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

Satyam Sharma
2007-07-20T23:43:21Z

On 7/21/07, Greg KH <gregkh@suse.de> wrote:
> On Fri, Jul 20, 2007 at 03:59:12PM -0700, Andrew Morton wrote:
> > On Fri, 20 Jul 2007 15:50:47 -0700
> > Greg KH <gregkh@suse.de> wrote:
> >
> > > On Fri, Jul 20, 2007 at 06:32:21PM +0200, Michal Piotrowski wrote:
> > > > Hi Greg,
> > > >
> > > > This looks like a sysfs bug
> > > > http://www.stardust.webpages.pl/files/tbf/bitis-gabonica/
> > > > broken-out-2007-07-20-00-22/00003.jpg
> > > >
> > > > l *kernel_param_sysfs_setup+0x75
> > > > 0xc13c0894 is in kernel_param_sysfs_setup (kernel/params.c:570).
> > > > 565 mk->mod = THIS_MODULE;
> > > > 566 kobj_set_kset_s(mk, module_subsys);
> > > > 567 kobject_set_name(&mk->kobj, name);
> > > > 568 kobject_init(&mk->kobj);
> > > > 569 ret = kobject_add(&mk->kobj);
> > > > 570 BUG_ON(ret < 0);
> > > > 571 param_sysfs_setup(mk, kparam, num_params, name_skip);
> > > > 572 kobject_uevent(&mk->kobj, KOBJ_ADD);
> > > > 573 }
> > > > 574
> > > >
> > > > http://www.stardust.webpages.pl/files/tbf/bitis-gabonica/broken-out-2007-07-20-00-22/mm-config
> > >
> > > What kernel version is this happening on? The -mm tree? Can you try
> > > Linus's tree instead?
> > >
> > > It looks like there was some needed information right before the first
> > > stack dump, showing exactly what kobject was trying to be added that was
> > > already present. Odds are this is a kernel parameter with the same name
> > > as a duplicate one within the same module,

I don't think that's an -EEXIST.

I think what we have here is kobject_add() exiting with -EINVAL.
(kobject attempted to be registered with no name!)

[ The first trace on that screen shows: kobject_shadow_add+0x5b/0x189.
That's the WARN_ON(1) at lib/kobject.c:176. If it was a EEXIST case,
we would've seen an offset in kobject_shadow_add closer to 0x189,
because the dump_stack() for EEXIST is barely 4 instructions before
we return from that function. ]

> > > but the trick is going to be
> > > trying to figure out what module is causing this.

So I'd guess we want to search for a module that's passing a kobject *
to kobject_add() such that !kobj->k_name is true.

> > > So it's not a sysfs bug, but rather a driver issue that this is
> > > catching.
> >
> > In that case a BUG was way too harsh treatment, and in fact directly
> > contributed to our inability to debug the bug!
> >
> > Can we wind that back a bit? Add some useful printks and then recover
> > in some fashion?
> [...]
> So I'm guessing he was trying to catch something specific here.

Considering that:

(1) This isn't a bug that should bring down the kernel that hard, and,
(2) kobject_shadow_add() seems to be dumping enough stacks and
printing printk's on errors already,

I'd suggest to just get rid of the BUG_ON() in kernel_param_sysfs_setup()

Satyam