linux-kernel - [PATCH 4.19 023/187] mm/sparse: fix a bad comparison

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Date:   Thu,  4 Apr 2019 10:46:00 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        stable@...r.kernel.org, Qian Cai <cai@....pw>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Sasha Levin <sashal@...nel.org>
Subject: [PATCH 4.19 023/187] mm/sparse: fix a bad comparison

4.19-stable review patch.  If anyone has any objections, please let me know.

------------------

[ Upstream commit d778015ac95bc036af73342c878ab19250e01fe1 ]

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) {
    ^~~~~~~~~~~~~~~~~~~~~~~~~~~

Link: http://lkml.kernel.org/r/20190228181839.86504-1-cai@lca.pw
Fixes: c4e1be9ec113 ("mm, sparsemem: break out of loops early")
Signed-off-by: Qian Cai <cai@....pw>
Reviewed-by: Andrew Morton <akpm@...ux-foundation.org>
Cc: Dave Hansen <dave.hansen@...ux.intel.com>
Signed-off-by: Andrew Morton <akpm@...ux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@...ux-foundation.org>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 mm/sparse.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/sparse.c b/mm/sparse.c
index 10b07eea9a6e..45950a074bdb 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -196,7 +196,7 @@ 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))
 
-- 
2.19.1