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

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Message-ID: <CACVXFVPdOkvKBBrshnmQv5cYVdDhi8j0V_WxNwBU9VuDsCLkXA@mail.gmail.com>
Date:	Fri, 12 Oct 2012 09:43:56 +0800
From:	Ming Lei <ming.lei@...onical.com>
To:	Alan Stern <stern@...land.harvard.edu>
Cc:	Oliver Neukum <oneukum@...e.de>,
	"David S. Miller" <davem@...emloft.net>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	netdev@...r.kernel.org, linux-usb@...r.kernel.org
Subject: Re: [PATCH 01/12] usbnet: introduce usbnet 3 command helpers

On Thu, Oct 11, 2012 at 10:36 PM, Alan Stern <stern@...land.harvard.edu> wrote:

>
> It's worse than you may realize.  When a SCSI disk is suspended, all of
> its ancestor devices may be suspended too.  Pages can't be read in from
> the drive until all those ancestors are resumed.  This means that all
> runtime resume code paths for all drivers that could be bound to an
> ancestor of a block device must avoid GFP_KERNEL.  In practice it's

Exactly, so several subsystems(for example, pci, usb, scsi) will be involved,
and converting GFP_KERNEL in runtime PM path to GFP_NOIO becomes
more difficult.

> probably easiest for the runtime PM core to use tsk_set_allowd_gfp()
> before calling any runtime_resume method.

Yes, it might be done in usb runtime resume context because all
usb device might include a mass storage interface. But, in fact,
we can find if there is one mass storage interface on the current
configuration easily inside usb_runtime_resume().

Also, we can loose the constraint in runtime PM core, before calling
runtime_resume callback for one device, the current context is marked
as ~GFP_IOFS only if it is a block device or there is one block device
descendant. But the approach becomes a bit complicated because
device tree traversing is involved.

Thanks,
--
Ming Lei
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