mm/page_isolation: Fix an infinite loop in isolate_single_pageblock()

HugeTLB allocation (32MB pages on 4K base page) via sysfs on arm64 platform
is getting stuck in isolate_single_pageblock(), because of an infinite loop
Because head_pfn always evaluate the same, so does pfn, and the outer loop
never exits. Dropping the relevant code block, which seems redundant, makes
the problem go away.

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Zi Yan <ziy@nvidia.com>
Cc: linux-mm@kvack.org
Cc: linux-kernel@vger.kernel.org
Fixes: b2c9e2f ("mm: make alloc_contig_range work at pageblock granularity")
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>

mm/page_isolation.c

@@ -389,10 +389,6 @@ static int isolate_single_pageblock(unsigned long boundary_pfn, int flags,
 			struct page *head = compound_head(page);
 			unsigned long head_pfn = page_to_pfn(head);
 
-			if (head_pfn + nr_pages <= boundary_pfn) {
-				pfn = head_pfn + nr_pages;
-				continue;
-			}
 #if defined CONFIG_COMPACTION || defined CONFIG_CMA
 			/*
 			 * hugetlb, lru compound (THP), and movable compound pages