[PATCH v2] mm/hotplug: treat CMA pages as unmovable

[Qian Cai]

has_unmovable_pages() is used by allocating CMA and gigantic pages as
well as the memory hotplug. The later doesn't know how to offline CMA
pool properly now, but if an unused (free) CMA page is encountered, then
has_unmovable_pages() happily considers it as a free memory and
propagates this up the call chain. Memory offlining code then frees the
page without a proper CMA tear down which leads to an accounting issues.
Moreover if the same memory range is onlined again then the memory never
gets back to the CMA pool.

State after memory offline:
 # 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@xxxxxx>
---

v2: Borrow some commit log texts from Michal.
    Call dump_page() in the error path per Michal.

 mm/page_alloc.c | 30 ++++++++++++++++++------------
 1 file changed, 18 insertions(+), 12 deletions(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index d96ca5bc555b..a9d2b0236167 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -8005,7 +8005,10 @@ void *__init alloc_large_system_hash(const char *tablename,
 bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
 			 int migratetype, int flags)
 {
-	unsigned long pfn, iter, found;
+	unsigned long found;
+	unsigned long iter = 0;
+	unsigned long pfn = page_to_pfn(page);
+	char reason[] = "unmovable page";
 
 	/*
 	 * TODO we could make this much more efficient by not checking every
@@ -8015,17 +8018,20 @@ 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;
+
+		strscpy(reason, "CMA page", 9);
+		goto unmovable;
+	}
 
-	pfn = page_to_pfn(page);
-	for (found = 0, iter = 0; iter < pageblock_nr_pages; iter++) {
+	for (found = 0; iter < pageblock_nr_pages; iter++) {
 		unsigned long check = pfn + iter;
 
 		if (!pfn_valid_within(check))
@@ -8105,7 +8111,7 @@ bool has_unmovable_pages(struct zone *zone, struct page *page, int count,
 unmovable:
 	WARN_ON_ONCE(zone_idx(zone) == ZONE_MOVABLE);
 	if (flags & REPORT_FAILURE)
-		dump_page(pfn_to_page(pfn+iter), "unmovable page");
+		dump_page(pfn_to_page(pfn+iter), reason);
 	return true;
 }
 
-- 
2.20.1 (Apple Git-117)