[PATCH] mm: fix maybe-uninitialized warning in section_deactivate()

[Arnd Bergmann]

gcc cannot track the combined state of the 'mask' variable across the
barrier in pgdat_resize_unlock() at compile time, so it warns that we
can run into undefined behavior:

mm/sparse.c: In function 'section_deactivate':
mm/sparse.c:802:7: error: 'early_section' may be used uninitialized in this 
function [-Werror=maybe-uninitialized]

We know that this can't happen because the spin_unlock() doesn't
affect the mask variable, so this is a false-postive warning, but
rearranging the code to bail out earlier here makes it obvious
to the compiler as well.

Fixes: mmotm ("mm: support section-unaligned ZONE_DEVICE memory ranges")
Signed-off-by: Arnd Bergmann <a...@arndb.de>
---
 mm/sparse.c | 33 +++++++++++++++++----------------
 1 file changed, 17 insertions(+), 16 deletions(-)

diff --git a/mm/sparse.c b/mm/sparse.c
index 4267d09b656b..dd0c2dd08ee2 100644
--- a/mm/sparse.c
+++ b/mm/sparse.c
@@ -807,23 +807,24 @@ static void section_deactivate(struct pglist_data *pgdat, 
unsigned long pfn,
        unsigned long mask = section_active_mask(pfn, nr_pages), flags;
 
        pgdat_resize_lock(pgdat, &flags);
-       if (!ms->usage) {
-               mask = 0;
-       } else if ((ms->usage->map_active & mask) != mask) {
-               WARN(1, "section already deactivated active: %#lx mask: %#lx\n",
-                               ms->usage->map_active, mask);
-               mask = 0;
-       } else {
-               early_section = is_early_section(ms);
-               ms->usage->map_active ^= mask;
-               if (ms->usage->map_active == 0) {
-                       usage = ms->usage;
-                       ms->usage = NULL;
-                       memmap = sparse_decode_mem_map(ms->section_mem_map,
-                                       section_nr);
-                       ms->section_mem_map = 0;
-               }
+       if (!ms->usage ||
+           WARN((ms->usage->map_active & mask) != mask,
+                "section already deactivated active: %#lx mask: %#lx\n",
+                       ms->usage->map_active, mask)) {
+               pgdat_resize_unlock(pgdat, &flags);
+               return;
        }
+
+       early_section = is_early_section(ms);
+       ms->usage->map_active ^= mask;
+       if (ms->usage->map_active == 0) {
+               usage = ms->usage;
+               ms->usage = NULL;
+               memmap = sparse_decode_mem_map(ms->section_mem_map,
+                               section_nr);
+               ms->section_mem_map = 0;
+       }
+
        pgdat_resize_unlock(pgdat, &flags);
 
        /*
-- 
2.9.0