Re: build error: sparsemem + SLOB

Matt Mackall
2006-11-21T19:14:10Z

On Tue, Nov 21, 2006 at 02:57:23PM +0900, Yasunori Goto wrote:
> > On Mon, Nov 20, 2006 at 05:28:24PM +0000, Hugh Dickins wrote:
> > > 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.
> >
> > SLOB is an O(N) allocator and is pretty poorly suited to running on
> > anything like a modern desktop. Disallowing if SMP is probably
> > reasonable, as even machines with multicore ARM or MIPS will probably
> > have enough memory to make SLOB a bit painful.
>
> Ok. It's simple. This is fix.

Are there any implications for preemptible kernels here?

--
Mathematics is the supreme nostalgia of our time.