2018-03-21 04:39:29

by Maninder Singh

Subject: [PATCH 1/1] mm/page_owner: fix recursion bug after changing skip entries

This patch fixes "5f48f0bd4e368425db4424b9afd1bd251d32367a".
(mm, page_owner: skip unnecessary stack_trace entries)

Because if we skip first two entries then logic of checking count
value as 2 for recursion is broken and code will go in one depth
recursion.

so we need to check only one call of _RET_IP(__set_page_owner)
while checking for recursion.

Current Backtrace while checking for recursion:-

(save_stack) from (__set_page_owner) // (But recursion returns true here)
(__set_page_owner) from (get_page_from_freelist)
(get_page_from_freelist) from (__alloc_pages_nodemask)
(__alloc_pages_nodemask) from (depot_save_stack)
(depot_save_stack) from (save_stack) // recursion should return true here
(save_stack) from (__set_page_owner)
(__set_page_owner) from (get_page_from_freelist)
(get_page_from_freelist) from (__alloc_pages_nodemask+)
(__alloc_pages_nodemask) from (depot_save_stack)
(depot_save_stack) from (save_stack)
(save_stack) from (__set_page_owner)
(__set_page_owner) from (get_page_from_freelist)

Correct Backtrace with fix:

(save_stack) from (__set_page_owner) // recursion returned true here
(__set_page_owner) from (get_page_from_freelist)
(get_page_from_freelist) from (__alloc_pages_nodemask+)
(__alloc_pages_nodemask) from (depot_save_stack)
(depot_save_stack) from (save_stack)
(save_stack) from (__set_page_owner)
(__set_page_owner) from (get_page_from_freelist)

Signed-off-by: Maninder Singh <[email protected]>
Signed-off-by: Vaneet Narang <[email protected]>
---
mm/page_owner.c | 6 +++---
1 files changed, 3 insertions(+), 3 deletions(-)

diff --git a/mm/page_owner.c b/mm/page_owner.c
index 8592543..46ab1c4 100644
--- a/mm/page_owner.c
+++ b/mm/page_owner.c
@@ -123,13 +123,13 @@ void __reset_page_owner(struct page *page, unsigned int order)
static inline bool check_recursive_alloc(struct stack_trace *trace,
unsigned long ip)
{
- int i, count;
+ int i;

if (!trace->nr_entries)
return false;

- for (i = 0, count = 0; i < trace->nr_entries; i++) {
- if (trace->entries[i] == ip && ++count == 2)
+ for (i = 0; i < trace->nr_entries; i++) {
+ if (trace->entries[i] == ip)
return true;
}

--
1.7.1

2018-03-21 08:28:52

by Vlastimil Babka

Subject: Re: [PATCH 1/1] mm/page_owner: fix recursion bug after changing skip entries

On 03/21/2018 05:37 AM, Maninder Singh wrote:
> This patch fixes "5f48f0bd4e368425db4424b9afd1bd251d32367a".
> (mm, page_owner: skip unnecessary stack_trace entries)
>
> Because if we skip first two entries then logic of checking count
> value as 2 for recursion is broken and code will go in one depth
> recursion.
>
> so we need to check only one call of _RET_IP(__set_page_owner)
> while checking for recursion.
>
> Current Backtrace while checking for recursion:-
>
> (save_stack) from (__set_page_owner) // (But recursion returns true here)
> (__set_page_owner) from (get_page_from_freelist)
> (get_page_from_freelist) from (__alloc_pages_nodemask)
> (__alloc_pages_nodemask) from (depot_save_stack)
> (depot_save_stack) from (save_stack) // recursion should return true here
> (save_stack) from (__set_page_owner)
> (__set_page_owner) from (get_page_from_freelist)
> (get_page_from_freelist) from (__alloc_pages_nodemask+)
> (__alloc_pages_nodemask) from (depot_save_stack)
> (depot_save_stack) from (save_stack)
> (save_stack) from (__set_page_owner)
> (__set_page_owner) from (get_page_from_freelist)
>
> Correct Backtrace with fix:
>
> (save_stack) from (__set_page_owner) // recursion returned true here
> (__set_page_owner) from (get_page_from_freelist)
> (get_page_from_freelist) from (__alloc_pages_nodemask+)
> (__alloc_pages_nodemask) from (depot_save_stack)
> (depot_save_stack) from (save_stack)
> (save_stack) from (__set_page_owner)
> (__set_page_owner) from (get_page_from_freelist)
>
> Signed-off-by: Maninder Singh <[email protected]>
> Signed-off-by: Vaneet Narang <[email protected]>
Fixes: 5f48f0bd4e36 ("mm, page_owner: skip unnecessary stack_trace entries")

Good catch.
Acked-by: Vlastimil Babka <[email protected]>

> ---
> mm/page_owner.c | 6 +++---
> 1 files changed, 3 insertions(+), 3 deletions(-)
>
> diff --git a/mm/page_owner.c b/mm/page_owner.c
> index 8592543..46ab1c4 100644
> --- a/mm/page_owner.c
> +++ b/mm/page_owner.c
> @@ -123,13 +123,13 @@ void __reset_page_owner(struct page *page, unsigned int order)
> static inline bool check_recursive_alloc(struct stack_trace *trace,
> unsigned long ip)
> {
> - int i, count;
> + int i;
>
> if (!trace->nr_entries)
> return false;
>
> - for (i = 0, count = 0; i < trace->nr_entries; i++) {
> - if (trace->entries[i] == ip && ++count == 2)
> + for (i = 0; i < trace->nr_entries; i++) {
> + if (trace->entries[i] == ip)
> return true;
> }
>
>