i386: Another case of i386 exploiting page sized special casing

i386 uses kmalloc to allocage the thread structure assuming that the allocation
results in a page sized aligned allocation. That has worked so far because SLAB
exempts page sized slabs from debugging and aligns them in special ways that go
beyond the restrictions imposed by KMALLOC_ARCH_MINALIGN.

SLUB also works fine since the page sized allocations neatly align at page
boundaries. However, if debugging is switched on then SLUB will only follow
the requirements imposed by KMALLOC_ARCH_MINALIGN and not preserve page sized
alignment.

So this fix is necessary for SLUB debug to work cleanly with i386 code.

The solution here is to replace the called to kmalloc with calles into the
page allocator. An alternate solution may be to create a custom slab cache
where the alignment is set to PAGE_SIZE (no problem here with page_struct
modifications). That would allow slub debugging to be applied to the
threadinfo structure.

Signed-off-by: Christoph Lameter <clameter@sgi.com>

Index: linux-2.6.21-rc5-mm4/include/asm-i386/thread_info.h
===================================================================
--- linux-2.6.21-rc5-mm4.orig/include/asm-i386/thread_info.h	2007-04-03 23:48:34.000000000 -0700
+++ linux-2.6.21-rc5-mm4/include/asm-i386/thread_info.h	2007-04-04 17:33:41.000000000 -0700
@@ -95,12 +95,14 @@ static inline struct thread_info *curren
 
 /* thread information allocation */
 #ifdef CONFIG_DEBUG_STACK_USAGE
-#define alloc_thread_info(tsk) kzalloc(THREAD_SIZE, GFP_KERNEL)
+#define alloc_thread_info(tsk) ((struct thread_info *) \
+	__get_free_pages(GFP_KERNEL| __GFP_ZERO, get_order(THREAD_SIZE)))
 #else
-#define alloc_thread_info(tsk) kmalloc(THREAD_SIZE, GFP_KERNEL)
+#define alloc_thread_info(tsk) ((struct thread_info *) \
+	__get_free_pages(GFP_KERNEL, get_order(THREAD_SIZE)))
 #endif
 
-#define free_thread_info(info)	kfree(info)
+#define free_thread_info(info)	free_pages((unsigned long)(info), get_order(THREAD_SIZE))
 
 #else /* !__ASSEMBLY__ */