linux-kernel - Re: WARNING: at lib/debugobjects.c:262 debug_print

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Date:	Wed, 25 Jan 2012 15:05:03 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Jeff Layton <jlayton@...hat.com>
cc:	Boaz Harrosh <bharrosh@...asas.com>,
	Stanislaw Gruszka <sgruszka@...hat.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	linux-kernel@...r.kernel.org, bfields@...hat.com,
	linux-nfs@...r.kernel.org, Tejun Heo <tj@...nel.org>
Subject: Re: WARNING: at lib/debugobjects.c:262
 debug_print_object+0x8c/0xb0()

On Tue, 24 Jan 2012, Jeff Layton wrote:
> > Still, I wonder if there are other problems like this around. The slab
> > allocators seem to call debug_check_no_obj_freed() on kmem_cache_free,
> > but parts of the objects themselves (like the timer in the work object
> > here) get initialized in other places and aren't necessarily
> > reinitialized when they're recycled out of the slab...
> > 
> 
> On second thought...getting rid of the ctor function here might be
> problematic. We have to call inode_init_once, etc...
> 
> Almost all of the inode slabs have one, so I've settled for just moving
> the INIT_DELAYED_WORK call out of init_once and into rpc_alloc_inode. I
> sent a patch to Trond and linux-nfs to do that. That will fix this
> case, but I do wonder if there are other places in the kernel that have
> similar problems with debugobject initialization.

The problem is that debugobject requires that a newly allocated object
is reinitialized and made available to the debugobjects code again
simply because we remove it from the debugobjects core on
kmem_cache_free(). 

The real question is why the heck kmem_cache_alloc() does not call the
ctor on each allocation and just expects the previously used and freed
object to be in a consistent initialiazed state.

Thanks,

	tglx
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