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

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Date:	Thu, 23 Jun 2011 22:49:34 +0200
From:	"Rafael J. Wysocki" <rjw@...k.pl>
To:	Alan Stern <stern@...land.harvard.edu>
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 Thursday, June 23, 2011, Alan Stern wrote:
> On Thu, 23 Jun 2011, Rafael J. Wysocki wrote:
> 
> > OK, so what about the appended patch (the last hunk is necessary to make the
> > SCSI error handling work when runtime PM is disabled, it should be a separate
> > patch)?
> > 
> > Rafael
> > 
> > ---
> >  drivers/base/power/main.c    |   27 ++++++++++++++++++++++-----
> >  drivers/base/power/runtime.c |   10 ++++++----
> >  2 files changed, 28 insertions(+), 9 deletions(-)
> > 
> > Index: linux-2.6/drivers/base/power/main.c
> > ===================================================================
> > --- linux-2.6.orig/drivers/base/power/main.c
> > +++ linux-2.6/drivers/base/power/main.c
> > @@ -505,6 +505,7 @@ static int legacy_resume(struct device *
> >  static int device_resume(struct device *dev, pm_message_t state, bool async)
> >  {
> >  	int error = 0;
> > +	bool put = false;
> >  
> >  	TRACE_DEVICE(dev);
> >  	TRACE_RESUME(0);
> > @@ -521,6 +522,9 @@ static int device_resume(struct device *
> >  	if (!dev->power.is_suspended)
> >  		goto Unlock;
> >  
> > +	pm_runtime_enable(dev);
> > +	put = true;
> > +
> >  	if (dev->pwr_domain) {
> >  		pm_dev_dbg(dev, state, "power domain ");
> >  		error = pm_op(dev, &dev->pwr_domain->ops, state);
> > @@ -563,6 +567,10 @@ static int device_resume(struct device *
> >  	complete_all(&dev->power.completion);
> >  
> >  	TRACE_RESUME(error);
> > +
> > +	if (put)
> > +		pm_runtime_put_sync(dev);
> > +
> >  	return error;
> >  }
> >  
> > @@ -843,16 +851,22 @@ static int __device_suspend(struct devic
> >  	int error = 0;
> >  
> >  	dpm_wait_for_children(dev, async);
> > -	device_lock(dev);
> >  
> >  	if (async_error)
> > -		goto Unlock;
> > +		return 0;
> > +
> > +	pm_runtime_get_noresume(dev);
> > +	if (pm_runtime_barrier(dev) && device_may_wakeup(dev))
> > +		pm_wakeup_event(dev, 0);
> >  
> >  	if (pm_wakeup_pending()) {
> > +		pm_runtime_put_sync(dev);
> >  		async_error = -EBUSY;
> > -		goto Unlock;
> > +		return 0;
> >  	}
> >  
> > +	device_lock(dev);
> > +
> >  	if (dev->pwr_domain) {
> >  		pm_dev_dbg(dev, state, "power domain ");
> >  		error = pm_op(dev, &dev->pwr_domain->ops, state);
> > @@ -890,12 +904,15 @@ static int __device_suspend(struct devic
> >   End:
> >  	dev->power.is_suspended = !error;
> >  
> > - Unlock:
> >  	device_unlock(dev);
> >  	complete_all(&dev->power.completion);
> >  
> > -	if (error)
> > +	if (error) {
> > +		pm_runtime_put_sync(dev);
> >  		async_error = error;
> > +	} else if (dev->power.is_suspended) {
> > +		__pm_runtime_disable(dev, false);
> > +	}
> >  
> >  	return error;
> >  }
> 
> Looks right.

Great!  I'll prepare a final version with a changelog and documentation
update, then.

> > 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).

Thanks,
Rafael
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