linux-kernel - Re: [PATCH v2] drivers-core: move the calling to device_pm_remove behind the calling to bus_remove

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Date:	Wed, 24 Oct 2012 15:13:27 -0700
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	"Rafael J. Wysocki" <rjw@...k.pl>
Cc:	zhanglong <longzhax@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	yanmin_zhang@...ux.intel.com,
	Alan Stern <stern@...land.harvard.edu>,
	"linux-pm@...ts.linux-foundation.org" 
	<linux-pm@...ts.linux-foundation.org>
Subject: Re: [PATCH v2] drivers-core: move the calling to device_pm_remove
 behind the calling to bus_remove_device

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@...k.pl>
> > 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@...el.com>
> 
> Greg, do you see any potential problems with this patch?

No, no objection from me:

Acked-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
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