linux-kernel - Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

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 for Android: free password hash cracker in your pocket

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

Date:	Thu, 27 May 2010 17:07:14 +0100
From:	Matthew Garrett <mjg59@...f.ucam.org>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Arve Hjønnevåg <arve@...roid.com>,
	Florian Mickler <florian@...kler.org>,
	Vitaly Wool <vitalywool@...il.com>,
	Peter Zijlstra <peterz@...radead.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Paul@...p1.linux-foundation.org, felipe.balbi@...ia.com,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	Linux PM <linux-pm@...ts.linux-foundation.org>
Subject: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

On Thu, May 27, 2010 at 04:05:43PM +0100, Alan Cox wrote:
> > Now, if the user is playing this game, you want it to be scheduled. If 
> > the user has put down their phone and the screen lock has kicked in, you 
> > don't want it to be scheduled. So we could imagine some sort of cgroup 
> > that contains untrusted tasks - when the session is active we set a flag 
> 
> I would hope not, because I'd rather prefer my app that used the screen
> to get the chance to save important data on what it was doing
> irrespective of the screen blank:  "I have an elegant proof for this
> problem but my battery has gone flat"

Perhaps set after callbacks are made. But given that the approach 
doesn't work anyway...

> What is the problem here - your device driver for the display can block
> tasks it doesn't want to use the display.

It's still racy. Going back to my example without any of the suspend 
blocking code, but using a network socket rather than an input device:

int input = socket(AF_INET, SOCK_STREAM|SOCK_NONBLOCK, 0);
char foo;
struct sockaddr addr;
connect (input, &addr, sizeof(addr))
while (1) {
       if (read(input, &foo, 1) > 0) {
               (do something)
       } else {
               (draw bouncing cows and clouds and tractor beams briefly)
       }
}

A network packet arrives while we're drawing. Before we finish drawing, 
the policy timeout expires and the screen turns off. The app's drawing 
is blocked and so never gets to the point of reading the socket. The 
wakeup event has been lost.

-- 
Matthew Garrett | mjg59@...f.ucam.org
--
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/