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 <arnd@xxxxxxxx>
---
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
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