Re: [broken-out-2007-07-20-00-22] kernel bug at kernel/params:570

Satyam Sharma
2007-07-21T03:21:48Z

[ Considering this has sufficiently excited me, I became the second person
to illegitimately download 2.6.22-mm1 and am presently building Michal's
config. The strange thing is that I couldn't get 22-mm1 to even build with
the posted .config -- so had to deselect XFS, ATA, unionfs.

Hopefully this bug should be 100% reproducible at boot time anyway.
Don't care much for XFS and unionfs, but hoping deselecting ATA from
the config doesn't change the variables much in this equation. ]

On 7/21/07, Greg KH <gregkh@suse.de> wrote:
> On Fri, Jul 20, 2007 at 06:37:33PM -0700, Andrew Morton wrote:
> > On Fri, 20 Jul 2007 18:02:57 -0700 Greg KH <gregkh@suse.de> wrote:
> >
> > > --- a/kernel/params.c
> > > +++ b/kernel/params.c
> > > @@ -567,7 +567,11 @@ static void __init kernel_param_sysfs_se
> > > kobject_set_name(&mk->kobj, name);
> > > kobject_init(&mk->kobj);
> > > ret = kobject_add(&mk->kobj);
> > > - BUG_ON(ret < 0);
> > > + if (ret) {
> > > + printk(KERN_ERR "module '%s' failed to be added to sysfs, "
> > > + "the system will be unstable now.\n", name);
> > > + return;
> > > + }
> >
> > It would be nice to print the value of `ret' too.

What I'm surprised about is that %eax doesn't seem to contain the
return value `ret' of kobject_add(). It's 1, which is funny, given:

ret = kobject_add(&mk->kobj);
BUG_ON(ret < 0);

One wouldn't expect BUG() -- or the corresponding exception handler --
to clobber registers, that would be a sad day.

> Ok, how about this version:
>
> ---
> kernel/params.c | 7 ++++++-
> 1 file changed, 6 insertions(+), 1 deletion(-)
>
> --- a/kernel/params.c
> +++ b/kernel/params.c
> @@ -567,7 +567,12 @@ static void __init kernel_param_sysfs_se
> kobject_set_name(&mk->kobj, name);
> kobject_init(&mk->kobj);
> ret = kobject_add(&mk->kobj);
> - BUG_ON(ret < 0);
> + if (ret) {
> + printk(KERN_ERR "Module '%s' failed to be added to sysfs, "
> + "error number %d\n", name, ret);
> + printk(KERN_ERR "The system will be unstable now.\n");
> + return;
> + }
> param_sysfs_setup(mk, kparam, num_params, name_skip);
> kobject_uevent(&mk->kobj, KOBJ_ADD);
> }

I'm building with this:

if (ret) {
printk("~~~~~ .%s.%d.%s. ~~~~~\n", name, ret, kparam->name);
return;
}

To also print out the evil kparam->name that caused us to crash.
When ret == EINVAL, name would be "", so not so helpful alone.

Also enabling netconsole, though I'm sure there's zero chances
of NET / ethXXX / netconsole being up _this_ early in the boot ...

Will keep you guys posted :-)

Satyam