Re: [Xen-devel] [PATCH] xencons missing string allocation

[Alex Williamson <alex.williamson@xxxxxx>]

On Fri, 2005-12-09 at 13:37 -0700, Alex Williamson wrote:
> On Fri, 2005-12-09 at 20:54 +0200, Muli Ben-Yehuda wrote:
> > On Fri, Dec 09, 2005 at 11:37:31AM -0700, Alex Williamson wrote:
> > 
> > > 
> > >    I was trying to boot dom0 w/ "xencons=ttyS1 console=ttyS1".  It gives
> > > some weird error messages:
> > > 
> > > Warning: dev (ttyS2) tty->count(2) != #fd's(1) in release_dev
> > > Warning: dev (ttyS2) tty->count(3) != #fd's(1) in tty_open
> > > 
> > > And blows up with a page fault.  The page fault is because we don't
> > > actually allocate a buffer for the tty driver name.
> > 
> > Errr... the patch looks curious. Why does it work when ->name points
> > to the heap but not when it points to the data segment? they should be
> > equivalent and many tty drivers appear to set ->name to the data
> > segment. Is something trying to modify xencons_driver->name later?
> 
>    You're right, I guess a lot of tty/char drivers seem to have the name
> on the heap.  However, it would suggest there's a path where the name is
> referenced outside of the context of that function since it prevents a
> page fault.  I'll keep looking to make sure I'm not just getting lucky.

   Ok, disregard that previous attempt, it was definitely chasing a
false positive.  I'm not sure this one is correct either, but I'll toss
it out in case anyone else is interested in chasing this problem too.  I
believe the problem is that kcons_device() is incorrectly calculating
the index when xc_num != 0 on serial devices.  If I subtract xc_num from
the console index, which should always give me 0, things work perfectly
for all ttyS console values (that I've tested).  I don't know if
something similar needs to be done for tty devices.  Patch attached,
comments/suggestions welcome.  Thanks,

        Alex


Signed-off-by: Alex Williamson <alex.williamson@xxxxxx>
---

diff -r 53cff3f88e45 linux-2.6-xen-sparse/drivers/xen/console/console.c
--- a/linux-2.6-xen-sparse/drivers/xen/console/console.c        Fri Dec  9 
11:05:06 2005
+++ b/linux-2.6-xen-sparse/drivers/xen/console/console.c        Fri Dec  9 
16:34:33 2005
@@ -168,7 +168,7 @@
 
 static struct tty_driver *kcons_device(struct console *c, int *index)
 {
-       *index = c->index;
+       *index = c->index - (xc_mode == XC_SERIAL ? xc_num : 0);
        return xencons_driver;
 }
 



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