Re: [PATCH] lib/idr.c: Zero memory properly in idr_remove_all

[Manfred Spraul <manfred@colorfullife.com>]

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