mm/khugepaged: add missed tracepoint for collapse_huge_page_swapin

One return case of `__collapse_huge_page_swapin()` does not invoke
tracepoint while every other return case does.  This commit adds a
tracepoint invocation for the case.

Link: http://lkml.kernel.org/r/20170507101813.30187-1-sj38.park@gmail.comSigned-off-by: NSeongJae Park <sj38.park@gmail.com>
Cc: Kirill A. Shutemov <kirill.shutemov@linux.intel.com>
Cc: Johannes Weiner <hannes@cmpxchg.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

mm/khugepaged.c

@@ -907,8 +907,10 @@ static bool __collapse_huge_page_swapin(struct mm_struct *mm,
 				return false;
 			}
 			/* check if the pmd is still valid */
-			if (mm_find_pmd(mm, address) != pmd)
+			if (mm_find_pmd(mm, address) != pmd) {
+				trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);
 				return false;
+			}
 		}
 		if (ret & VM_FAULT_ERROR) {
 			trace_mm_collapse_huge_page_swapin(mm, swapped_in, referenced, 0);