linux-kernel - Re: [PATCH 1/2] usbip: Remove repeated setting of hcd->state in vhci_bus

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Date:   Tue, 14 May 2019 20:58:23 +0900
From:   Suwan Kim <suwan.kim027@...il.com>
To:     shuah <shuah@...nel.org>
Cc:     valentina.manea.m@...il.com, gregkh@...uxfoundation.org,
        linux-usb@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] usbip: Remove repeated setting of hcd->state in
 vhci_bus_suspend()

On Wed, May 08, 2019 at 11:28:05AM -0600, shuah wrote:
> On 5/7/19 9:49 AM, Suwan Kim wrote:
> > Hi Shuah,
> > 
> > On Mon, May 06, 2019 at 09:13:02AM -0600, shuah wrote:
> > > On 5/6/19 6:55 AM, Suwan Kim wrote:
> > > > When hcd suspends execution, hcd_bus_suspend() calls vhci_bus_suspend()
> > > > which sets hcd->state as HC_STATE_SUSPENDED. But after calling
> > > > vhci_bus_suspend(), hcd_bus_suspend() also sets hcd->state as
> > > > HC_STATE_SUSPENDED.
> > > > So, setting hcd->state in vhci_hcd_suspend() is unnecessary.
> > > > 
> > > > Signed-off-by: Suwan Kim <suwan.kim027@...il.com>
> > > > ---
> > > >    drivers/usb/usbip/vhci_hcd.c | 4 ----
> > > >    1 file changed, 4 deletions(-)
> > > > 
> > > > diff --git a/drivers/usb/usbip/vhci_hcd.c b/drivers/usb/usbip/vhci_hcd.c
> > > > index 667d9c0ec905..e6f378d00fb6 100644
> > > > --- a/drivers/usb/usbip/vhci_hcd.c
> > > > +++ b/drivers/usb/usbip/vhci_hcd.c
> > > > @@ -1238,10 +1238,6 @@ static int vhci_bus_suspend(struct usb_hcd *hcd)
> > > >    	dev_dbg(&hcd->self.root_hub->dev, "%s\n", __func__);
> > > > -	spin_lock_irqsave(&vhci->lock, flags);
> > > > -	hcd->state = HC_STATE_SUSPENDED;
> > > > -	spin_unlock_irqrestore(&vhci->lock, flags);
> > > > -
> > > >    	return 0;
> > > >    }
> > > > 
> > > 
> > > Tell me more about why you think this change is needed? How did you test
> > > this change?
> > 
> > I think that host controller specific functions, vhci_bus_resume()
> > or vhci_bus_suspend() in the case of vhci, usually process host
> > controller specific data (struct vhci_hcd) not a generic data
> > (struct usb_hcd). The generic data is usually processed by generic HCD
> > layer. But vhci_bus_resume() and vhci_bus_suspend() set generic data
> > (hcd->state) and moreover this variable is set in generic HCD layer
> > once again(hcd_bus_resume() and hcd_bus_suspend()).
> > 
> > So, i think host controller specific functions (vhci_bus_resume()
> > and vhci_bus_suspend()) don't need to set the generic data that is
> > "hcd->state = HC_STATE_RUNNING or HC_STATE_SUSPEND".
> > 
> 
> It depends. In this case, vhci_hcd is virtual driver and maintains
> port status for devices that are remote. It checks hcd->state in
> vhci_hub_status().
> 
> It updates the hcd->state in suspend with vhci->lock hold and checks
> status from vhci_hub_status(). Removing updating hcd->state from
> vhci_bus_suspend()will open a window where vhci_hub_status() might
> find it wrong state.
> 

I didn't know that and I missed. Thank you for pointing out my fault.
I agree that removing updating hcd->state which is protected by vhci
lock is not correct.

But I still have not fully understood the relationship between
vhci_bus_suspend() and vhci_hub_status() yet. I will look at it in
more detail. Again, thank you for reviewing my patch.

Regards

Suwan Kim