| Message ID | 201104230011.48073.rjw@sisk.pl (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Monday, April 25, 2011, Rafael J. Wysocki wrote: > 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. Well, there haven't been any objections, so I'm adding the patch below to my linux-next branch. Thanks, Rafael > --- > From: Rafael J. Wysocki <rjw@sisk.pl> > 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 <rjw@sisk.pl> > --- > 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-mmc" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
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); + 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); } }