linux-kernel - Re: [PATCH 1/1] PM / Runtime: let rpm_resume fail if rpm disabled and device suspended.

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]

Message-ID: <Pine.LNX.4.44L0.1406171007000.1187-100000@iolanthe.rowland.org>
Date:	Tue, 17 Jun 2014 10:11:32 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...ysocki.net>
cc:	Allen Yu <alleny@...dia.com>, Pavel Machek <pavel@....cz>,
	Len Brown <len.brown@...el.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	<linux-pm@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/1] PM / Runtime: let rpm_resume fail if rpm disabled
 and device suspended.

On Mon, 16 Jun 2014, Rafael J. Wysocki wrote:

> > For reasons having nothing to do with Allen's suggested change, I
> > wonder if we shouldn't replace this line with something like:
> > 
> > -	else if (dev->power.disable_depth == 1 && dev->power.is_suspended
> > +	else if (dev->power.disable > 0 && !dev->power.is_suspended
> > 	    && dev->power.runtime_status == RPM_ACTIVE)
> > 		retval = 1;
> > 
> > It seems that I've been bitten by this several times in the past.  
> > When a device is disabled for runtime PM, and more or less permanently
> > stuck in the RPM_ACTIVE state, calls to pm_runtime_resume() or
> > pm_runtime_get_sync() shouldn't fail.
> > 
> > For example, suppose some devices of a certain type support runtime 
> > power management but others don't.  We naturally want to call 
> > pm_runtime_disable() for the ones that don't.  But we also want the 
> > same driver to work for all the devices, which means that 
> > pm_runtime_get_sync() should return success -- otherwise the driver 
> > will think that something has gone wrong.
> > 
> > Rafael, what do you think?
> 
> That condition is there specifically to take care of the system suspend
> code path.  It means that if runtime PM is disabled, but it only has been
> disabled by the system suspend code path, we should treat the device as
> "active" (ie. return 1).  That won't work after the proposed change.

Ah, yes, quite true.  Okay, suppose we replace that line with just:

+	else if (dev->power.disable > 0

> I guess drivers that want to work with devices where runtime PM may be
> disabled can just check the return value of rpm_resume() for -EACCES?

They could, but it's extra work and it's extremely easy to forget 
about.  I'd prefer not to do things that way.

Alan Stern

--
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/