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

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Date:	Sat, 21 Jul 2007 05:13:12 +0530
From:	"Satyam Sharma" <satyam.sharma@...il.com>
To:	"Greg KH" <gregkh@...e.de>
Cc:	"Andrew Morton" <akpm@...ux-foundation.org>, rdunlap@...otime.net,
	"Michal Piotrowski" <michal.k.k.piotrowski@...il.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [broken-out-2007-07-20-00-22] kernel bug at kernel/params:570

On 7/21/07, Greg KH <gregkh@...e.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@...e.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
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