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

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Message-ID: <CACVXFVNyRYzk1Le+QaJr-nnbDCsGqWtx-VJ5X-K6np1+gLzRpA@mail.gmail.com>
Date:	Fri, 12 Apr 2013 17:42:46 +0800
From:	Ming Lei <tom.leiming@...il.com>
To:	Oliver Neukum <oliver@...kum.org>
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 Fri, Apr 12, 2013 at 2:37 PM, Oliver Neukum <oliver@...kum.org> wrote:
>> 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)

OK, got it, it should be both since reset can't move on, so
memory reclaim can't complete to satisfy the allocation.

But I am wondering if it is a case which is worth the consideration.

Almost all USB probe() allocate memory with GFP_KERNEL, then
the similar scenario(data loss only this time) might happen too. Do we
need to fix all USB drivers?

Wrt. the usbnet_status_start() API, looks no good reason to call
it in another queue context, it should be enough to call it in probe() or
bind() if init_status() can be put before info->bind() in usbnet_probe().

Then looks the mem_flags isn't needed in both cases, and we should
always take GFP_NOIO inside the API?

Thanks,
-- 
Ming Lei
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