mm/cma_debug: fix invalid accesses for inactive CMA areas

cma_activate_area() can fail after allocating range bitmaps.  Its cleanup
path frees those bitmaps, but only clears cma->count and
cma->available_count.  It leaves cma->nranges and each range's count in
place, so cma_debugfs_init() can still register debugfs files for an area
that never activated successfully.

That exposes two problems.  Reading the bitmap file can make debugfs walk
a freed range bitmap and trigger an invalid memory access.  Reading
maxchunk can also take cma->lock even though that lock is initialized only
on the successful activation path.

Fix this by creating debugfs entries only for CMA areas that reached
CMA_ACTIVATED.

c009da4258 introduced the invalid access to bitmap file.  2e32b94760
introduced the invalid access to cma->lock.  This change applies to both
issues.  So I added two Fixes tags.

Link: https://lore.kernel.org/20260520061025.3971821-1-songmuchun@bytedance.com
Fixes: c009da4258 ("mm, cma: support multiple contiguous ranges, if requested")
Fixes: 2e32b94760 ("mm: cma: add functions to get region pages counters")
Signed-off-by: Muchun Song <songmuchun@bytedance.com>
Acked-by: Mike Rapoport (Microsoft) <rppt@kernel.org>
Acked-by: Oscar Salvador (SUSE) <osalvador@kernel.org>
Acked-by: David Hildenbrand (Arm) <david@kernel.org>
Cc: Dmitry Safonov <0x7f454c46@gmail.com>
Cc: Frank van der Linden <fvdl@google.com>
Cc: Liam R. Howlett <liam@infradead.org>
Cc: Lorenzo Stoakes <ljs@kernel.org>
Cc: Michal Hocko <mhocko@suse.com>
Cc: Michal Nazarewicz <mina86@mina86.com>
Cc: Stefan Strogin <stefan.strogin@gmail.com>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Vlastimil Babka <vbabka@kernel.org>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

mm/cma_debug.c

@@ -205,7 +205,8 @@ static int __init cma_debugfs_init(void)
 	cma_debugfs_root = debugfs_create_dir("cma", NULL);
 
 	for (i = 0; i < cma_area_count; i++)
-		cma_debugfs_add_one(&cma_areas[i], cma_debugfs_root);
+		if (test_bit(CMA_ACTIVATED, &cma_areas[i].flags))
+			cma_debugfs_add_one(&cma_areas[i], cma_debugfs_root);
 
 	return 0;
 }