Re: port-xen/47057: Xen NetBSD DomU file system trash under Linux Dom0

[Manuel Bouyer <bouyer%antioche.eu.org@localhost>]

The following reply was made to PR port-xen/47057; it has been noted by GNATS.

From: Manuel Bouyer <bouyer%antioche.eu.org@localhost>
To: Roger Pau =?iso-8859-1?Q?Monn=E9?= <roger.pau%citrix.com@localhost>
Cc: "gnats-bugs%NetBSD.org@localhost" <gnats-bugs%NetBSD.org@localhost>,
        "port-xen-maintainer%netbsd.org@localhost" 
<port-xen-maintainer%NetBSD.org@localhost>,
        "gnats-admin%netbsd.org@localhost" <gnats-admin%NetBSD.org@localhost>,
        "netbsd-bugs%netbsd.org@localhost" <netbsd-bugs%NetBSD.org@localhost>,
        "royger%netbsd.org@localhost" <royger%NetBSD.org@localhost>
Subject: Re: port-xen/47057: Xen NetBSD DomU file system trash under Linux
 Dom0
Date: Sat, 20 Oct 2012 17:57:21 +0200

 On Sat, Oct 20, 2012 at 05:48:08PM +0200, Roger Pau Monné wrote:
 > > 
 > >> Will compile a new kernel with -g and let's see
 > >> what I can get, but I bet xenbus_thread is blocked at:
 > >>
 > >> 831: printk("XENBUS error %d while reading message\n", err);
 > >>
 > >> In fact I'm going to replace that with a panic.
 > > 
 > > Maybe just a printf instead of a printk at first.
 > 
 > Tried that in the past (replacing the printk with a printf), and then I
 > just get in an infite printf loop, intf->rsp_cons and intf->rsp_prod are
 > corrupted, check_indexes in xb_read always returns false and this leads
 > to a infinite loop in xenbus_thread because process_msg always return error.
 > 
 > I've now compiled a kernel that has the panic and prints the ring
 > indexes. What's the best way to check who modifies intf->rsp_cons and
 > intf->rsp_prod? Will ddb watch work on this kind of memory region?
 
 You can try, but at first glance I'd say it won't work. 
 
 Can you determine if it's cons or prod (or both) which is corrupted,
 and in which way ? What are the values when it's corrupted ?
 Are they always the same ?
 
 -- 
 Manuel Bouyer <bouyer%antioche.eu.org@localhost>
      NetBSD: 26 ans d'experience feront toujours la difference
 --