linux-kernel - Re: [PATCH] PCI / PM: Block races between runtime PM and system sleep

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Date:	Thu, 23 Jun 2011 17:02:36 -0400 (EDT)
From:	Alan Stern <stern@...land.harvard.edu>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
cc:	Linux PM mailing list <linux-pm@...ts.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>
Subject: Re: [PATCH] PCI / PM: Block races between runtime PM and system
 sleep

On Thu, 23 Jun 2011, Rafael J. Wysocki wrote:

> > > Index: linux-2.6/drivers/base/power/runtime.c
> > > ===================================================================
> > > --- linux-2.6.orig/drivers/base/power/runtime.c
> > > +++ linux-2.6/drivers/base/power/runtime.c
> > > @@ -455,12 +455,14 @@ static int rpm_resume(struct device *dev
> > >  	dev_dbg(dev, "%s flags 0x%x\n", __func__, rpmflags);
> > >  
> > >   repeat:
> > > -	if (dev->power.runtime_error)
> > > +	if (dev->power.runtime_error) {
> > >  		retval = -EINVAL;
> > > -	else if (dev->power.disable_depth > 0)
> > > -		retval = -EAGAIN;
> > > -	if (retval)
> > >  		goto out;
> > > +	} else if (dev->power.disable_depth > 0) {
> > > +		if (!(rpmflags & RPM_GET_PUT))
> > > +			retval = -EAGAIN;
> > 
> > Do you also want to check the current status?  If it isn't RPM_ACTIVE 
> > then perhaps you should return an error.
> 
> That depends on whether or not we want RPM_ACTIVE to have any meaning for
> devices whose power.disable_depth is nonzero.  My opinion is that if
> power.disable_depth is nonzero, the runtime PM status of the device
> shouldn't matter (it may be changed on the fly in ways that need not
> reflect the real status).

Then maybe this disable_depth > 0 case should return something other
than 0.  Something new, like -EACCES.  That way the caller would
realize something strange was going on but wouldn't have to treat the 
situation as an error.

After all, the return value from pm_runtime_get_sync() is documented to 
be the error code for the underlying pm_runtime_resume().  It doesn't 
refer to the increment operation -- that always succeeds.

Alan Stern

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