[PATCHv2] mm: page_alloc: fix CMA area initialisation when pageblock > MAX_ORDER

[mina86@mina86.com (Michal Nazarewicz)]

With a kernel configured with ARM64_64K_PAGES && !TRANSPARENT_HUGEPAGE,
the following is triggered at early boot:

  SMP: Total of 8 processors activated.
  devtmpfs: initialized
  Unable to handle kernel NULL pointer dereference at virtual address 00000008
  pgd = fffffe0000050000
  [00000008] *pgd=00000043fba00003, *pmd=00000043fba00003, *pte=00e0000078010407
  Internal error: Oops: 96000006 [#1] SMP
  Modules linked in:
  CPU: 0 PID: 1 Comm: swapper/0 Not tainted 3.15.0-rc864k+ #44
  task: fffffe03bc040000 ti: fffffe03bc080000 task.ti: fffffe03bc080000
  PC is at __list_add+0x10/0xd4
  LR is at free_one_page+0x270/0x638
  ...
  Call trace:
  [<fffffe00003ee970>] __list_add+0x10/0xd4
  [<fffffe000019c478>] free_one_page+0x26c/0x638
  [<fffffe000019c8c8>] __free_pages_ok.part.52+0x84/0xbc
  [<fffffe000019d5e8>] __free_pages+0x74/0xbc
  [<fffffe0000c01350>] init_cma_reserved_pageblock+0xe8/0x104
  [<fffffe0000c24de0>] cma_init_reserved_areas+0x190/0x1e4
  [<fffffe0000090418>] do_one_initcall+0xc4/0x154
  [<fffffe0000bf0a50>] kernel_init_freeable+0x204/0x2a8
  [<fffffe00007520a0>] kernel_init+0xc/0xd4

This happens because init_cma_reserved_pageblock() calls
__free_one_page() with pageblock_order as page order but it is bigger
han MAX_ORDER.  This in turn causes accesses past zone->free_list[].

Fix the problem by changing init_cma_reserved_pageblock() such that it
splits pageblock into individual MAX_ORDER pages if pageblock is
bigger than a MAX_ORDER page.

In cases where !CONFIG_HUGETLB_PAGE_SIZE_VARIABLE, which is all
architectures expect for ia64, powerpc and tile at the moment, the
?pageblock_order > MAX_ORDER? condition will be optimised out since
both sides of the operator are constants.  In cases where pageblock
size is variable, the performance degradation should not be
significant anyway since init_cma_reserved_pageblock() is called
only at boot time at most MAX_CMA_AREAS times which by default is
eight.

Signed-off-by: Michal Nazarewicz <mina86@mina86.com>
Reported-by: Mark Salter <msalter@redhat.com>
---
 mm/page_alloc.c | 13 ++++++++++++-
 1 file changed, 12 insertions(+), 1 deletion(-)

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index 7f97767..fe114db 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -817,7 +817,18 @@ void __init init_cma_reserved_pageblock(struct page *page)
 
 	set_page_refcounted(page);
 	set_pageblock_migratetype(page, MIGRATE_CMA);
-	__free_pages(page, pageblock_order);
+
+	if (pageblock_order > MAX_ORDER) {
+		i = pageblock_order - MAX_ORDER;
+		i = 1 << i;
+		p = page;
+		do {
+			__free_pages(p, MAX_ORDER);
+		} while (p += MAX_ORDER_NR_PAGES, --i);
+	} else {
+		__free_pages(page, pageblock_order);
+	}
+
 	adjust_managed_page_count(page, pageblock_nr_pages);
 }
 #endif
-- 
2.0.0.526.g5318336