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

["Satyam Sharma" <satyam.sharma@gmail.com>]

[ 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
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