Re: [PATCH v3] mm/kasan: dump alloc and free stack for page allocator

Vlastimil Babka
2019-09-12T13:53:54Z

On 9/11/19 5:19 PM, Qian Cai wrote:
>
> The new config looks redundant and confusing. It looks to me more of a document update
> in Documentation/dev-tools/kasan.txt to educate developers to select PAGE_OWNER and
> DEBUG_PAGEALLOC if needed.

Agreed. But if you want it fully automatic, how about something
like this (on top of mmotm/next)? If you agree I'll add changelog
and send properly.

----8<----

From a528d14c71d7fdf5872ca8ab3bd1b5bad26670c9 Mon Sep 17 00:00:00 2001
From: Vlastimil Babka <vbabka@suse.cz>
Date: Thu, 12 Sep 2019 15:51:23 +0200
Subject: [PATCH] make KASAN enable page_owner with free stack capture

---
include/linux/page_owner.h | 1 +
lib/Kconfig.kasan | 4 ++++
mm/Kconfig.debug | 5 +++++
mm/page_alloc.c | 6 +++++-
mm/page_owner.c | 37 ++++++++++++++++++++++++-------------
5 files changed, 39 insertions(+), 14 deletions(-)

diff --git a/include/linux/page_owner.h b/include/linux/page_owner.h
index 8679ccd722e8..6ffe8b81ba85 100644
--- a/include/linux/page_owner.h
+++ b/include/linux/page_owner.h
@@ -6,6 +6,7 @@

#ifdef CONFIG_PAGE_OWNER
extern struct static_key_false page_owner_inited;
+extern bool page_owner_free_stack_disabled;
extern struct page_ext_operations page_owner_ops;

extern void __reset_page_owner(struct page *page, unsigned int order);
diff --git a/lib/Kconfig.kasan b/lib/Kconfig.kasan
index 6c9682ce0254..dc560c7562e8 100644
--- a/lib/Kconfig.kasan
+++ b/lib/Kconfig.kasan
@@ -41,6 +41,8 @@ config KASAN_GENERIC
select SLUB_DEBUG if SLUB
select CONSTRUCTORS
select STACKDEPOT
+ select PAGE_OWNER
+ select PAGE_OWNER_FREE_STACK
help
Enables generic KASAN mode.
Supported in both GCC and Clang. With GCC it requires version 4.9.2
@@ -63,6 +65,8 @@ config KASAN_SW_TAGS
select SLUB_DEBUG if SLUB
select CONSTRUCTORS
select STACKDEPOT
+ select PAGE_OWNER
+ select PAGE_OWNER_FREE_STACK
help
Enables software tag-based KASAN mode.
This mode requires Top Byte Ignore support by the CPU and therefore
diff --git a/mm/Kconfig.debug b/mm/Kconfig.debug
index 327b3ebf23bf..a71d52636687 100644
--- a/mm/Kconfig.debug
+++ b/mm/Kconfig.debug
@@ -13,6 +13,7 @@ config DEBUG_PAGEALLOC
depends on DEBUG_KERNEL
depends on !HIBERNATION || ARCH_SUPPORTS_DEBUG_PAGEALLOC && !PPC && !SPARC
select PAGE_POISONING if !ARCH_SUPPORTS_DEBUG_PAGEALLOC
+ select PAGE_OWNER_FREE_STACK if PAGE_OWNER
---help---
Unmap pages from the kernel linear mapping after free_pages().
Depending on runtime enablement, this results in a small or large
@@ -62,6 +63,10 @@ config PAGE_OWNER

If unsure, say N.

+config PAGE_OWNER_FREE_STACK
+ def_bool n
+ depends on PAGE_OWNER
+
config PAGE_POISONING
bool "Poison pages after freeing"
select PAGE_POISONING_NO_SANITY if HIBERNATION
diff --git a/mm/page_alloc.c b/mm/page_alloc.c
index c5d62f1c2851..d9e44671af3f 100644
--- a/mm/page_alloc.c
+++ b/mm/page_alloc.c
@@ -710,8 +710,12 @@ static int __init early_debug_pagealloc(char *buf)
if (kstrtobool(buf, &enable))
return -EINVAL;

- if (enable)
+ if (enable) {
static_branch_enable(&_debug_pagealloc_enabled);
+#ifdef CONFIG_PAGE_OWNER
+ page_owner_free_stack_disabled = false;
+#endif
+ }

return 0;
}
diff --git a/mm/page_owner.c b/mm/page_owner.c
index dee931184788..d4551d7012d0 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -24,13 +24,15 @@ struct page_owner {
short last_migrate_reason;
gfp_t gfp_mask;
depot_stack_handle_t handle;
-#ifdef CONFIG_DEBUG_PAGEALLOC
+#ifdef CONFIG_PAGE_OWNER_FREE_STACK
depot_stack_handle_t free_handle;
#endif
};

static bool page_owner_disabled = true;
+bool page_owner_free_stack_disabled = true;
DEFINE_STATIC_KEY_FALSE(page_owner_inited);
+static DEFINE_STATIC_KEY_FALSE(page_owner_free_stack);

static depot_stack_handle_t dummy_handle;
static depot_stack_handle_t failure_handle;
@@ -46,6 +48,11 @@ static int __init early_page_owner_param(char *buf)
if (strcmp(buf, "on") == 0)
page_owner_disabled = false;

+ if (IS_ENABLED(CONFIG_KASAN)) {
+ page_owner_disabled = false;
+ page_owner_free_stack_disabled = false;
+ }
+
return 0;
}
early_param("page_owner", early_page_owner_param);
@@ -91,6 +98,8 @@ static void init_page_owner(void)
register_failure_stack();
register_early_stack();
static_branch_enable(&page_owner_inited);
+ if (!page_owner_free_stack_disabled)
+ static_branch_enable(&page_owner_free_stack);
init_early_allocated_pages();
}

@@ -148,11 +157,11 @@ void __reset_page_owner(struct page *page, unsigned int order)
{
int i;
struct page_ext *page_ext;
-#ifdef CONFIG_DEBUG_PAGEALLOC
+#ifdef CONFIG_PAGE_OWNER_FREE_STACK
depot_stack_handle_t handle = 0;
struct page_owner *page_owner;

- if (debug_pagealloc_enabled())
+ if (static_branch_unlikely(&page_owner_free_stack))
handle = save_stack(GFP_NOWAIT | __GFP_NOWARN);
#endif

@@ -161,8 +170,8 @@ void __reset_page_owner(struct page *page, unsigned int order)
if (unlikely(!page_ext))
continue;
__clear_bit(PAGE_EXT_OWNER_ACTIVE, &page_ext->flags);
-#ifdef CONFIG_DEBUG_PAGEALLOC
- if (debug_pagealloc_enabled()) {
+#ifdef CONFIG_PAGE_OWNER_FREE_STACK
+ if (static_branch_unlikely(&page_owner_free_stack)) {
page_owner = get_page_owner(page_ext);
page_owner->free_handle = handle;
}
@@ -451,14 +460,16 @@ void __dump_page_owner(struct page *page)
stack_trace_print(entries, nr_entries, 0);
}

-#ifdef CONFIG_DEBUG_PAGEALLOC
- handle = READ_ONCE(page_owner->free_handle);
- if (!handle) {
- pr_alert("page_owner free stack trace missing\n");
- } else {
- nr_entries = stack_depot_fetch(handle, &entries);
- pr_alert("page last free stack trace:\n");
- stack_trace_print(entries, nr_entries, 0);
+#ifdef CONFIG_PAGE_OWNER_FREE_STACK
+ if (static_branch_unlikely(&page_owner_free_stack)) {
+ handle = READ_ONCE(page_owner->free_handle);
+ if (!handle) {
+ pr_alert("page_owner free stack trace missing\n");
+ } else {
+ nr_entries = stack_depot_fetch(handle, &entries);
+ pr_alert("page last free stack trace:\n");
+ stack_trace_print(entries, nr_entries, 0);
+ }
}
#endif

--
2.23.0