[PATCH 3/3] mm/page_owner: track page free call chain

Sergey Senozhatsky
2016-07-11T14:28:34Z

Extend page_owner with free_pages() tracking functionality. This adds to the
dump_page_owner() output an additional backtrace, that tells us what path has
freed the page.

Aa a trivial example, let's assume that do_some_foo() has an error - an extra
put_page() on error return path, and the function is also getting preempted,
letting some other task to allocate the same page, which is then 'mistakenly'
getting freed once again by do_some_foo().

CPUA CPUB

void do_some_foo(void)
{
page = alloc_page();
if (error) {
put_page(page);
goto out;
}
...
out:
<<preempted>>
void do_some_bar()
{
page = alloc_page();
...
<<preempted>>
...
put_page(page);
}
<<use freed page>>
put_page(page);
}

With the existing implementation we would see only CPUB's backtrace
from bad_page. The extended page_owner would also report CPUA's
put_page(), which can be a helpful hint.

Backtrace:

BUG: Bad page state in process cc1 pfn:bae1d
page:ffffea0002eb8740 count:-1 mapcount:0 mapping: (null) index:0x0
flags: 0x4000000000000000()
page dumped because: nonzero _count
page allocated via order 0, migratetype Unmovable, gfp_mask 0x2000200(GFP_NOWAIT|__GFP_NOWARN)
[<ffffffff8101bc9c>] save_stack_trace+0x26/0x41
[<ffffffff81110fe4>] save_stack+0x46/0xc3
[<ffffffff81111481>] __page_owner_alloc_pages+0x24/0x41
[<ffffffff810c9867>] post_alloc_hook+0x1e/0x20
[<ffffffff810ca63d>] get_page_from_freelist+0x4fd/0x756
[<ffffffff810cadea>] __alloc_pages_nodemask+0xe7/0xbcf
[<ffffffff810cb8e4>] __get_free_pages+0x12/0x40
[<ffffffff810e6b64>] __tlb_remove_page_size.part.12+0x37/0x78
[<ffffffff810e6d9b>] __tlb_remove_page_size+0x21/0x23
[<ffffffff810e7ff2>] unmap_page_range+0x63a/0x75b
[<ffffffff810e81cf>] unmap_single_vma+0xbc/0xc6
[<ffffffff810e82d2>] unmap_vmas+0x35/0x44
[<ffffffff810ee6f4>] exit_mmap+0x5a/0xec
[<ffffffff810385b4>] mmput+0x4a/0xdc
[<ffffffff8103dff7>] do_exit+0x398/0x8de
[<ffffffff8103e5ae>] do_group_exit+0x45/0xb0
page freed, was allocated via order 0, migratetype Unmovable, gfp_mask 0x2000200(GFP_NOWAIT|__GFP_NOWARN)
[<ffffffff8101bc9c>] save_stack_trace+0x26/0x41
[<ffffffff81110fe4>] save_stack+0x46/0xc3
[<ffffffff81111411>] __page_owner_free_pages+0x25/0x71
[<ffffffff810c9f0a>] free_hot_cold_page+0x1d6/0x1ea
[<ffffffff810d03e1>] __put_page+0x37/0x3a
[<ffffffff8115b8da>] do_some_foo()+0x8a/0x8e
...
Modules linked in: ....
CPU: 3 PID: 1274 Comm: cc1 Not tainted 4.7.0-rc5-next-20160701-dbg-00009-ge01494f-dirty #535
0000000000000000 ffff8800aeea3c18 ffffffff811e67ca ffffea0002eb8740
ffffffff8175675e ffff8800aeea3c40 ffffffff810c87f5 0000000000000000
ffffffff81880b40 ffff880137d98438 ffff8800aeea3c50 ffffffff810c88d5
Call Trace:
[<ffffffff811e67ca>] dump_stack+0x68/0x92
[<ffffffff810c87f5>] bad_page+0xf8/0x11e
[<ffffffff810c88d5>] check_new_page_bad+0x63/0x65
[<ffffffff810ca36a>] get_page_from_freelist+0x22a/0x756
[<ffffffff810cadea>] __alloc_pages_nodemask+0xe7/0xbcf
[<ffffffff81073a43>] ? trace_hardirqs_on_caller+0x16d/0x189
[<ffffffff810ede8d>] ? vma_merge+0x159/0x249
[<ffffffff81074aa0>] ? __lock_acquire+0x2ac/0x15c7
[<ffffffff81034ace>] pte_alloc_one+0x1b/0x67
[<ffffffff810e922b>] __pte_alloc+0x19/0xa6
[<ffffffff810eb09f>] handle_mm_fault+0x409/0xc59
[<ffffffff810309f6>] __do_page_fault+0x1d8/0x3ac
[<ffffffff81030bf7>] do_page_fault+0xc/0xe
[<ffffffff814a84af>] page_fault+0x1f/0x30

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
---
include/linux/page_ext.h | 11 ++++++-
mm/page_owner.c | 74 ++++++++++++++++++++++++++++++------------------
2 files changed, 56 insertions(+), 29 deletions(-)

diff --git a/include/linux/page_ext.h b/include/linux/page_ext.h
index 66ba2bb..0cccc94 100644
--- a/include/linux/page_ext.h
+++ b/include/linux/page_ext.h
@@ -27,12 +27,21 @@ enum page_ext_flags {
PAGE_EXT_DEBUG_POISON, /* Page is poisoned */
PAGE_EXT_DEBUG_GUARD,
PAGE_EXT_OWNER_ALLOC,
+ PAGE_EXT_OWNER_FREE,
#if defined(CONFIG_IDLE_PAGE_TRACKING) && !defined(CONFIG_64BIT)
PAGE_EXT_YOUNG,
PAGE_EXT_IDLE,
#endif
};

+#ifdef CONFIG_PAGE_OWNER
+enum page_owner_handles {
+ PAGE_OWNER_HANDLE_ALLOC,
+ PAGE_OWNER_HANDLE_FREE,
+ PAGE_OWNER_HANDLE_MAX
+};
+#endif
+
/*
* Page Extension can be considered as an extended mem_map.
* A page_ext page is associated with every page descriptor. The
@@ -46,7 +55,7 @@ struct page_ext {
unsigned int order;
gfp_t gfp_mask;
int last_migrate_reason;
- depot_stack_handle_t handle;
+ depot_stack_handle_t handles[PAGE_OWNER_HANDLE_MAX];
#endif
};

diff --git a/mm/page_owner.c b/mm/page_owner.c
index 4acccb7..c431ac4 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -13,6 +13,11 @@

#define PAGE_OWNER_STACK_DEPTH (16)

+static const char *page_owner_handles_names[PAGE_OWNER_HANDLE_MAX] = {
+ "page allocated",
+ "page freed, was allocated",
+};
+
static bool page_owner_disabled = true;
DEFINE_STATIC_KEY_FALSE(page_owner_inited);

@@ -85,19 +90,6 @@ struct page_ext_operations page_owner_ops = {
.init = init_page_owner,
};

-void __page_owner_free_pages(struct page *page, unsigned int order)
-{
- int i;
- struct page_ext *page_ext;
-
- for (i = 0; i < (1 << order); i++) {
- page_ext = lookup_page_ext(page + i);
- if (unlikely(!page_ext))
- continue;
- __clear_bit(PAGE_EXT_OWNER_ALLOC, &page_ext->flags);
- }
-}
-
static inline bool check_recursive_alloc(struct stack_trace *trace,
unsigned long ip)
{
@@ -147,6 +139,23 @@ static noinline depot_stack_handle_t save_stack(gfp_t flags)
return handle;
}

+void __page_owner_free_pages(struct page *page, unsigned int order)
+{
+ int i;
+ depot_stack_handle_t handle = save_stack(0);
+
+ for (i = 0; i < (1 << order); i++) {
+ struct page_ext *page_ext = lookup_page_ext(page + i);
+
+ if (unlikely(!page_ext))
+ continue;
+
+ page_ext->handles[PAGE_OWNER_HANDLE_FREE] = handle;
+ __set_bit(PAGE_EXT_OWNER_FREE, &page_ext->flags);
+ __clear_bit(PAGE_EXT_OWNER_ALLOC, &page_ext->flags);
+ }
+}
+
noinline void __page_owner_alloc_pages(struct page *page, unsigned int order,
gfp_t gfp_mask)
{
@@ -155,7 +164,7 @@ noinline void __page_owner_alloc_pages(struct page *page, unsigned int order,
if (unlikely(!page_ext))
return;

- page_ext->handle = save_stack(gfp_mask);
+ page_ext->handles[PAGE_OWNER_HANDLE_ALLOC] = save_stack(gfp_mask);
page_ext->order = order;
page_ext->gfp_mask = gfp_mask;
page_ext->last_migrate_reason = -1;
@@ -189,6 +198,7 @@ void __copy_page_owner(struct page *oldpage, struct page *newpage)
{
struct page_ext *old_ext = lookup_page_ext(oldpage);
struct page_ext *new_ext = lookup_page_ext(newpage);
+ int i;

if (unlikely(!old_ext || !new_ext))
return;
@@ -196,7 +206,9 @@ void __copy_page_owner(struct page *oldpage, struct page *newpage)
new_ext->order = old_ext->order;
new_ext->gfp_mask = old_ext->gfp_mask;
new_ext->last_migrate_reason = old_ext->last_migrate_reason;
- new_ext->handle = old_ext->handle;
+
+ for (i = 0; i < PAGE_OWNER_HANDLE_MAX; i++)
+ new_ext->handles[i] = old_ext->handles[i];

/*
* We don't clear the bit on the oldpage as it's going to be freed
@@ -292,7 +304,7 @@ void __dump_page_owner(struct page *page)
};
depot_stack_handle_t handle;
gfp_t gfp_mask;
- int mt;
+ int mt, i;

if (unlikely(!page_ext)) {
pr_alert("There is not page extension available.\n");
@@ -301,25 +313,31 @@ void __dump_page_owner(struct page *page)
gfp_mask = page_ext->gfp_mask;
mt = gfpflags_to_migratetype(gfp_mask);

- if (!test_bit(PAGE_EXT_OWNER_ALLOC, &page_ext->flags)) {
+ if (!test_bit(PAGE_EXT_OWNER_ALLOC, &page_ext->flags) &&
+ !test_bit(PAGE_EXT_OWNER_FREE, &page_ext->flags)) {
pr_alert("page_owner info is not active (free page?)\n");
return;
}

- handle = READ_ONCE(page_ext->handle);
- if (!handle) {
- pr_alert("page_owner info is not active (free page?)\n");
- return;
- }
+ for (i = 0; i < PAGE_OWNER_HANDLE_MAX; i++) {
+ handle = READ_ONCE(page_ext->handles[i]);
+ if (!handle) {
+ pr_alert("page_owner info is not active for `%s'\n",
+ page_owner_handles_names[i]);
+ continue;
+ }

- depot_fetch_stack(handle, &trace);
- pr_alert("page allocated via order %u, migratetype %s, gfp_mask %#x(%pGg)\n",
- page_ext->order, migratetype_names[mt], gfp_mask, &gfp_mask);
- print_stack_trace(&trace, 0);
+ depot_fetch_stack(handle, &trace);
+ pr_alert("%s via order %u, migratetype %s, gfp_mask %#x(%pGg)\n",
+ page_owner_handles_names[i], page_ext->order,
+ migratetype_names[mt], gfp_mask, &gfp_mask);
+ print_stack_trace(&trace, 0);

- if (page_ext->last_migrate_reason != -1)
+ if (page_ext->last_migrate_reason == -1)
+ continue;
pr_alert("page has been migrated, last migrate reason: %s\n",
migrate_reason_names[page_ext->last_migrate_reason]);
+ }
}

static ssize_t
@@ -381,7 +399,7 @@ read_page_owner(struct file *file, char __user *buf, size_t count, loff_t *ppos)
* Access to page_ext->handle isn't synchronous so we should
* be careful to access it.
*/
- handle = READ_ONCE(page_ext->handle);
+ handle = READ_ONCE(page_ext->handles[PAGE_OWNER_HANDLE_ALLOC]);
if (!handle)
continue;

--
2.9.0.243.g5c589a7