On Wed, Oct 24, 2012 at 09:46:19PM +0200, Rafael J. Wysocki wrote: > On Tuesday 16 of October 2012 23:28:08 zhanglong wrote: > > We hit an hang issue when removing a mmc device on Medfield Android phone by sysfs interface. > > > > device_pm_remove will call pm_runtime_remove which would disable > > runtime PM of the device. After that pm_runtime_get* or > > pm_runtime_put* will be ignored. So if we disable the runtime PM > > before device really be removed, drivers' _remove callback may > > access HW even pm_runtime_get* fails. That is bad. > > > > Consider below call sequence when removing a device: > > device_del => device_pm_remove > > => class_intf->remove_dev(dev, class_intf) => pm_runtime_get_sync/put_sync > > => bus_remove_device => device_release_driver => pm_runtime_get_sync/put_sync > > > > remove_dev might call pm_runtime_get_sync/put_sync. > > Then, generic device_release_driver also calls pm_runtime_get_sync/put_sync. > > Since device_del => device_pm_remove firstly, later _get_sync wouldn't really wake up the device. > > > > I git log -p to find the patch which moves the calling to device_pm_remove ahead. > > It's below patch: > > > > commit 775b64d2b6ca37697de925f70799c710aab5849a > > Author: Rafael J. Wysocki <rjw@xxxxxxx> > > Date: Sat Jan 12 20:40:46 2008 +0100 > > > > PM: Acquire device locks on suspend > > > > This patch reorganizes the way suspend and resume notifications are > > sent to drivers. The major changes are that now the PM core acquires > > every device semaphore before calling the methods, and calls to > > device_add() during suspends will fail, while calls to device_del() > > during suspends will block. > > > > It also provides a way to safely remove a suspended device with the > > help of the PM core, by using the device_pm_schedule_removal() callback > > introduced specifically for this purpose, and updates two drivers (msr > > and cpuid) that need to use it. > > > > > > As device_pm_schedule_removal is deleted by another patch, we need also revert other parts of the patch, > > i.e. move the calling of device_pm_remove after the calling to bus_remove_device. > > > > Signed-off-by: LongX Zhang <longx.zhang@xxxxxxxxx> > > Greg, do you see any potential problems with this patch? No, no objection from me: Acked-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
