netdev - Re: [PATCH 1/2 v5] usbnet: allow status interrupt URB to always be active

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Date:	Fri, 12 Apr 2013 08:37:24 +0200
From:	Oliver Neukum <oliver@...kum.org>
To:	Ming Lei <tom.leiming@...il.com>
Cc:	Dan Williams <dcbw@...hat.com>,
	Elina Pasheva <epasheva@...rrawireless.com>,
	Network Development <netdev@...r.kernel.org>,
	linux-usb <linux-usb@...r.kernel.org>,
	Rory Filer <rfiler@...rrawireless.com>,
	Phil Sutter <phil@....cc>
Subject: Re: [PATCH 1/2 v5] usbnet: allow status interrupt URB to always be active

On Thursday 11 April 2013 20:59:05 Ming Lei wrote:
> On Thu, Apr 11, 2013 at 8:28 PM, Oliver Neukum <oliver@...kum.org> wrote:
> > On Thursday 11 April 2013 20:11:13 Ming Lei wrote:
> >> On Thu, Apr 11, 2013 at 7:14 PM, Oliver Neukum <oliver@...kum.org> wrote:
> >> >
> >> > Sorry, I misunderstood.
> >>
> >> No problem, :-)
> >>
> >> >
> >> > Task A                                  Task B                          queue
> >> >
> >> > queue work
> >> >                                                 request a reset
> >> >                                                                                         allocate memory and block
> >> >                                                 cancel the work
> >> >                                                                                         shit happened
> >>
> >> If I understand the case correctly, the above deadlock can be avoided
> >> by canceling rx/tx URBs at the end of pre_reset() or usbnet_disconnect(),
> >
> > No. cancel_work_sync() must wait for the work. The work will not finish.
> 
> The work will complete when memory is reclaimed, and the rx/tx path is
> still working, so memory reclaim can continue and the deadlock may not
> be caused, may it?

Only if the memory allocation goes to the same interface. If the blocking interface
is storage, something bad happens (data loss not deadlock)

	Regards
		Oliver

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