powerpc/highmem: Change BUG_ON() to WARN_ON()

In arch/powerpc/mm/highmem.c, BUG_ON() is called only when
CONFIG_DEBUG_HIGHMEM is selected, this means the BUG_ON() is not vital
and can be replaced by a a WARN_ON().

At the same time, use IS_ENABLED() instead of #ifdef to clean a bit.
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>

arch/powerpc/mm/highmem.c

@@ -43,9 +43,7 @@ void *kmap_atomic_prot(struct page *page, pgprot_t prot)
 	type = kmap_atomic_idx_push();
 	idx = type + KM_TYPE_NR*smp_processor_id();
 	vaddr = __fix_to_virt(FIX_KMAP_BEGIN + idx);
-#ifdef CONFIG_DEBUG_HIGHMEM
-	BUG_ON(!pte_none(*(kmap_pte-idx)));
-#endif
+	WARN_ON(IS_ENABLED(CONFIG_DEBUG_HIGHMEM) && !pte_none(*(kmap_pte - idx)));
 	__set_pte_at(&init_mm, vaddr, kmap_pte-idx, mk_pte(page, prot), 1);
 	local_flush_tlb_page(NULL, vaddr);
 
@@ -56,7 +54,6 @@ EXPORT_SYMBOL(kmap_atomic_prot);
 void __kunmap_atomic(void *kvaddr)
 {
 	unsigned long vaddr = (unsigned long) kvaddr & PAGE_MASK;
-	int type __maybe_unused;
 
 	if (vaddr < __fix_to_virt(FIX_KMAP_END)) {
 		pagefault_enable();
@@ -64,14 +61,12 @@ void __kunmap_atomic(void *kvaddr)
 		return;
 	}
 
-	type = kmap_atomic_idx();
-
-#ifdef CONFIG_DEBUG_HIGHMEM
-	{
+	if (IS_ENABLED(CONFIG_DEBUG_HIGHMEM)) {
+		int type = kmap_atomic_idx();
 		unsigned int idx;
 
 		idx = type + KM_TYPE_NR * smp_processor_id();
-		BUG_ON(vaddr != __fix_to_virt(FIX_KMAP_BEGIN + idx));
+		WARN_ON(vaddr != __fix_to_virt(FIX_KMAP_BEGIN + idx));
 
 		/*
 		 * force other mappings to Oops if they'll try to access
@@ -80,7 +75,6 @@ void __kunmap_atomic(void *kvaddr)
 		pte_clear(&init_mm, vaddr, kmap_pte-idx);
 		local_flush_tlb_page(NULL, vaddr);
 	}
-#endif
 
 	kmap_atomic_idx_pop();
 	pagefault_enable();