netdev - Re: [PATCH] usbnet: runtime pm: fix out of memory

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Date:	Tue, 3 May 2011 09:53:44 +0200
From:	Oliver Neukum <oneukum@...e.de>
To:	David Miller <davem@...emloft.net>
Cc:	tom.leiming@...il.com, netdev@...r.kernel.org,
	linux-usb@...r.kernel.org
Subject: Re: [PATCH] usbnet: runtime pm: fix out of memory

Am Dienstag, 3. Mai 2011, 00:52:14 schrieb David Miller:
> From: tom.leiming@...il.com
> Date: Fri, 29 Apr 2011 16:37:09 +0800
> 
> > From: Ming Lei <tom.leiming@...il.com>
> > 
> > This patch makes use of the EVENT_DEV_OPEN flag introduced recently to
> > fix one out of memory issue, which can be reproduced on omap3/4 based
> > pandaboard/beagle XM easily with steps below:
>  ...
> 
> Oliver please review this patch.  Thanks!
> 
> >       - enable runtime pm
> >       echo auto > /sys/devices/platform/usbhs-omap.0/ehci-omap.0/usb1/1-1/1-1.1/power/control
> > 
> >       - ifconfig eth0 up
> > 
> >       - then out of memroy happened, see [1] for kernel message.
> > 
> > Follows my analysis:
> >       - 'ifconfig eth0 up' brings eth0 out of suspend, and usbnet_resume
> >       is called to schedule dev->bh, then rx urbs are submited to prepare for
> >       recieving data;
> > 
> >       - some usbnet devices will produce garbage rx packets flood if
> >       info->reset is not called in usbnet_open.
> > 
> >       - so there is no enough chances for usbnet_bh to handle and release
> >       recieved skb buffers since many rx interrupts consumes cpu, so out of memory
> >       for atomic allocation in rx_submit happened.
> > 
> > This patch fixes the issue by simply not allowing schedule of usbnet_bh until device
> > is opened.

Do the devices in question use cdc_ether?
The problem I see with this patch is that cdc_ether uses .reset_resume = usbnet_resume
Therefore the device will not have been reset from the viewpoint of the device, yet
the device may be open, so the bug would strike again.

It seems to me that this patch is not wrong as such, but incomplete.

	Regards
		Oliver

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