Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758273Ab1DYK3M (ORCPT ); Mon, 25 Apr 2011 06:29:12 -0400 Received: from ogre.sisk.pl ([217.79.144.158]:47985 "EHLO ogre.sisk.pl" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758208Ab1DYK3K (ORCPT ); Mon, 25 Apr 2011 06:29:10 -0400 From: "Rafael J. Wysocki" To: linux-pm@lists.linux-foundation.org Subject: Re: [linux-pm] [PATCH/RFC] MMC: remove unbalanced pm_runtime_suspend() Date: Mon, 25 Apr 2011 12:29:27 +0200 User-Agent: KMail/1.13.6 (Linux/2.6.39-rc4+; KDE/4.6.0; x86_64; ; ) Cc: Alan Stern , linux-mmc@vger.kernel.org, Magnus Damm , Guennadi Liakhovetski , LKML References: <201104230011.48073.rjw@sisk.pl> In-Reply-To: <201104230011.48073.rjw@sisk.pl> MIME-Version: 1.0 Content-Type: Text/Plain; charset="iso-8859-1" Content-Transfer-Encoding: 7bit Message-Id: <201104251229.27263.rjw@sisk.pl> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 5781 Lines: 141 On Saturday, April 23, 2011, Rafael J. Wysocki wrote: > On Friday, April 22, 2011, Alan Stern wrote: > > On Fri, 22 Apr 2011, Rafael J. Wysocki wrote: > > > > > > The barrier would not prevent the race between the notifier and runtie PM > > > > from taking place. Why don't we do something like this instead: > > > > > > > > --- > > > > drivers/base/dd.c | 3 ++- > > > > 1 file changed, 2 insertions(+), 1 deletion(-) > > > > > > > > Index: linux-2.6/drivers/base/dd.c > > > > =================================================================== > > > > --- linux-2.6.orig/drivers/base/dd.c > > > > +++ linux-2.6/drivers/base/dd.c > > > > @@ -326,6 +326,8 @@ static void __device_release_driver(stru > > > > BUS_NOTIFY_UNBIND_DRIVER, > > > > dev); > > > > > > > > + pm_runtime_put_sync(dev); > > > > + > > > > > > In fact, I think this one may be _noidle. If we allow the bus/driver > > > to do what they wont, we might as well let them handle the "device idle" > > > case from ->remove(). > > > > Maybe... But keeping it put_sync doesn't do any harm. In Guennadi's > > case, it might allow him to get rid of the pm_runtime_suspend() call in > > the remove routine. > > > > > > if (dev->bus && dev->bus->remove) > > > > dev->bus->remove(dev); > > > > else if (drv->remove) > > > > @@ -338,7 +340,6 @@ static void __device_release_driver(stru > > > > BUS_NOTIFY_UNBOUND_DRIVER, > > > > dev); > > > > > > > > - pm_runtime_put_sync(dev); > > > > } > > > > } > > > > Basically this is okay with me, and it should allow Guennadi to avoid > > the extra put/get pair. > > OK, so I'm going to put the appended patch into my linux-next branch > (hopefully, the problem is explained sufficiently in the changelog). I thought about that a bit more and came to the conclusion that we should do things a bit differently in __device_release_driver(). Namely, the fact that the device can be resumed (either synchronously or asynchronously) after the pm_runtime_barrier() has returned may be problematic too, because it may race with the bus notifier in some cases. For this reason, I think it would be better to do pm_runtime_get_sync() instead of the pm_runtime_get_noresume() and pm_runtime_barrier(). So, I think the appended patch would be better than the previous one. Thanks, Rafael --- From: Rafael J. Wysocki Subject: PM / Runtime: Rework runtime PM handling during driver removal The driver core tries to prevent race conditions between runtime PM and driver removal from happening by incrementing the runtime PM usage counter of the device and executing pm_runtime_barrier() before running the bus notifier and the ->remove() callbacks provided by the device's subsystem or driver. This guarantees that, if a future runtime suspend of the device has been scheduled or a runtime resume or idle request has been queued up right before the driver removal, it will be canceled or waited for to complete and no other asynchronous runtime suspend or idle requests for the device will be put into the PM workqueue until the ->remove() callback returns. However, it doesn't prevent resume requests from being queued up after pm_runtime_barrier() has been called and it doesn't prevent pm_runtime_resume() from executing the device subsystem's runtime resume callback. Morever, it prevents the device's subsystem or driver from putting the device into the suspended state by calling pm_runtime_suspend() from its ->remove() routine. This turns out to be a major inconvenience for some subsystems and drivers that want to leave the devices they handle in the suspended state. To really prevent runtime PM callbacks from racing with the bus notifier callback in __device_release_driver(), which is necessary, because the notifier is used by some subsystems to carry out operations affecting the runtime PM functionality, use pm_runtime_get_sync() instead of the combination of pm_runtime_get_noresume() and pm_runtime_barrier(). This will resume the device if it's in the suspended state and will prevent it from being suspended again until pm_runtime_put_*() is called. To allow subsystems and drivers to put devices into the suspended state by calling pm_runtime_suspend() from their ->remove() routines, execute pm_runtime_put_sync() after running the bus notifier in __device_release_driver(). This will require subsystems and drivers to make their ->remove() callbacks avoid races with runtime PM directly, but it will allow of more flexibility in the handling of devices during the removal of their drivers. Signed-off-by: Rafael J. Wysocki --- drivers/base/dd.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) Index: linux-2.6/drivers/base/dd.c =================================================================== --- linux-2.6.orig/drivers/base/dd.c +++ linux-2.6/drivers/base/dd.c @@ -316,8 +316,7 @@ static void __device_release_driver(stru drv = dev->driver; if (drv) { - pm_runtime_get_noresume(dev); - pm_runtime_barrier(dev); + pm_runtime_get_sync(dev); driver_sysfs_remove(dev); @@ -326,6 +325,8 @@ static void __device_release_driver(stru BUS_NOTIFY_UNBIND_DRIVER, dev); + pm_runtime_put_sync(dev); + if (dev->bus && dev->bus->remove) dev->bus->remove(dev); else if (drv->remove) @@ -338,7 +339,6 @@ static void __device_release_driver(stru BUS_NOTIFY_UNBOUND_DRIVER, dev); - pm_runtime_put_sync(dev); } } -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/