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

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Date:	Mon, 12 Jan 2009 20:53:43 +0100
From:	Manfred Spraul <manfred@...orfullife.com>
To:	Kristian Høgsberg <krh@...hat.com>
CC:	Stefan Richter <stefanr@...6.in-berlin.de>,
	Andrew Morton <akpm@...ux-foundation.org>, dcm@....org,
	Nadia Derbey <Nadia.Derbey@...l.net>,
	linux1394-devel <linux1394-devel@...ts.sourceforge.net>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	"Paul E. McKenney" <paulmck@...ibm.com>
Subject: Re: [PATCH] lib/idr.c: Zero memory properly in idr_remove_all

Kristian Høgsberg wrote:
>   The problem
> isn't about returning un-zeroed-out objects to the kmem cache, the
> problem is returning them to the idr free list.
>   
I think this is wrong:
The slab allocator assumes that the objects that are given to 
kmem_cache_free() are properly constructed.
I.e.: No additional constructor is called prior to returning the object 
from the next kmem_cache_alloc() call.


> Every idr use I've seen could just do the whole thing
> under a mutex and not worry about the awkward retry idea.
Unfortunately there are some users that do idr_get_new() within a spinlock.
e.g. from drivers/gpu/drm/drm_gem.c:
>         if (idr_pre_get(&file_priv->object_idr, GFP_KERNEL) == 0)
>                 return -ENOMEM;
>
>         /* do the allocation under our spinlock */
>         spin_lock(&file_priv->table_lock);
>         ret = idr_get_new_above(&file_priv->object_idr, obj, 1, handlep);
>         spin_unlock(&file_priv->table_lock);
:-(

--
    Manfred
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