mm/memory-failure.c: move comment

The comment about pages under writeback is far from the relevant code, so
let's move it to the right place.
Signed-off-by: NNaoya Horiguchi <n-horiguchi@ah.jp.nec.com>
Cc: Andi Kleen <andi@firstfloor.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/memory-failure.c

@@ -1132,11 +1132,6 @@ int memory_failure(unsigned long pfn, int trapno, int flags)
 		}
 	}
 
-	/*
-	 * Lock the page and wait for writeback to finish.
-	 * It's very difficult to mess with pages currently under IO
-	 * and in many cases impossible, so we just avoid it here.
-	 */
 	lock_page(hpage);
 
 	/*
@@ -1186,6 +1181,10 @@ int memory_failure(unsigned long pfn, int trapno, int flags)
 	if (PageHuge(p))
 		set_page_hwpoison_huge_page(hpage);
 
+	/*
+	 * It's very difficult to mess with pages currently under IO
+	 * and in many cases impossible, so we just avoid it here.
+	 */
 	wait_on_page_writeback(p);
 
 	/*