[PATCHv3] mm: page_alloc: fix CMA area initialisation when pageblock > MAX_ORDER

[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.

Cc: stable at vger.kernel.org
Signed-off-by: Michal Nazarewicz <mina86 at mina86.com>
Reported-by: Mark Salter <msalter at redhat.com>
Tested-by: Christopher Covington <cov at codeaurora.org>
---
 mm/page_alloc.c | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

 Mark Salter wrote:
 > I ended up needing this (on top of your patch) to get the system to
 > boot.  Each MAX_ORDER-1 group needs the refcount and migratetype set
 > so that __free_pages does the right thing.
 >
 > diff --git a/mm/page_alloc.c b/mm/page_alloc.c
 > index 02fb1ed..a7ca6cc 100644
 > --- a/mm/page_alloc.c
 > +++ b/mm/page_alloc.c
 > @@ -799,17 +799,18 @@ void __init init_cma_reserved_pageblock(struct page *page)
 >  		set_page_count(p, 0);
 >  	} while (++p, --i);
 >  
 > -	set_page_refcounted(page);
 > -	set_pageblock_migratetype(page, MIGRATE_CMA);
 > -
 > -	if (pageblock_order > MAX_ORDER) {
 > -		i = pageblock_order - MAX_ORDER;
 > +	if (pageblock_order >= MAX_ORDER) {
 > +		i = pageblock_order - MAX_ORDER + 1;
 >  		i = 1 << i;
 >  		p = page;
 >  		do {
 > -			__free_pages(p, MAX_ORDER);
 > +			set_page_refcounted(p);
 > +			set_pageblock_migratetype(p, MIGRATE_CMA);
 > +			__free_pages(p, MAX_ORDER - 1);
 >  		} while (p += MAX_ORDER_NR_PAGES, --i);
 >  	} else {
 > +		set_page_refcounted(page);
 > +		set_pageblock_migratetype(page, MIGRATE_CMA);
 >  		__free_pages(page, pageblock_order);
 >  	}

 This is kinda embarrassing, dunno how I missed that.

 But each page actually does not need to have migratetype set, does it?
 All of those pages are in a single pageblock so a single call
 suffices.  If you track set_pageblock_migratetype down to pfn_to_bitidx
 there is:

	return (pfn >> pageblock_order) * NR_PAGEBLOCK_BITS;

 so for pfns inside of a pageblock, they get truncated.  Or did I miss
 yet another thing?

diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index ee92384..fef9614 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -816,9 +816,21 @@ void __init init_cma_reserved_pageblock(struct page *page)
 		set_page_count(p, 0);
 	} while (++p, --i);
 
-	set_page_refcounted(page);
 	set_pageblock_migratetype(page, MIGRATE_CMA);
-	__free_pages(page, pageblock_order);
+
+	if (pageblock_order >= MAX_ORDER) {
+		i = pageblock_nr_pages;
+		p = page;
+		do {
+			set_page_refcounted(p);
+			__free_pages(p, MAX_ORDER - 1);
+			p += MAX_ORDER_NR_PAGES;
+		} while (i -= MAX_ORDER_NR_PAGES);
+	} else {
+		set_page_refcounted(page);
+		__free_pages(page, pageblock_order);
+	}
+
 	adjust_managed_page_count(page, pageblock_nr_pages);
 }
 #endif
-- 
2.0.0.526.g5318336