> > fuse filesystems, and probably other cases. Maybe we should make *those*
> > calls return a failure so that the suspend isn't transparent inside the
> > kernel but is transparent to userspace.
> 
> Well, it generally needs more consideration. :-)
> 
> I think that we should introduce mechanisms that will allow us to notify all
> kernel subsystems, including FUSE and similar, that the system is going to
> enter a sleep state (one of those is the notifier chain introduced recently).

Ugh, please no.

Believe me, fuse is doing _nothing_ out of the ordinary, and should
not need special treatment during suspend/resume.  If suspend itself
is doing something that triggers fuse activity, then that's a bug,
such as the sync() thing that started this thread.

> Then, they may react to such a notification by entering a "suspend" mode
> of operation in which they will return errors from some callbacks that
> otherwise should have succeeded etc.  That depends on the subsystem in
> question.

Sounds horrible.

Why do we need to deal with subsystem interdependencies during
suspend?  Isn't it about saving device state to ram?  That definitely
_should not_ need to trigger anything that touches filesystems or
other subsystems.

Miklos
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