linux-kernel - Re: [PATCH] lib/idr.c: Zero memory properly in idr_remove

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Message-Id: <20090114012234.bce79d7b.akpm@linux-foundation.org>
Date:	Wed, 14 Jan 2009 01:22:34 -0800
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Stefan Richter <stefanr@...6.in-berlin.de>
Cc:	Pekka Enberg <penberg@...helsinki.fi>,
	Manfred Spraul <manfred@...orfullife.com>, krh@...hat.com,
	dcm@....org, Nadia.Derbey@...l.net,
	linux1394-devel@...ts.sourceforge.net,
	linux-kernel@...r.kernel.org, paulmck@...ibm.com, stable@...nel.org
Subject: Re: [PATCH] lib/idr.c: Zero memory properly in idr_remove_all

On Wed, 14 Jan 2009 09:59:07 +0100 Stefan Richter <stefanr@...6.in-berlin.de> wrote:

> > --- a/lib/idr.c~lib-idrc-use-kmem_cache_zalloc-for-the-idr_layer-cache
> > +++ a/lib/idr.c
> > @@ -121,7 +121,7 @@ int idr_pre_get(struct idr *idp, gfp_t g
> >  {
> >  	while (idp->id_free_cnt < IDR_FREE_MAX) {
> >  		struct idr_layer *new;
> > -		new = kmem_cache_alloc(idr_layer_cache, gfp_mask);
> > +		new = kmem_cache_zalloc(idr_layer_cache, gfp_mask);
> >  		if (new == NULL)
> >  			return (0);
> >  		move_to_free_list(idp, new);
> ...
> 
> I wonder if it would be more robust --- or even necessary --- to instead
> add proper initialization code to get_from_free_list().
> 
> As far as David and I tested the new idr using code in firewire, we
> called idr_remove_all() *and* idr_destroy() before any subsequent
> idr_get_new().  But in practice, idr_get_new() may of course also happen
> between idr_remove_all() and idr_destroy().
> 
> And then this fix won't be sufficient, would it?

Maybe I'm having a thick day, but I'm not following you at all here.

What do you think the remaining problem is?  get_from_free_list()
starts out with a not-fully-zeroed object?  Something else?

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