linux-kernel - Re: [PATCH 5/5] usb_debug: EXPERIMENTAL

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Message-ID: <4A01F842.9080300@windriver.com>
Date:	Wed, 06 May 2009 15:51:14 -0500
From:	Jason Wessel <jason.wessel@...driver.com>
To:	Greg KH <greg@...ah.com>
CC:	Oliver Neukum <oliver@...kum.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Alan Cox <alan@...rguk.ukuu.org.uk>, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] usb_debug: EXPERIMENTAL - poll hcd device to forcewrites

Greg KH wrote:
>> Doing enough printk's such as in register_console() will cause loss
>> because you run out of URBs unless you can force them to complete.
>>     
>
> Why not just make the upper bound of urbs very large?  We used to have
> an unlimited number of in-flight urbs for some drivers until it was
> pointed out that a simple:
> 	cat /dev/null > /dev/ttyUSB0
> would cause a DoS :)
>
> What happens if your upper bound is 400?  4000?  Will that work
> properly?
>   
Sure, if you have enough of a urb available, ultimately you get all the
printk's.

If I want to printk from the nmi_watchdog out to this device, am I going
to get anything if the write is not synchronous, because in theory the
hcd device is never going to get accessed again?

Ideally I want to make sure that somehow I get my debug output out to
the console, even if it means we do some polling after the oops state is
set.

Jason.
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