Re: [PATCH] 4.1.28 Fix bad backport of 8f182270dfec "mm/swap.c: flush lru pvecs on compound page arrival"

[Michal Hocko <mhocko@kernel.org>]

On Thu 14-07-16 17:55:21, Steven Rostedt wrote:
> When I pulled in 4.1.28 into my stable 4.1-rt tree and ran the tests,
> it crashed with a severe OOM killing everything. I then tested 4.1.28
> without -rt and it had the same issue. I did a bisect between 4.1.27
> and 4.1.28 and found that the bug started at:
> 
> commit 8f182270dfec "mm/swap.c: flush lru pvecs on compound page
> arrival"
> 
> Looking at that patch and what's in mainline, I see that there's a
> mismatch in one of the hunks:
> 
> Mainline:
> 
> @@ -391,9 +391,8 @@ static void __lru_cache_add(struct page *page)
>         struct pagevec *pvec = &get_cpu_var(lru_add_pvec);
> 
>         get_page(page);
> -       if (!pagevec_space(pvec))
> +       if (!pagevec_add(pvec, page) || PageCompound(page))
>                 __pagevec_lru_add(pvec);
> -       pagevec_add(pvec, page);
>         put_cpu_var(lru_add_pvec);
>  }
> 
> 
> Stable 4.1.28:
> 
> @@ -631,9 +631,8 @@ static void __lru_cache_add(struct page *page)
>         struct pagevec *pvec = &get_cpu_var(lru_add_pvec);
> 
>         page_cache_get(page);
> -       if (!pagevec_space(pvec))
> +       if (!pagevec_space(pvec) || PageCompound(page))
>                 __pagevec_lru_add(pvec);
> -       pagevec_add(pvec, page);
>         put_cpu_var(lru_add_pvec);
>  }

Heh, I've made the same mistake when backporting this to our older SLES
based kernel initially. I was lucky the system even didn't boot. Sorry
that I didn't find time to review the stable backport.

> Where mainline replace pagevec_space() with pagevec_add, and stable did
> not.
> 
> Fixing this makes the OOM go away.
> 
> Note, 3.18 has the same bug.
> 
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>

Acked-by: Michal Hocko <mhocko@suse.com>

> ---
> diff --git a/mm/swap.c b/mm/swap.c
> index b523f0a4cbfb..ab3b9c2dd783 100644
> --- a/mm/swap.c
> +++ b/mm/swap.c
> @@ -631,7 +631,7 @@ static void __lru_cache_add(struct page *page)
>  	struct pagevec *pvec = &get_cpu_var(lru_add_pvec);
>  
>  	page_cache_get(page);
> -	if (!pagevec_space(pvec) || PageCompound(page))
> +	if (!pagevec_add(pvec, page) || PageCompound(page))
>  		__pagevec_lru_add(pvec);
>  	put_cpu_var(lru_add_pvec);
>  }

-- 
Michal Hocko
SUSE Labs