Re: build error: sparsemem + SLOB

Hugh Dickins
2006-11-20T17:28:24Z

On Mon, 20 Nov 2006, Christoph Lameter wrote:
>
> As far as I can tell SLOB is fundamentally racy since it does not support
> SLAB_DESTROY_BY_RCU correctly. F.e. The constructor for the anon_vma will
> be called on alloc without regard for RCU, we free an item and reuse it
> without regard to RCU. This can potentially mess up the anon_vma locking
> state while we access it.

Good find!

> Is SLOB used at all or have we been lucky so far?

Lucky so far. Well, we'd actually have to be quite unlucky to ever
see what page_lock_anon_vma/SLAB_DESTROY_BY_RCU are guarding against.

But you're absolutely right that users should not be exposed to such
unsafety. I'd say SLOB should be disallowed if SMP.

Hugh