linux-kernel - Re: Subject: [PATCH] drivers-core: move device_pm_remove behind bus_remove

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Date:	Mon, 15 Oct 2012 15:39:49 +0800
From:	Yanmin Zhang <yanmin_zhang@...ux.intel.com>
To:	"Zhang, LongX" <longx.zhang@...el.com>,
	Alan Stern <stern@...land.harvard.edu>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pm@...ts.linux-foundation.org" 
	<linux-pm@...ts.linux-foundation.org>, "rjw@...k.pl" <rjw@...k.pl>
Subject: Re: Subject: [PATCH] drivers-core: move device_pm_remove behind
 bus_remove_device

On Fri, 2012-09-21 at 01:58 +0000, Zhang, LongX wrote:
> From: LongX Zhang <longx.zhang@...el.com>
> 
> 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 ingored. 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.
The background about the patch: We hit an hang issue when removing a mmc
device on Medfield Android phone by sysfs interface.

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>
> ---
>  drivers/base/core.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/base/core.c b/drivers/base/core.c
> index 5e6e00b..81ea7f2 100644
> --- a/drivers/base/core.c
> +++ b/drivers/base/core.c
> @@ -1169,7 +1169,6 @@ void device_del(struct device *dev)
>  	if (dev->bus)
>  		blocking_notifier_call_chain(&dev->bus->p->bus_notifier,
>  					     BUS_NOTIFY_DEL_DEVICE, dev);
> -	device_pm_remove(dev);
>  	dpm_sysfs_remove(dev);
>  	if (parent)
>  		klist_del(&dev->p->knode_parent);
> @@ -1194,6 +1193,7 @@ void device_del(struct device *dev)
>  	device_remove_file(dev, &uevent_attr);
>  	device_remove_attrs(dev);
>  	bus_remove_device(dev);
> +	device_pm_remove(dev);
>  	driver_deferred_probe_del(dev);
>  
>  	/*


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