[PATCH v2] mm/page_isolation: don't putback unisolated page

[PATCH v2] mm/page_isolation: don't putback unisolated page

[Miaohe Lin]

If __isolate_free_page() failed, due to zone watermark check, the page is
still on the free list. But this page will be put back to free list again
via __putback_isolated_page() now. This may trigger page->flags checks in
__free_one_page() if PageReported is set. Or we will corrupt the free list
because list_add() will be called for pages already on another list.

Fixes: 3c605096d315 ("mm/page_alloc: restrict max order of merging on isolated pageblock")
Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
---
v1->v2:
  Add VM_WARN_ON to catch unexpected isolating failure.
---
 mm/page_isolation.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index f93cc63d8fa1..f67c4c70f17f 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -94,8 +94,13 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
 			buddy = page + (buddy_pfn - pfn);
 
 			if (!is_migrate_isolate_page(buddy)) {
-				__isolate_free_page(page, order);
-				isolated_page = true;
+				isolated_page = !!__isolate_free_page(page, order);
+				/*
+				 * Isolating a free page in an isolated pageblock
+				 * is expected to always work as watermarks don't
+				 * apply here.
+				 */
+				VM_WARN_ON(!isolated_page);
 			}
 		}
 	}
-- 
2.23.0

Re: [PATCH v2] mm/page_isolation: don't putback unisolated page

[David Hildenbrand]

On 13.09.21 13:50, Miaohe Lin wrote:
> If __isolate_free_page() failed, due to zone watermark check, the page is
> still on the free list. But this page will be put back to free list again
> via __putback_isolated_page() now. This may trigger page->flags checks in
> __free_one_page() if PageReported is set. Or we will corrupt the free list
> because list_add() will be called for pages already on another list.
> 
> Fixes: 3c605096d315 ("mm/page_alloc: restrict max order of merging on isolated pageblock")
> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
> ---
> v1->v2:
>    Add VM_WARN_ON to catch unexpected isolating failure.
> ---
>   mm/page_isolation.c | 9 +++++++--
>   1 file changed, 7 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
> index f93cc63d8fa1..f67c4c70f17f 100644
> --- a/mm/page_isolation.c
> +++ b/mm/page_isolation.c
> @@ -94,8 +94,13 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
>   			buddy = page + (buddy_pfn - pfn);
>   
>   			if (!is_migrate_isolate_page(buddy)) {
> -				__isolate_free_page(page, order);
> -				isolated_page = true;
> +				isolated_page = !!__isolate_free_page(page, order);
> +				/*
> +				 * Isolating a free page in an isolated pageblock
> +				 * is expected to always work as watermarks don't
> +				 * apply here.
> +				 */
> +				VM_WARN_ON(!isolated_page);


Didn't we discuss that this can never happen?

In that case, the patch description+subject needs updating and the 
"Fixes" line would be wrong.

>   			}
>   		}
>   	}
> 


-- 
Thanks,

David / dhildenb

Re: [PATCH v2] mm/page_isolation: don't putback unisolated page

[Miaohe Lin]

On 2021/9/13 20:15, David Hildenbrand wrote:
> On 13.09.21 13:50, Miaohe Lin wrote:
>> If __isolate_free_page() failed, due to zone watermark check, the page is
>> still on the free list. But this page will be put back to free list again
>> via __putback_isolated_page() now. This may trigger page->flags checks in
>> __free_one_page() if PageReported is set. Or we will corrupt the free list
>> because list_add() will be called for pages already on another list.
>>
>> Fixes: 3c605096d315 ("mm/page_alloc: restrict max order of merging on isolated pageblock")
>> Signed-off-by: Miaohe Lin <linmiaohe@huawei.com>
>> ---
>> v1->v2:
>>    Add VM_WARN_ON to catch unexpected isolating failure.
>> ---
>>   mm/page_isolation.c | 9 +++++++--
>>   1 file changed, 7 insertions(+), 2 deletions(-)
>>
>> diff --git a/mm/page_isolation.c b/mm/page_isolation.c
>> index f93cc63d8fa1..f67c4c70f17f 100644
>> --- a/mm/page_isolation.c
>> +++ b/mm/page_isolation.c
>> @@ -94,8 +94,13 @@ static void unset_migratetype_isolate(struct page *page, unsigned migratetype)
>>               buddy = page + (buddy_pfn - pfn);
>>                 if (!is_migrate_isolate_page(buddy)) {
>> -                __isolate_free_page(page, order);
>> -                isolated_page = true;
>> +                isolated_page = !!__isolate_free_page(page, order);
>> +                /*
>> +                 * Isolating a free page in an isolated pageblock
>> +                 * is expected to always work as watermarks don't
>> +                 * apply here.
>> +                 */
>> +                VM_WARN_ON(!isolated_page);
> 
> 
> Didn't we discuss that this can never happen?
> 
> In that case, the patch description+subject needs updating and the "Fixes" line would be wrong.
> 

I thought this might need a Fixes tag... Will change all of these. Many thanks.

>>               }
>>           }
>>       }
>>
> 
>