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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Sun, 8 Jul 2007 23:45:26 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Benjamin Herrenschmidt <benh@...nel.crashing.org>
Cc:	Alan Stern <stern@...land.harvard.edu>,
	Kyle Moffett <mrmacman_g4@....com>,
	Nigel Cunningham <nigel@...el.suspend2.net>,
	Pavel Machek <pavel@....cz>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	linux-kernel@...r.kernel.org, linux-pm@...ts.linux-foundation.org
Subject: Re: [PATCH] Remove process freezer from suspend to RAM pathway

On Sunday, 8 July 2007 23:03, Benjamin Herrenschmidt wrote:
> On Sun, 2007-07-08 at 21:15 +0200, Rafael J. Wysocki wrote:
> > On Sunday, 8 July 2007 07:14, Benjamin Herrenschmidt wrote:
> > [--snip--]
> > > 
> > > I just think that the freezer approach, as it is, is backward. We can't
> > > have a 3rd party try to discriminate what to freeze and what not, it
> > > will always get something wrong, and in some cases with the wrong timing
> > > or ordering.
> > 
> > Nice discussion, except for one thing: the freezer doesn't decide what to
> > freeze.  For example, even right now kernel threads decide if they want to be
> > frozen.
> 
> Somewhat... userspace doesn't and workqueues are a gray area.

Workqueues are kernel threads and the creator decides if they are going to
freeze.  There are only two freezable worqueues in the entire tree right now.

> Also, I've been thinking this "icebox" idea a bit more and it seems in
> fact a bit racy in some areas, at least for use by things like drivers,
> unless we end up doing something aking to an RCU on suspend, waiting for
> all tasks to reach userland once, but that has the same annoyances as
> the current freezer.
> 
> Thus I'm tempted to go back to saying that driver can handle things
> locally :-)

Actaully, I'm perfectly fine with that, as long as each task blocked by the
driver due to suspend has PF_FROZEN (or something similar) set.  Then, at
least theoretically, we'll be able to drop the freezer from the suspend code
path and move it after device_suspend() (or the hibernation-specific
equivalent) for hibernation (in that case there shouldn't be a problem with
any task waiting on I/O while the freezer is running ;-)).

Greetings,
Rafael


-- 
"Premature optimization is the root of all evil." - Donald Knuth
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/