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Message-ID: <20090506213209.GA18511@kroah.com>
Date: Wed, 6 May 2009 14:32:09 -0700
From: Greg KH <greg@...ah.com>
To: Jason Wessel <jason.wessel@...driver.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
On Wed, May 06, 2009 at 03:51:14PM -0500, Jason Wessel wrote:
> 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.
Good, then you just solved your issue with no nasty host driver hack.
> 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?
No you are not, sorry, USB doesn't work without interrupts in this kind
of mode at all.
> 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.
That's going to be "interesting" to try to accomplish :)
good luck,
greg k-h
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