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memcg: bad page if page_cgroup when free
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Replace free_hot_cold_page's VM_BUG_ON(page_get_page_cgroup(page)) by a "Bad
page state" and clear: most users don't have CONFIG_DEBUG_VM on, and if it
were set here, it'd likely cause corruption when the page is reused.

Don't use page_assign_page_cgroup to clear it: that should be private to
memcontrol.c, and always called with the lock taken; and memmap_init_zone
doesn't need it either - like page->mapping and other pointers throughout the
kernel, Linux assumes pointers in zeroed structures are NULL pointers.

Instead use page_reset_bad_cgroup, added to memcontrol.h for this only.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: David Rientjes <rientjes@google.com>
Acked-by: Balbir Singh <balbir@linux.vnet.ibm.com>
Acked-by: KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com>
Cc: Hirokazu Takahashi <taka@valinux.co.jp>
Cc: YAMAMOTO Takashi <yamamoto@valinux.co.jp>
Cc: Paul Menage <menage@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
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Hugh Dickins authored and Linus Torvalds committed Mar 5, 2008
1 parent 98837c7 commit 9442ec9
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Showing 3 changed files with 28 additions and 25 deletions.
8 changes: 4 additions & 4 deletions include/linux/memcontrol.h
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Original file line number Diff line number Diff line change
Expand Up @@ -29,8 +29,9 @@ struct mm_struct;

extern void mm_init_cgroup(struct mm_struct *mm, struct task_struct *p);
extern void mm_free_cgroup(struct mm_struct *mm);
extern void page_assign_page_cgroup(struct page *page,
struct page_cgroup *pc);

#define page_reset_bad_cgroup(page) ((page)->page_cgroup = 0)

extern struct page_cgroup *page_get_page_cgroup(struct page *page);
extern int mem_cgroup_charge(struct page *page, struct mm_struct *mm,
gfp_t gfp_mask);
Expand Down Expand Up @@ -82,8 +83,7 @@ static inline void mm_free_cgroup(struct mm_struct *mm)
{
}

static inline void page_assign_page_cgroup(struct page *page,
struct page_cgroup *pc)
static inline void page_reset_bad_cgroup(struct page *page)
{
}

Expand Down
27 changes: 12 additions & 15 deletions mm/memcontrol.c
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Original file line number Diff line number Diff line change
Expand Up @@ -140,11 +140,17 @@ struct mem_cgroup {

/*
* We use the lower bit of the page->page_cgroup pointer as a bit spin
* lock. We need to ensure that page->page_cgroup is atleast two
* byte aligned (based on comments from Nick Piggin)
* lock. We need to ensure that page->page_cgroup is at least two
* byte aligned (based on comments from Nick Piggin). But since
* bit_spin_lock doesn't actually set that lock bit in a non-debug
* uniprocessor kernel, we should avoid setting it here too.
*/
#define PAGE_CGROUP_LOCK_BIT 0x0
#define PAGE_CGROUP_LOCK (1 << PAGE_CGROUP_LOCK_BIT)
#if defined(CONFIG_SMP) || defined(CONFIG_DEBUG_SPINLOCK)
#define PAGE_CGROUP_LOCK (1 << PAGE_CGROUP_LOCK_BIT)
#else
#define PAGE_CGROUP_LOCK 0x0
#endif

/*
* A page_cgroup page is associated with every page descriptor. The
Expand Down Expand Up @@ -271,19 +277,10 @@ static inline int page_cgroup_locked(struct page *page)
&page->page_cgroup);
}

void page_assign_page_cgroup(struct page *page, struct page_cgroup *pc)
static void page_assign_page_cgroup(struct page *page, struct page_cgroup *pc)
{
int locked;

/*
* While resetting the page_cgroup we might not hold the
* page_cgroup lock. free_hot_cold_page() is an example
* of such a scenario
*/
if (pc)
VM_BUG_ON(!page_cgroup_locked(page));
locked = (page->page_cgroup & PAGE_CGROUP_LOCK);
page->page_cgroup = ((unsigned long)pc | locked);
VM_BUG_ON(!page_cgroup_locked(page));
page->page_cgroup = ((unsigned long)pc | PAGE_CGROUP_LOCK);
}

struct page_cgroup *page_get_page_cgroup(struct page *page)
Expand Down
18 changes: 12 additions & 6 deletions mm/page_alloc.c
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Original file line number Diff line number Diff line change
Expand Up @@ -222,13 +222,19 @@ static inline int bad_range(struct zone *zone, struct page *page)

static void bad_page(struct page *page)
{
printk(KERN_EMERG "Bad page state in process '%s'\n"
KERN_EMERG "page:%p flags:0x%0*lx mapping:%p mapcount:%d count:%d\n"
KERN_EMERG "Trying to fix it up, but a reboot is needed\n"
KERN_EMERG "Backtrace:\n",
void *pc = page_get_page_cgroup(page);

printk(KERN_EMERG "Bad page state in process '%s'\n" KERN_EMERG
"page:%p flags:0x%0*lx mapping:%p mapcount:%d count:%d\n",
current->comm, page, (int)(2*sizeof(unsigned long)),
(unsigned long)page->flags, page->mapping,
page_mapcount(page), page_count(page));
if (pc) {
printk(KERN_EMERG "cgroup:%p\n", pc);
page_reset_bad_cgroup(page);
}
printk(KERN_EMERG "Trying to fix it up, but a reboot is needed\n"
KERN_EMERG "Backtrace:\n");
dump_stack();
page->flags &= ~(1 << PG_lru |
1 << PG_private |
Expand Down Expand Up @@ -454,6 +460,7 @@ static inline int free_pages_check(struct page *page)
{
if (unlikely(page_mapcount(page) |
(page->mapping != NULL) |
(page_get_page_cgroup(page) != NULL) |
(page_count(page) != 0) |
(page->flags & (
1 << PG_lru |
Expand Down Expand Up @@ -603,6 +610,7 @@ static int prep_new_page(struct page *page, int order, gfp_t gfp_flags)
{
if (unlikely(page_mapcount(page) |
(page->mapping != NULL) |
(page_get_page_cgroup(page) != NULL) |
(page_count(page) != 0) |
(page->flags & (
1 << PG_lru |
Expand Down Expand Up @@ -989,7 +997,6 @@ static void free_hot_cold_page(struct page *page, int cold)

if (!PageHighMem(page))
debug_check_no_locks_freed(page_address(page), PAGE_SIZE);
VM_BUG_ON(page_get_page_cgroup(page));
arch_free_page(page, 0);
kernel_map_pages(page, 1, 0);

Expand Down Expand Up @@ -2528,7 +2535,6 @@ void __meminit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
set_page_links(page, zone, nid, pfn);
init_page_count(page);
reset_page_mapcount(page);
page_assign_page_cgroup(page, NULL);
SetPageReserved(page);

/*
Expand Down

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