Patch "mm/memory_hotplug: set magic number to page->freelist instead of page->lru.next" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

    mm/memory_hotplug: set magic number to page->freelist instead of page->lru.next

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
mm-memory_hotplug-set-magic-number-to-page-freelist-instead-of-page-lru.next.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Yasuaki Ishimatsu <[email protected]>
Date: Wed, 22 Feb 2017 15:45:13 -0800
Subject: mm/memory_hotplug: set magic number to page->freelist instead of page->lru.next

From: Yasuaki Ishimatsu <[email protected]>

[ Upstream commit ddffe98d166f4a93d996d5aa628fd745311fc1e7 ]

To identify that pages of page table are allocated from bootmem allocator, magic number sets to page->lru.next.

But page->lru list is initialized in reserve_bootmem_region(). So when calling free_pagetable(), the function cannot find the magic number of pages. And free_pagetable() frees the pages by free_reserved_page() not put_page_bootmem().

But if the pages are allocated from bootmem allocator and used as page table, the pages have private flag. So before freeing the pages, we should clear the private flag by put_page_bootmem().

Before applying the commit 7bfec6f47bb0 ("mm, page_alloc: check multiple page fields with a single branch"), we could find the following visible issue:

  BUG: Bad page state in process kworker/u1024:1
  page:ffffea103cfd8040 count:0 mapcount:0 mappi
  flags: 0x6fffff80000800(private)
  page dumped because: PAGE_FLAGS_CHECK_AT_FREE flag(s) set
  bad because of flags: 0x800(private)
  <snip>
  Call Trace:
  [...] dump_stack+0x63/0x87
  [...] bad_page+0x114/0x130
  [...] free_pages_prepare+0x299/0x2d0
  [...] free_hot_cold_page+0x31/0x150
  [...] __free_pages+0x25/0x30
  [...] free_pagetable+0x6f/0xb4
  [...] remove_pagetable+0x379/0x7ff
  [...] vmemmap_free+0x10/0x20
  [...] sparse_remove_one_section+0x149/0x180
  [...] __remove_pages+0x2e9/0x4f0
  [...] arch_remove_memory+0x63/0xc0
  [...] remove_memory+0x8c/0xc0
  [...] acpi_memory_device_remove+0x79/0xa5
  [...] acpi_bus_trim+0x5a/0x8d
  [...] acpi_bus_trim+0x38/0x8d
  [...] acpi_device_hotplug+0x1b7/0x418
  [...] acpi_hotplug_work_fn+0x1e/0x29
  [...] process_one_work+0x152/0x400
  [...] worker_thread+0x125/0x4b0
  [...] kthread+0xd8/0xf0
  [...] ret_from_fork+0x22/0x40

And the issue still silently occurs.

Until freeing the pages of page table allocated from bootmem allocator, the page->freelist is never used. So the patch sets magic number to page->freelist instead of page->lru.next.

---
 arch/x86/mm/init_64.c |    2 +-
 mm/memory_hotplug.c   |    5 +++--
 mm/sparse.c           |    2 +-
 3 files changed, 5 insertions(+), 4 deletions(-)

@@ -689,7 +689,7 @@ static void __meminit free_pagetable(str
 	if (PageReserved(page)) {
 		__ClearPageReserved(page);
 
-		magic = (unsigned long)page->lru.next;
+		magic = (unsigned long)page->freelist;
 		if (magic == SECTION_INFO || magic == MIX_SECTION_INFO) {
 			while (nr_pages--)
 				put_page_bootmem(page++);

@@ -179,7 +179,7 @@ static void release_memory_resource(stru
 void get_page_bootmem(unsigned long info,  struct page *page,
 		      unsigned long type)
 {
-	page->lru.next = (struct list_head *) type;
+	page->freelist = (void *)type;
 	SetPagePrivate(page);
 	set_page_private(page, info);
 	page_ref_inc(page);

@@ -189,11 +189,12 @@ void put_page_bootmem(struct page *page)
 {
 	unsigned long type;
 
-	type = (unsigned long) page->lru.next;
+	type = (unsigned long) page->freelist;
 	BUG_ON(type < MEMORY_HOTPLUG_MIN_BOOTMEM_TYPE ||
 	       type > MEMORY_HOTPLUG_MAX_BOOTMEM_TYPE);
 
 	if (page_ref_dec_return(page) == 1) {
+		page->freelist = NULL;
 		ClearPagePrivate(page);
 		set_page_private(page, 0);
 		INIT_LIST_HEAD(&page->lru);

@@ -662,7 +662,7 @@ static void free_map_bootmem(struct page
 		>> PAGE_SHIFT;
 
 	for (i = 0; i < nr_pages; i++, page++) {
-		magic = (unsigned long) page->lru.next;
+		magic = (unsigned long) page->freelist;
 
 		BUG_ON(magic == NODE_INFO);
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/mm-memory_hotplug-set-magic-number-to-page-freelist-instead-of-page-lru.next.patch