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

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Message-Id: <20070720163735.3ba69e1e.rdunlap@xenotime.net>
Date:	Fri, 20 Jul 2007 16:37:35 -0700
From:	Randy Dunlap <rdunlap@...otime.net>
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 Fri, 20 Jul 2007 16:10:52 -0700 Greg KH 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, but the trick is going to be
> > > trying to figure out what module is causing this.
> > > 
> > > 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?
> 
> Sure, I don't mind doing that at all.
> 
> Hm, it looks like Randy added this back in September last year with:
> 	commit d8c7649e99e4b081b624aefe1e77caa30b53cb18
> 	Author: Randy Dunlap <rdunlap@...otime.net>
> 	Date:   Fri Sep 29 01:58:55 2006 -0700
> 
> 	    [PATCH] kernel/params: driver layer error checking
> 
> 	    Check driver layer return values in kernel/params.c
> 
> 	    Signed-off-by: Randy Dunlap <rdunlap@...otime.net>
> 	    Signed-off-by: Andrew Morton <akpm@...l.org>
> 	    Signed-off-by: Linus Torvalds <torvalds@...l.org>
> 
> (wow, I love git and the signed-off-tree for things like this, it's
> trivial to find this information out.)
> 
> So I'm guessing he was trying to catch something specific here.
> 
> Randy, any objection to changing that BUG_ON to a printk warning instead
> telling the user exactly what needs to be fixed and that the system is
> now going to be unstable when any module is unloaded?

Of course not (no objection).

I added a BUG_ON() ?  Shame on me.

---
~Randy
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