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SubjectRe: [PATCH 3/3] mm/page_owner: track page free call chain
On Sun, Jul 03, 2016 at 01:16:56AM +0900, Sergey Senozhatsky wrote:
> Introduce PAGE_OWNER_TRACK_FREE config option to 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.

Hmm... Do you have other ideas to use this feature? Following example is
just to detect use-after-free and we have other good tools for it
(KASAN or DEBUG_PAGEALLOC) so I'm not sure whether it's useful or not.

And, if there is a good usage, I think that we don't need to add new
Kconfig, PAGE_OWNER_TRACK_FREE. It only takes 8 bytes per page and
it's not that big in this debugging context.

Thanks.

>
> Aa a trivial example, let's assume that do_some_foo() has an error - 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);
> }
>
>
> 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 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 | 13 ++++++-
> lib/Kconfig.debug | 10 +++++
> mm/page_owner.c | 98 ++++++++++++++++++++++++++++++++++--------------
> mm/vmstat.c | 3 ++
> 4 files changed, 95 insertions(+), 29 deletions(-)
>
> diff --git a/include/linux/page_ext.h b/include/linux/page_ext.h
> index 66ba2bb..90bd44a 100644
> --- a/include/linux/page_ext.h
> +++ b/include/linux/page_ext.h
> @@ -27,12 +27,23 @@ 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,
> +#ifdef CONFIG_PAGE_OWNER_TRACK_FREE
> + PAGE_OWNER_HANDLE_FREE,
> +#endif
> + 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 +57,7 @@ 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/lib/Kconfig.debug b/lib/Kconfig.debug
> index 0f99819..20ac03b 100644
> --- a/lib/Kconfig.debug
> +++ b/lib/Kconfig.debug
> @@ -260,6 +260,16 @@ config PAGE_OWNER
>
> If unsure, say N.
>
> +config PAGE_OWNER_TRACK_FREE
> + bool "Track page free call chains"
> + depends on PAGE_OWNER
> + help
> + Page owner keeps track of what call chain is the owner of a page (has
> + allocated the page), this option enables an additional functionality
> + to also track what call chain has freed the page.
> +
> + If unsure, say N.
> +
> config DEBUG_FS
> bool "Debug Filesystem"
> select SRCU
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index 4acccb7..5a108d6 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -13,6 +13,13 @@
>
> #define PAGE_OWNER_STACK_DEPTH (16)
>
> +static const char *page_owner_handles_names[PAGE_OWNER_HANDLE_MAX] = {
> + "page allocated",
> +#ifdef CONFIG_PAGE_OWNER_TRACK_FREE
> + "page freed",
> +#endif
> +};
> +
> static bool page_owner_disabled = true;
> DEFINE_STATIC_KEY_FALSE(page_owner_inited);
>
> @@ -85,19 +92,6 @@ 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 +141,45 @@ static noinline depot_stack_handle_t save_stack(gfp_t flags)
> return handle;
> }
>
> +#ifdef CONFIG_PAGE_OWNER_TRACK_FREE
> +void __page_owner_free_pages(struct page *page, unsigned int order)
> +{
> + int i;
> + depot_stack_handle_t handle;
> + struct page_ext *page_ext = lookup_page_ext(page);
> +
> + if (unlikely(!page_ext))
> + return;
> +
> + handle = save_stack(0);
> + page_ext->handles[PAGE_OWNER_HANDLE_FREE] = handle;
> + __set_bit(PAGE_EXT_OWNER_FREE, &page_ext->flags);
> +
> + for (i = 1; i < (1 << order); i++) {
> + struct page_ext *ext = lookup_page_ext(page + 1);
> +
> + if (unlikely(!ext))
> + continue;
> + ext->handles[PAGE_OWNER_HANDLE_FREE] = handle;
> + __set_bit(PAGE_EXT_OWNER_FREE, &ext->flags);
> + }
> +}
> +#else
> +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);
> + }
> +}
> +#endif
> +
> noinline void __page_owner_alloc_pages(struct page *page, unsigned int order,
> gfp_t gfp_mask)
> {
> @@ -155,7 +188,7 @@ 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 +222,7 @@ 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 +230,9 @@ 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 +328,7 @@ 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 +337,31 @@ 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 +423,7 @@ 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;
>
> diff --git a/mm/vmstat.c b/mm/vmstat.c
> index 63ef65f..4ff0135 100644
> --- a/mm/vmstat.c
> +++ b/mm/vmstat.c
> @@ -1073,6 +1073,9 @@ static void pagetypeinfo_showmixedcount_print(struct seq_file *m,
> if (!test_bit(PAGE_EXT_OWNER_ALLOC, &page_ext->flags))
> continue;
>
> + if (!test_bit(PAGE_EXT_OWNER_FREE, &page_ext->flags))
> + continue;
> +
> page_mt = gfpflags_to_migratetype(page_ext->gfp_mask);
> if (pageblock_mt != page_mt) {
> if (is_migrate_cma(pageblock_mt))
> --
> 2.9.0.37.g6d523a3
>
> --
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