linux-kernel - Re: [BUGFIX] PM: Fix active child counting when disabled and forbidden

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:	Mon, 12 Nov 2012 08:37:29 +0800
From:	Huang Ying <ying.huang@...el.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	"Rafael J. Wysocki" <rjw@...k.pl>, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org
Subject: Re: [BUGFIX] PM: Fix active child counting when disabled and
 forbidden

On Fri, 2012-11-09 at 11:41 -0500, Alan Stern wrote:
> On Fri, 9 Nov 2012, Huang Ying wrote:
> 
> > On Thu, 2012-11-08 at 12:07 -0500, Alan Stern wrote:
> > > On Thu, 8 Nov 2012, Rafael J. Wysocki wrote:
> > > 
> > > > > > > is it a good idea to allow to set device state to SUSPENDED if the device
> > > > > > > is disabled?
> > > > > > 
> > > > > > No, it is not.  The status should always be ACTIVE as long as usage_count > 0.
> > > 
> > > That isn't strictly true, because pm_runtime_get_noresume violates this
> > > rule.  What the PM core actually does is prevent a transition from the
> > > ACTIVE state to the SUSPENDING/SUSPENDED state if usage_count > 0,
> > > _provided_ runtime PM is enabled.  There's no such restriction when it
> > > is disabled.
> > 
> > Usage count may be not a issue for the end user.  But "on" in "control"
> > sysfs file + SUSPENDED can be confusing for the end user.  Maybe we need
> > to check dev->power.runtime_auto in pm_runtime_set_suspended().
> 
> You are confusing the issue by raising two separate (though related)
> questions.

Thanks for clarify.

> The first question: How should the PCI subsystem prevent the parents of 
> driverless VGA devices from being runtime suspended while userspace is 
> accessing them?

I think Rafael's patch is good for that.

> The second question: Should the PM core allow devices that are disabled
> for runtime PM to be in the SUSPENDED state when
> dev->power.runtime_auto is clear?

I think that should not be allowed.

> Assuming we don't want to allow this, there's a third question: Should
> pm_runtime_allow call pm_runtime_set_suspended if the device is
> disabled?

Is it absolute necessary to call pm_runtime_set_suspended?  If the
device is disabled, the transition to SUSPENDED state will not be
triggered even if the device is ACTIVE.

Best Regards,
Huang Ying


--
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/