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Subject[PATCH 1/3 fix] mm,thp,rmap: subpages_mapcount of PTE-mapped subpages: fix
Yu Zhao reports compiler warning in page_add_anon_rmap():

mm/rmap.c:1236:13: warning: variable 'first' is used uninitialized
whenever 'if' condition is false [-Wsometimes-uninitialized]
} else if (PageTransHuge(page)) {
^~~~~~~~~~~~~~~~~~~
mm/rmap.c:1248:18: note: uninitialized use occurs here
VM_BUG_ON_PAGE(!first && (flags & RMAP_EXCLUSIVE), page);
^~~~~

We do need to fix that, even though it's only uninitialized in an
impossible condition: I've chosen to initialize "first" true, to
minimize the BUGs it might then hit; but you could just as well
choose to initialize it false, to maximize the BUGs it might hit.

Reported-by: Yu Zhao <yuzhao@google.com>
Signed-off-by: Hugh Dickins <hughd@google.com>
---
mm/rmap.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/mm/rmap.c b/mm/rmap.c
index 66be8cae640f..25b720d5ba17 100644
--- a/mm/rmap.c
+++ b/mm/rmap.c
@@ -1281,7 +1281,7 @@ void page_add_anon_rmap(struct page *page,
struct compound_mapcounts mapcounts;
int nr = 0, nr_pmdmapped = 0;
bool compound = flags & RMAP_COMPOUND;
- bool first;
+ bool first = true;

if (unlikely(PageKsm(page)))
lock_page_memcg(page);
--
2.35.3
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