netdev - Re: [PATCH 01/12] usbnet: introduce usbnet 3 command helpers

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Message-ID: <1588459.VLxBbnNMlP@linux-lqwf.site>
Date:	Thu, 11 Oct 2012 06:11:58 +0200
From:	Oliver Neukum <oneukum@...e.de>
To:	Ming Lei <ming.lei@...onical.com>
Cc:	"David S. Miller" <davem@...emloft.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	netdev@...r.kernel.org, linux-usb@...r.kernel.org,
	Alan Stern <stern@...land.harvard.edu>
Subject: Re: [PATCH 01/12] usbnet: introduce usbnet 3 command helpers

On Thursday 11 October 2012 11:18:22 Ming Lei wrote:
> On Wed, Oct 10, 2012 at 1:51 PM, Oliver Neukum <oneukum@...e.de> wrote:
> >
> > No, the problem is autoresume.
> >
> > Suppose we have a device with two interface. Interface A be usbnet; interface B
> > something you page on. Now consider that you can only resume both interfaces
> > and this is (and needs to be) done synchronously.
> >
> > Now we can have this code path:
> >
> > autoresume of device -> resume() -> kmalloc(..., GFP_KERNEL) ->
> > VM layer decides to start paging out -> IO to interface B -> autoresume of device
> > --> DEADLOCK
> 
> Currently scsi disk can only be runtime suspended when the device is not
> opened, so are you sure that the paging out above can cause IO on a suspend
> usb mass storage disk which is not mounted or opened by utility now?

We definitely do not wish to keep it that way. People at Intel are currently working
on better power management for sd, which would allow full autosuspend.

	Regards
		Oliver

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