linux-kernel - [PATCH] mm/sparse: fix a bad comparison

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Message-Id: <20190228181839.86504-1-cai@lca.pw>
Date:   Thu, 28 Feb 2019 13:18:39 -0500
From:   Qian Cai <cai@....pw>
To:     akpm@...ux-foundation.org
Cc:     dave.hansen@...ux.intel.com, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, Qian Cai <cai@....pw>
Subject: [PATCH] mm/sparse: fix a bad comparison

next_present_section_nr() could only return an unsigned number -1, so
just check it specifically where compilers will convert -1 to unsigned
if needed.

mm/sparse.c: In function 'sparse_init_nid':
mm/sparse.c:200:20: warning: comparison of unsigned expression >= 0 is
always true [-Wtype-limits]
       ((section_nr >= 0) &&    \
                    ^~
mm/sparse.c:478:2: note: in expansion of macro
'for_each_present_section_nr'
  for_each_present_section_nr(pnum_begin, pnum) {
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~
mm/sparse.c:200:20: warning: comparison of unsigned expression >= 0 is
always true [-Wtype-limits]
       ((section_nr >= 0) &&    \
                    ^~
mm/sparse.c:497:2: note: in expansion of macro
'for_each_present_section_nr'
  for_each_present_section_nr(pnum_begin, pnum) {
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~
mm/sparse.c: In function 'sparse_init':
mm/sparse.c:200:20: warning: comparison of unsigned expression >= 0 is
always true [-Wtype-limits]
       ((section_nr >= 0) &&    \
                    ^~
mm/sparse.c:520:2: note: in expansion of macro
'for_each_present_section_nr'
  for_each_present_section_nr(pnum_begin + 1, pnum_end) {
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~

Fixes: c4e1be9ec113 ("mm, sparsemem: break out of loops early")
Signed-off-by: Qian Cai <cai@....pw>
---
 mm/sparse.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/sparse.c b/mm/sparse.c
index 7ea5dc6c6b19..77a0554fa5bd 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -197,7 +197,7 @@ static inline int next_present_section_nr(int section_nr)
 }
 #define for_each_present_section_nr(start, section_nr)		\
 	for (section_nr = next_present_section_nr(start-1);	\
-	     ((section_nr >= 0) &&				\
+	     ((section_nr != -1) &&				\
 	      (section_nr <= __highest_present_section_nr));	\
 	     section_nr = next_present_section_nr(section_nr))
 
-- 
2.17.2 (Apple Git-113)