[PATCH] mm/cma_sysfs: Skip inactive CMA areas in sysfs

[Kaitao Cheng <kaitao.cheng@linux.dev>]

From: Kaitao Cheng <chengkaitao@kylinos.cn>

cma_activate_area() can fail after a CMA area has already been added to
cma_areas[].  In that case the area is left in the global array, but it
does not reach the point where CMA_ACTIVATED is set.

cma_sysfs_init() currently walks all cma_area_count entries and creates
sysfs files for every area, including ones that failed activation. These
areas are not usable CMA areas and should not be exposed to userspace as
valid CMA regions.

If such an inactive area is exposed, userspace sees a CMA directory whose
read-only accounting files report zeros.  total_pages and available_pages
report zero because the failed activation path clears cma->count and
cma->available_count, while the allocation and release counters also stay
at zero because the area cannot service CMA allocations.  This makes the
failed area look like a valid but empty CMA region and can mislead tests,
monitoring, and diagnostics.

Skip CMA areas that did not reach CMA_ACTIVATED when creating the sysfs
objects.  Since inactive entries can now be skipped, make the error
unwind tolerate entries that never had cma_kobj initialized.

Suggested-by: David Hildenbrand (Arm) <david@kernel.org>
Suggested-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Muchun Song <muchun.song@linux.dev>
Signed-off-by: Kaitao Cheng <chengkaitao@kylinos.cn>
---
Changelog:
Changes in v2:
- Revise commit log

Link to v1:
https://lore.kernel.org/linux-mm/20260522131434.78532-1-kaitao.cheng@linux.dev/
---
 mm/cma_sysfs.c | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/mm/cma_sysfs.c b/mm/cma_sysfs.c
index f52b696bc46d..d5bf792c6245 100644
--- a/mm/cma_sysfs.c
+++ b/mm/cma_sysfs.c
@@ -117,13 +117,16 @@ static int __init cma_sysfs_init(void)
 		return -ENOMEM;
 
 	for (i = 0; i < cma_area_count; i++) {
+		cma = &cma_areas[i];
+		if (!test_bit(CMA_ACTIVATED, &cma->flags))
+			continue;
+
 		cma_kobj = kzalloc_obj(*cma_kobj);
 		if (!cma_kobj) {
 			err = -ENOMEM;
 			goto out;
 		}
 
-		cma = &cma_areas[i];
 		cma->cma_kobj = cma_kobj;
 		cma_kobj->cma = cma;
 		err = kobject_init_and_add(&cma_kobj->kobj, &cma_ktype,
@@ -138,7 +141,8 @@ static int __init cma_sysfs_init(void)
 out:
 	while (--i >= 0) {
 		cma = &cma_areas[i];
-		kobject_put(&cma->cma_kobj->kobj);
+		if (cma->cma_kobj)
+			kobject_put(&cma->cma_kobj->kobj);
 	}
 	kobject_put(cma_kobj_root);
 
-- 
2.50.1 (Apple Git-155)