revert "highmem: catch illegal nesting"

Revert

	commit 656dad312fb41ed95ef08325e9df9bece3aacbbb
	Author: Ingo Molnar <mingo@elte.hu>
	Date:   Sat Feb 10 01:46:36 2007 -0800

	[PATCH] highmem: catch illegal nesting

	Catch illegally nested kmap_atomic()s even if the page that is mapped by
	the 'inner' instance is from lowmem.

	This avoids spuriously zapped kmap-atomic ptes and turns hard to find
	crashes into clear asserts at the bug site.

Problem is, a get_zeroed_page(GFP_KERNEL) from interrupt context will trigger
this check if non-irq code on this CPU holds a KM_USER0 mapping.  But that
get_zeroed_page() will never be altering the kmap slot anyway due to the
GFP_KERNEL.

Cc: Christoph Lameter <clameter@sgi.com>
Cc: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 3 insertions, 4 deletions

diff --git a/arch/i386/mm/highmem.c b/arch/i386/mm/highmem.c
index ad8d86cc683e..1c3bf95f7356 100644
--- a/arch/i386/mm/highmem.c
+++ b/arch/i386/mm/highmem.c
@@ -34,17 +34,16 @@ void *kmap_atomic_prot(struct page *page, enum km_type type, pgprot_t prot)
         /* even !CONFIG_PREEMPT needs this, for in_atomic in do_page_fault */
         pagefault_disable();
 
-        idx = type + KM_TYPE_NR*smp_processor_id();
-        BUG_ON(!pte_none(*(kmap_pte-idx)));
-
         if (!PageHighMem(page))
                 return page_address(page);
 
+        idx = type + KM_TYPE_NR*smp_processor_id();
         vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);
+        BUG_ON(!pte_none(*(kmap_pte-idx)));
         set_pte(kmap_pte-idx, mk_pte(page, prot));
         arch_flush_lazy_mmu_mode();
 
-        return (void*) vaddr;
+        return (void *)vaddr;
 }
 
 void *kmap_atomic(struct page *page, enum km_type type)