Re: start_kernel(): bug: interrupts were enabled early

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 01 Apr 2010 12:17:11 +1100 Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote:

> On Wed, 2010-03-31 at 15:49 -0700, Andrew Morton wrote:
> > 
> > But these things are all utterly gross.  The bottom line is that
> > radix_tree_init() is manifestly unsuited to being called with local
> > interrupts disabled.  773e3eb7b81e5ba13b5155dfb3bb75b8ce37f8f9 was
> > just a wrong patch. 
> 
> Except that powerpc (and now it seems x86) both want to use radix trees
> for interrupt handling... At least on powerpc, we trick and use a linear
> search until the radix trees are initialized, which we do later during
> boot, but that somewhat sucks.
> 
> I believe sherry picking things like not calling radix_tree_init() is
> going to fix one case today, until we have another one, and another one,
> and etc...
> 
> I suspect we're better off fixing the root of the problem in down/up.
> 

Not by adding overhead to every single down_read()/down_write() just to
fix a once-off startup problem - that's taking laziness way too far.

We'd be better off hacking a kmem_cache_create() special case to avoid
taking the rwsem.  Add SLAB_I_SUCK to `flags' perhaps.