[PATCH] mm/hotplug: treat CMA pages as unmovable

[Qian Cai <cai@lca.pw>]

When offlining a memory block that contains reserved CMA areas, it will
set those page blocks migration type as MIGRATE_ISOLATE. Then, onlining
will set them as MIGRATE_MOVABLE. As the results, those page blocks lose
their original types, i.e., MIGRATE_CMA, and then it causes troubles
like accounting for CMA areas becomes inconsist,

 # grep cma /proc/vmstat
 nr_free_cma 205824

 # cat /sys/kernel/debug/cma/cma-kvm_cma/count
 209920

Also, kmemleak still think those memory address are reserved but have
already been used by the buddy allocator after onlining.

Offlined Pages 4096
kmemleak: Cannot insert 0xc000201f7d040008 into the object search tree
(overlaps existing)
Call Trace:
[c00000003dc2faf0] [c000000000884b2c] dump_stack+0xb0/0xf4 (unreliable)
[c00000003dc2fb30] [c000000000424fb4] create_object+0x344/0x380
[c00000003dc2fbf0] [c0000000003d178c] __kmalloc_node+0x3ec/0x860
[c00000003dc2fc90] [c000000000319078] kvmalloc_node+0x58/0x110
[c00000003dc2fcd0] [c000000000484d9c] seq_read+0x41c/0x620
[c00000003dc2fd60] [c0000000004472bc] __vfs_read+0x3c/0x70
[c00000003dc2fd80] [c0000000004473ac] vfs_read+0xbc/0x1a0
[c00000003dc2fdd0] [c00000000044783c] ksys_read+0x7c/0x140
[c00000003dc2fe20] [c00000000000b108] system_call+0x5c/0x70
kmemleak: Kernel memory leak detector disabled
kmemleak: Object 0xc000201cc8000000 (size 13757317120):
kmemleak:   comm "swapper/0", pid 0, jiffies 4294937297
kmemleak:   min_count = -1
kmemleak:   count = 0
kmemleak:   flags = 0x5
kmemleak:   checksum = 0
kmemleak:   backtrace:
     cma_declare_contiguous+0x2a4/0x3b0
     kvm_cma_reserve+0x11c/0x134
     setup_arch+0x300/0x3f8
     start_kernel+0x9c/0x6e8
     start_here_common+0x1c/0x4b0
kmemleak: Automatic memory scanning thread ended

Signed-off-by: Qian Cai <cai@lca.pw>
---
 mm/page_alloc.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d96ca5bc555b..896db9241fa6 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8015,14 +8015,18 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
 	 * can still lead to having bootmem allocations in zone_movable.
 	 */
 
-	/*
-	 * CMA allocations (alloc_contig_range) really need to mark isolate
-	 * CMA pageblocks even when they are not movable in fact so consider
-	 * them movable here.
-	 */
-	if (is_migrate_cma(migratetype) &&
-			is_migrate_cma(get_pageblock_migratetype(page)))
-		return false;
+	if (is_migrate_cma(get_pageblock_migratetype(page))) {
+		/*
+		 * CMA allocations (alloc_contig_range) really need to mark
+		 * isolate CMA pageblocks even when they are not movable in fact
+		 * so consider them movable here.
+		 */
+		if (is_migrate_cma(migratetype))
+			return false;
+
+		pr_warn("page: %px is in CMA", page);
+		return true;
+	}
 
 	pfn = page_to_pfn(page);
 	for (found = 0, iter = 0; iter < pageblock_nr_pages; iter++) {
-- 
2.20.1 (Apple Git-117)