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

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

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
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/