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

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Message-ID: <CACVXFVMynoPm6_wYj2MD-5SvMpB7e1Wk94=XMp588rD8hU=eew@mail.gmail.com>
Date:	Thu, 11 Oct 2012 11:18:22 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Oliver Neukum <oneukum@...e.de>
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 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?


Thanks,
--
Ming Lei
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